Module 3
Microbial Nutrition, Growth, and Metabolism
Microbial Nutrition and Growth
With respect to nutrition, microbes are not really so different from humans. All
organisms require a constant influx of certain substances from their habitat. Even bacteria living
in mud on a diet of inorganic sulfur, or protozoa digesting wood in a termite’s intestine, have
some basic nutritional needs. In general, all living things require a source of elements such as
carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, iron, sodium,
chlorine, and magnesium. But the ultimate source of a particular element, its chemical form, and
how much of it the microbe needs are all points of variation between different types of
organisms.
Any substance that must be provided to an organism is called an essential nutrient. Two
categories of essential nutrients are macronutrients and micronutrients. Macronutrients are
required in relatively large quantities and play principal roles in cell structure and metabolism.
Examples of macronutrients are carbon, hydrogen, and oxygen. Micronutrients, or trace
elements, such as manganese, zinc, and nickel, are present in much smaller amounts and are
involved in enzyme function and maintenance of protein structure. Another way to categorize
nutrients is according to their carbon content.
An inorganic nutrient is an atom or simple molecule that contains a combination of atoms
other than carbon and hydrogen. The natural reservoirs of inorganic compounds are mineral
deposits in the crust of the earth, bodies of water, and the atmosphere. Examples include metals
and their salts (magnesium sulfate, ferric nitrate, sodium phosphate), gases (oxygen, carbon
dioxide), and water. In contrast, the molecules of organic nutrients contain carbon and hydrogen
atoms and are usually the products of living things. They range from the simplest organic
molecule, methane (CH4), to large polymers (carbohydrates, lipids, proteins, and nucleic acids).
The source of nutrients is extremely varied: Some microbes obtain their nutrients entirely from
inorganic sources, and others require a combination of organic and inorganic sources.
The earth’s limitless habitats and microbial adaptations make for an elaborate menu of
microbial nutritional schemes. Fortunately, most organisms show consistent trends and can be
described by a few general categories (table 6.2) and a few selected terms. To keep these straight
you should always remember that the main determinants of a microbe’s nutritional type are its
source of carbon and its source of energy. We’ll start with an organism’s carbon source: In this
regard, microbes are either heterotrophs or autotrophs. A heterotroph is an organism that must
obtain its carbon in an organic form. An autotroph (“self-feeder”) is an organism that uses
inorganic CO2 as its carbon source. Because autotrophs have the special capacity to convert CO2
into organic compounds, they are not nutritionally dependent on other living things.
Autotrophs—that is, organisms that get their carbon from CO2—derive energy from one
of two possible nonliving sources: sunlight and chemical reactions involving simple chemicals.
When they get their energy from sunlight, they are called photoautotrophs, and when they get it
from chemicals, they are called chemoautotrophs. Photoautotrophs are photosynthetic—that is,
they capture the energy of light rays and transform it into chemical energy that can be used in
cell metabolism. Because photosynthetic organisms (algae, plants, some bacteria) produce
organic molecules that can be used by themselves and by heterotrophs, they form the basis for
most food webs. Chemoautotrophs are of two types: One of these is the group called
chemoorganic autotrophs. These use organic compounds for energy and inorganic compounds as
a carbon source. The second type of chemoautotroph is a group called lithoautotrophs, which
require neither sunlight nor organic nutrients, relying totally on inorganic minerals. These
bacteria derive energy in diverse and rather amazing ways. In very simple terms, they remove
electrons from inorganic substrates—such as hydrogen gas, hydrogen sulfide, sulfur, or iron—
and combine them with carbon dioxide and hydrogen.
Saprobes occupy a niche as decomposers of plant litter, animal matter, and dead
microbes. If not for the work of these decomposers, the earth would gradually fill up with
organic material, and the nutrients it contains would not be recycled. Parasites live in or on the
body of a host, which they harm to some degree. Because many parasites cause damage to
tissues (disease) or even death, they are also called pathogens. Parasites range from viruses to
helminths (worms), and they can live on the body (ectoparasites), in the organs and tissues
(endoparasites), or even within cells (intracellular parasites, the most extreme type). Obligate
parasites (for example, the leprosy bacillus and the syphilis spirochete) are unable to grow
outside of a living host. Parasites that have less strict requirements can be cultured artificially if
provided with the correct nutrients and environmental conditions. Bacteria such as Streptococcus
pyogenes (the cause of strep throat) and Staphylococcus aureus can grow on artificial media.
Mineral ions are also important components in microbial metabolism. Potassium is
essential to protein synthesis and membrane function. Sodium is important for certain types of
cell transport. Calcium is a stabilizer of the cell wall and endospores of bacteria. Magnesium is a
component of chlorophyll and a stabilizer of membranes and ribosomes. Iron is an important
component of the cytochrome proteins of cell respiration. Zinc is an essential regulatory element
for eukaryotic genetics. It is a major component of “zinc fingers”—binding factors that help
enzymes adhere to specific sites on DNA. Copper, cobalt, nickel, molybdenum, manganese,
silicon, iodine, and boron are needed in small amounts by some microbes but not others. On the
other hand, in chapter 9 you will see that metals can also be very toxic to microbes. The
concentration of metal ions can even influence the diseases microbes cause. For example, the
bacteria that cause gonorrhea and meningitis grow more rapidly in the presence of iron.
A slightly hypotonic environment can be a good situation for bacterial cells. The constant
slight tendency for water to flow into the cell keeps the cytoplasmic membrane fully extended
and the cytoplasm full. This is the optimum condition for the many processes occurring in and on
the membrane. Slight hypotonicity is tolerated quite well by most bacteria because of their rigid
cell walls. Hypertonic conditions are also out of balance with the tonicity of the cell’s cytoplasm,
but in this case, the environment has a higher solute concentration than the cytoplasm. Because a
hypertonic environment will force water to diffuse out of a cell, it is said to have high osmotic
pressure, or potential. Microbes in hypertonic solutions often cannot grow or metabolize because
their membranes are so wrinkled up that many cell processes are impossible. This is the principle
behind using concentrated salt and sugar solutions as preservatives for food, such as in salted
hams, because the microbes in them will be stopped from growing by the hypertonic state.
Environmental Factors That Influence Microbes
Microbes are exposed to a wide variety of environmental factors in addition to nutrients.
These include such factors as heat, cold, gases, pH, radiation, osmotic and hydrostatic pressures,
and even the effects of other microbes. For most microbes, environmental factors fundamentally
affect the function of metabolic enzymes. Survival in a changing environment is largely a matter
of whether the enzyme systems of microorganisms can adapt to alterations in their habitat.
Microbial cells are unable to control their own temperature and therefore take on the
ambient temperature of their natural habitats. Their survival is dependent on adapting to
whatever temperature variations are encountered in that habitat. The range of temperatures for
the growth of a given microbial species can be expressed as three cardinal temperatures. The
minimum temperature is the lowest temperature that permits a microbe’s continued growth and
metabolism. Below this temperature, its activities stop. The maximum temperature is the highest
temperature at which growth and metabolism can proceed. If the temperature rises slightly above
maximum, growth will temporarily stop, but if it continues to rise beyond that point, the enzymes
and nucleic acids will eventually become permanently inactivated (otherwise known as
denaturation), and the cell will die. This is why heat works so well as an agent in microbial
control.
The optimum temperature covers a small range, intermediate between the minimum and
maximum, which promotes the fastest rate of growth and metabolism (rarely is the optimum a
single point). Depending on their natural habitats, some microbes have a narrow cardinal range,
others a broad one. Some strict parasites will not grow if the temperature varies more than a few
degrees below or above the host’s body temperature. For instance, the typhus bacterium
multiplies only in the range of 32°C to 38°C, and rhinoviruses (one cause of the common cold)
multiply most successfully in tissues that are slightly below normal body temperature (33°C to
35°C). Other organisms are not so limited. Strains of Staphylococcus aureus grow within the
range of 6°C to 46°C, and the intestinal bacterium Enterococcus faecalis grows within the range
of 0°C to 44°C. Another way to express temperature adaptation is to describe whether an
organism grows optimally in a cold, moderate, or hot temperature range. The terms used for
these ecological groups are psychrophile, mesophile, and thermophile (figure 6.4), respectively
A psychrophile (sy´-kroh-fyl)—the blue line in figure 6.4—is a microorganism that has
an optimum temperature below 15°C and is still capable of growth at 0°C. It is obligate with
respect to cold (i.e., it can only grow in cold temperatures) and generally cannot grow above
20°C. Unlike most laboratory cultures, storage in the refrigerator causes them to grow, rather
than inhibiting them. As one might predict, the habitats of psychrophilic bacteria, fungi, and
algae are lakes and rivers, snowfields (figure 6.5), polar ice, and the deep ocean. Rarely, if ever,
are they pathogenic. True psychrophiles must be distinguished from the less extreme
psychrotolerant (the gold line in figure 6.4) that grow slowly in cold but have an optimum
temperature between 15°C and 30°C.
The majority of medically significant microorganisms are mesophiles (mez´-oh-fylz; the
green line in figure 6.4), organisms that grow at intermediate temperatures. The optimum growth
temperatures (optima) of most mesophiles fall into the range of 20°C to 40°C. Organisms in this
group inhabit animals and plants as well as soil and water in temperate, subtropical, and tropical
regions. Most human pathogens grow optimally somewhere between 30°C and 40°C (human
body temperature is 37°C). Some mesophilic bacteria, such as Staphylococcus aureus, grow
optimally at body temperature but are also facultatively psychrotolerant meaning they can
survive and multiply slowly at refrigerator temperatures, causing concern for food storage.
(Facultative is a term used in biology that designates an organism as capable of growing under
differing sets of conditions. We will see the term again when we discuss oxygen requirements.)
Listeria monocytogenes is a human pathogen that is truly psychrotolerant, meaning its optimum
growth is between 30°C and 40°C. But it will grow slowly at temperatures as low as 1°C, and
often grows in ice cream and refrigerated meat.
Thermoduric microbes, which can survive short exposure to high temperatures but are
normally mesophiles, are common contaminants of heated or pasteurized foods. Examples
include heat-resistant endospore formers such as Bacillus and Clostridium. A thermophile (thur´-
moh-fyl; the pink line in figure 6.4) is a microbe that grows optimally at temperatures greater
than 45°C. Such heat-loving microbes live in soil and water associated with volcanic activity, in
compost piles, and in habitats directly exposed to the sun. Thermophiles vary in heat
requirements, with a general range of growth of 45°C to 80°C. Most eukaryotic forms cannot
survive above 60°C, but a few thermophilic bacteria, called extreme thermophiles (the brown
line in figure 6.4), grow between 80°C and 121°C.
Although all microbes require some carbon dioxide in their metabolism, capnophiles
grow best at a higher CO2 tension than is normally present in the atmosphere. Some notable
capnophiles are Neisseria (a genus causing gonorrhea and meningitis), Brucella (undulant fever),
and Streptococcus pneumoniae. Growing these from clinical specimens requires providing a
higher CO2 tension than normal. The term pH is defined as the degree of acidity or alkalinity
(basicity) of a solution. It is expressed by the pH scale, a series of numbers ranging from 0 to 14.
The pH of fresh pure water (7.0) is neutral, neither acidic nor basic. As the pH value decreases
toward 0, the acidity increases, and as the pH increases toward 14, the alkalinity increases. The
majority of organisms are neutrophiles and live or grow in habitats between pH 6 and 8 because
strong acids and bases can be highly damaging to enzymes and other cellular substances.
Although most microbes exist under hypotonic or isotonic conditions, a few, called
osmophiles, live in habitats with a high solute concentration. One common type of osmophile
prefers high concentrations of salt; these organisms are called halophiles (hay´-loh-fylz).
Obligate halophiles such as Halobacterium and Halococcus inhabit salt lakes, ponds, and other
hypersaline habitats. They grow optimally in solutions of 25% NaCl but require at least 9% NaCl
(combined with other salts) for growth. These archaea have significant modifications in their cell
walls and membranes and will lyse in hypotonic habitats. Facultative halophiles are remarkably
resistant to salt, even though they do not normally reside in high-salt environments. For example,
Staphylococcus aureus can grow on NaCl media ranging from 0.1% up to 20%.
Up to now, we have considered the importance of nonliving environmental influences on
the growth of microorganisms. Another profound influence comes from other organisms that
share (or sometimes are) their habitats. In all but the rarest instances, microbes live in shared
habitats, which give rise to complex and fascinating associations. Some associations are between
similar or dissimilar types of microbes; others involve multicellular organisms such as animals or
plants. Interactions can have beneficial, harmful, or no particular effects on the organisms
involved. They can be obligatory or nonobligatory to the members; and they often involve
nutritional interactions.
Even when organisms are not engaged in symbiotic relationships, they are interacting.
Relationships between free-living species can have either negative or positive results.
Antagonism is an association between free-living species that arises when members of a
community compete. In this interaction, one microbe secretes chemical substances into the
surrounding environment that inhibit or destroy another microbe in the same habitat. The first
microbe may gain a competitive advantage by increasing the space and nutrients available to it.
Interactions of this type are common in the soil, where mixed communities often compete for
space and food. Antibiosis—the production of inhibitory compounds such as antibiotics—is
actually a form of antagonism.
Hundreds of naturally occurring antibiotics have been isolated from bacteria and fungi
and used as drugs to control diseases. Page 169 Synergism is an interrelationship between two or
more free-living organisms that benefits them but is not necessary for their survival. Together,
the participants cooperate to produce a result that none of them could do alone. Gum disease,
dental caries, and some bloodstream infections involve mixed infections by bacteria interacting
synergistically. Biofilms: The Epitome of Synergy Biofilms are communities of bacteria and/or
other microbes that are attached to a surface and to each other, forming a multilayer
conglomerate of cells and intracellular material. Usually there is a “pioneer” colonizer, a
bacterium that initially attaches to a surface, such as a tooth or the lung tissue (figure 6.7). Other
microbes then attach either to those bacteria or to the complex sugar and protein substance that
inevitably is secreted by microbial colonizers of surfaces. In many cases, once the cells are
attached, they are stimulated to release chemicals that accumulate as the cell population grows.
By this means, they can monitor the size of their own population.
This is a process called quorum sensing. Bacteria can use quorum sensing to interact with
other members of the same species, as well as members of other species that are close by.
Eventually large complex communities are formed, which have different physical and biological
characteristics in different locations of the community. The bottom of a biofilm may have very
different pH and oxygen conditions than the surface of a biofilm, for example. It is now clearly
established that microbes in a biofilm, as opposed to those in a planktonic (free-floating) state,
behave and respond very differently to their environments. Different genes are even activated in
the two situations. At any rate, a single biofilm is usually a partnership among multiple microbial
inhabitants and for that reason cannot be eradicated by traditional methods targeting individual
infections. This kind of synergism has led to the necessity of rethinking treatment of a great
many different conditions.
The Study of Bacterial Growth
Microorganisms can “grow” in many different ways. In chapter 5 you learned how
eukaryotic microbes grow. Here we focus on bacterial growth. While bacteria can be found that
grow through budding and hyphal formation (similar to fungi), the majority of bacteria grow by a
process called binary fission. Binary fission refers to the fact that one cell becomes two. During
binary fission, the parent cell enlarges, duplicates its chromosome, and then starts to pull its cell
envelope together in the center of the cell using a band of protein that is made of substances that
resemble actin and tubulin—the protein component of microtubules in eukaryotic cells. The cell
wall eventually forms a complete septum between the two about-to-be cells. This process divides
the cell into two daughter cells, and is then repeated at intervals by each new daughter cell in
turn. With each successive round of division, the population increases.
The time required for a complete fission cycle—from one parent cell to two new daughter
cells—is called the generation, or doubling, time. The term generation has a similar meaning as it
does in humans. It is the period between an individual’s birth and the time it produces offspring.
In bacteria, each new fission cycle, or generation, increases the population by a factor of 2, or
doubles it. The initial parent stage consists of 1 cell, the first generation consists of 2 cells, the
second 4, the third 8, then 16, 32, 64, and so on. As long as the environment remains favorable,
this doubling effect can continue at a constant rate. With the passing of each generation, the
population will double, over and over again.
The length of the generation time is a measure of the growth rate of an organism.
Compared with the growth rates of most other living things, bacteria are notoriously rapid. The
average generation time is 30 to 60 minutes under optimum conditions. The shortest generation
times can be 10 to 12 minutes, although some bacteria have generation times of days. For
example, Mycobacterium leprae, the cause of Hansen’s disease, has a generation time of 10 to 30
days—as long as that of some animals. Environmental bacteria commonly have generation times
measured in months. Most pathogens have relatively short doubling times. Salmonella enteritidis
and Staphylococcus aureus, bacteria that cause foodborne illness, double in 20 to 30 minutes,
which is why leaving food at room temperature even for a short period has caused many cases of
foodborne disease. In a few hours, a population of these bacteria can easily grow from a small
number of cells to several million. Figure 6.9 shows several quantitative characteristics of
growth: The cell population size can be represented by the number 2 with an exponent (2 1, 2 2,
2 3, 2 4); the exponent increases by one in each generation; and the number of the exponent is
also the number of the generation. This growth pattern is termed exponential. Because these
populations often contain very large numbers of cells, it is useful to express them by means of
exponents or logarithms. The data from a growing bacterial population are graphed by plotting
the number of cells as a function of time. Plotting the logarithm number (or exponent) over time
provides a straight line indicative of exponential growth. Plotting the data arithmetically gives a
constantly curved slope. In general, logarithmic graphs are preferred because an accurate cell
number is easier to read, especially during early growth phases.
Evaluating these agar plates involves a common and important principle in microbiology:
One colony on the plate represents one cell or colony-forming unit (CFU) from the original
sample. (The term “colony-forming unit” is used sometimes, acknowledging the fact that a group
of cells—such as a chain or a pair of connected bacteria—may be the one “unit” placed by itself
on that area of the agar.) Multiplication of the number of colonies in a single sample by the
container’s volume gives a fair estimate of the total population size (number of cells) at any
given point. In other words, you multiply the number of colonies arising from the fluid you
removed, by the dilution factor. For example, if you want to express the results as “per milliliter”
but you sampled only 1/10 of a milliliter, you just multiply the number of visible CFUs × 10.
The growth curve is determined by graphing the number for each sample in sequence for the
whole incubation period. Because there are few cells in the early stages of growth, very early
samples can give a zero reading even if there are viable cells in the culture. Also, the sampling
itself can remove enough viable cells to alter the tabulations, but because the purpose is to
compare relative trends in growth, these factors do not significantly change the overall pattern.
At the stationary growth phase, the population enters a period during which the rates of
cell birth and cell death are more or less equal. At this time, the division rate is slowing down
(making it easier for cell death to catch up with the rate of new cell formation). The decline in
the growth rate is caused by depleted nutrients and oxygen plus excretion of organic acids and
other biochemical pollutants into the growth medium, due to the increased density of cells. As
the limiting factors intensify, cells begin to die at an exponential rate (literally perishing in their
own wastes), and they are unable to multiply. The curve now dips downward as the death phase
begins. The speed with which death occurs depends on the relative resistance of the species and
how toxic the conditions are, but it is usually slower than the exponential growth phase. It is now
clear that many cells in a culture stay alive, but more or less dormant, for long periods of time.
They are so dormant that, although they are alive, they won’t grow on culture medium and
therefore are missed in colony counts. The name for this state is the viable nonculturable (VNC)
state.
Counting can be automated by sensitive devices such as the Coulter counter, which
electronically scans a fluid as it passes through a tiny pipette. As each cell flows by, it is detected
and registered on an electronic sensor (figure 6.14). A flow cytometer works on a similar
principle, but in addition to counting, it can measure cell size and even differentiate between live
and dead cells. When used in conjunction with fluorescent dyes and antibodies to tag cells, it has
been used to differentiate between gram-positive and gram-negative bacteria. It has been adapted
for use as a rapid method to identify pathogens in patient specimens and to differentiate blood
cells. More sophisticated forms of the flow cytometer can also sort cells of different types into
separate compartments of a collecting device. Although flow cytometry can be used to count
bacteria in natural samples without the need for culturing them, it requires fluorescent labeling of
the cells you are interested in detecting, which is not always possible.
Microbial Metabolism
Metabolism, from the Greek term metaballein, meaning “change,” pertains to all
chemical reactions and physical workings of the cell. Although metabolism entails thousands of
different reactions, most of them fall into one of two general categories. Anabolism, sometimes
also called biosynthesis, is any process that results in synthesis of cell molecules and structures.
It is a building and bond-making process that forms larger macromolecules from smaller ones,
and it usually requires the input of energy. Catabolism is the opposite of anabolism. Catabolic
reactions break the bonds of larger molecules into smaller molecules and often release energy. In
a cell, linking anabolism to catabolism ensures the efficient completion of many thousands of
processes. Another fundamental fact about metabolism is that electrons are critical to the
process.
An enzyme speeds up the rate of a metabolic reaction, but just how does it do this?
During a chemical reaction, reactants are converted to products either by bond formation or by
bond breakage. A certain amount of energy is required to initiate every such reaction, which
limits the rate at which reactions can happen. While the rate could be sped up by increased heat
or other means, biological cells use enzymes to vastly increase the speed of important reactions.
The molecules that are acted upon by enzymes are called substrates. At the molecular level, an
enzyme promotes a reaction by serving as a physical site upon which the substrates can be
positioned. The enzyme is almost always much larger in size than its substrate, and it presents a
unique active site that matches only that particular substrate. Although an enzyme binds to the
substrate and participates directly in changes to the substrate, it does not become a part of the
products, is not used up by the reaction, and can function over and over again. Enzyme speeds
are very rapid. Speeds range from a thousand substrate molecules converted per second for
lactate dehydrogenase to several million converted per second by the enzyme catalase.
In chapter 6, you learned that microorganisms require specific metal ions called trace
elements and also certain organic growth factors. In many cases, the need for these substances
arises from their roles as cofactors for enzymes. The metallic cofactors, including iron, copper,
magnesium, manganese, zinc, cobalt, selenium, and many others, have precise functions between
the enzyme and its substrate. In general, metals activate enzymes, help bring the active site and
substrate close together, and participate directly in chemical reactions with the enzyme-substrate
complex. Coenzymes are a type of cofactor. They are organic compounds that work in
conjunction with an apoenzyme to perform the alteration of a substrate. The general function of a
coenzyme is to remove a chemical group from one substrate molecule and add it to another
substrate, thereby serving as a transient carrier of this group. In a later section of this chapter, we
shall see that coenzymes carry and transfer hydrogen atoms, electrons, carbon dioxide, and
amino groups. Many coenzymes are derived from vitamins, which explains why vitamins are
important to nutrition and may be required as growth factors for living things. Vitamin
deficiencies can prevent the complete holoenzyme from forming. Consequently, both the
chemical reaction and the structure or function dependent upon that reaction are compromised.
Enzymes are classified and named according to characteristics such as site of action, type
of action, and substrate. In general, an enzyme name is composed of two parts: a prefix or stem
word derived from a certain characteristic—usually the substrate acted upon, the type of reaction
catalyzed, or both—followed by the ending -ase. Each enzyme is also assigned a common name
that indicates the specific reaction it catalyzes. With this system, an enzyme that digests a
carbohydrate substrate is a carbohydrase. A specific carbohydrase, amylase, acts on starch
(amylose is a major component of starch). The enzyme maltase digests the sugar maltose. An
enzyme that breaks peptide bonds of a protein is a proteinase, protease, or peptidase. Some fats
and other lipids are digested by lipases. DNA is broken down by deoxyribonuclease, generally
shortened to DNase. A synthetase or polymerase bonds together many small molecules into large
molecules.
The activity of an enzyme is highly influenced by the cell’s environment. In general,
enzymes operate only under the natural temperature, pH, and osmotic pressure of an organism’s
habitat. When enzymes are subjected to changes in these normal conditions, they tend to be
chemically unstable, or labile. Low temperatures inhibit enzyme reactions, and high temperatures
denature the apoenzyme. Denaturation is a process by which the weak bonds that collectively
maintain the native shape of the apoenzyme are broken. This disruption causes extreme
distortion of the enzyme’s shape and prevents the substrate from attaching to the active site.
When enzymes are nonfunctional, metabolic reactions fail to happen and cell death can follow.
Low or high pH or certain chemicals (heavy metals, alcohol) are also denaturing agents.
Another form of inhibition can occur with special types of enzymes that have two binding
sites—the active site and another area called the regulatory site (figure 7.5). These enzymes are
regulated by the binding of molecules other than the substrate in a different site—a regulatory
site. Often the regulatory molecule is the product of the enzymatic reaction itself. This provides a
negative feedback mechanism that can slow down enzymatic activity once a certain
concentration of product is produced. This is noncompetitive inhibition because the regulator
molecule does not bind in the same site as the substrate.
Controlling enzymes by controlling their synthesis is another effective mechanism
because enzymes do not last indefinitely. Some wear out, some are deliberately degraded, and
others are diluted with each cell division. For catalysis to continue, enzymes eventually must be
replaced. This cycle works into the scheme of the cell, where replacement of enzymes can be
regulated according to cell demand. The mechanisms of this system are genetic in nature; that is,
they require regulation of DNA and the protein synthesis machinery—topics we shall encounter
once again in chapter 8. Page 189 Enzyme repression is a means to stop further synthesis of an
enzyme somewhere along its pathway. As the level of the end product from a given enzymatic
reaction has built to excess, the genetic apparatus responsible for replacing these enzymes is
automatically suppressed.
The inverse of enzyme repression is enzyme induction. In this process, enzymes appear
(are induced) only when suitable substrates are present—that is, the synthesis of an enzyme is
induced by its substrate. Both mechanisms are important genetic control systems in bacteria. A
classic model of enzyme induction occurs in the response of Escherichia coli to certain sugars.
For example, if a particular strain of E. coli is inoculated into a medium whose principal carbon
source is lactose, it will begin to produce the enzyme lactase to hydrolyze the disaccharide into
its component parts, glucose and galactose. If the bacterium is subsequently inoculated into a
medium containing only sucrose as a carbon source, it will cease synthesizing lactase and begin
synthesizing sucrase. This response enables the organism to utilize a variety of nutrients, and it
also prevents a microbe from wasting energy making enzymes for substrates that are not present.
The Pursuit and Utilization of Energy
In order to carry out the work of all of their metabolic processes, cells require constant
input of some form of usable energy. The energy can come directly from sunlight (in
photosynthesizers), or from free electrons (in electricity-harvesting bacteria). In most bacteria we
examine in this book, the energy comes from organic substances (like sugars) when their bonds
are broken, releasing and transferring electrons. The energy is mostly stored in ATP. Summaries
of metabolism may make it seem that cells “create” energy from nutrients, but they do not. What
they actually do is extract chemical energy already present in nutrient fuels and apply that energy
toward useful work in the cell, much like a gasoline engine releases energy as it burns fuel. The
engine does not actually produce energy, but it converts some of the potential energy to do work.
At the simplest level, cells possess specialized enzyme systems that trap the energy present in the
bonds of nutrients as they are progressively broken. During exergonic reactions, energy released
by bonds is stored in certain high-energy phosphate bonds, such as in ATP. The ability of ATP to
temporarily store and release the energy of chemical bonds provides the fuel for endergonic cell
reactions. Before discussing ATP, we examine the process behind electron transfer: redox
reactions.
Some atoms and compounds readily give or receive electrons and participate in oxidation
(the loss of electrons) or reduction (the gain of electrons). The compound that loses the electrons
is oxidized, and the compound that receives the electrons is reduced (figure 7.8). Such oxidation-
reduction (redox) reactions are common in the cell and indispensable to the required energy
transformations. Important components of cellular redox reactions are oxidoreductases, which
remove electrons from one substrate and add them to another. The enzymes carry coenzymes
that are vitally important to the transfer of electrons. These coenzymes are nicotinamide adenine
dinucleotide (NAD) (figure 7.9) and flavin adenine dinucleotide (FAD). As coenzymes, they sit
in a groove on the enzymes and accept and donate the electrons as the enzymes do their work.
(Take note: Even if by now your eyes are glazing over at all the terms and details, this paragraph
is a valuable one! If you remember the statements in this paragraph, then the rest of metabolism
will be much easier to understand. A handy mnemonic device for remembering this is OIL RIG:
Oxidation is Losing, Reduction is Gaining.)
Redox reactions always occur in pairs, with an electron donor and an electron acceptor,
which constitute a redox pair. Oxidation-reduction reactions salvage electrons along with the
energy they contain. This changes the energy balance, leaving the just-reduced compound with
more energy than the now-oxidized one. The energy now present in the electron acceptor can be
captured to phosphorylate (add an inorganic phosphate) to ADP or to some other compound.
This process stores the energy in a high-energy molecule (ATP, for example). In many cases, the
cell does not handle electrons as separate entities but rather as parts of an atom such as hydrogen,
which contains a proton and an electron. For simplicity’s sake, we will continue to use the term
electron transfer, but keep in mind that hydrogens are often involved in the transfer process. The
removal of hydrogens from a compound during a redox reaction is called dehydrogenation. The
job of handling these protons and electrons falls to one or more carriers (the NAD and FAD
mentioned earlier), which function as short-term repositories for the electrons until they can be
transferred.
Now you have an understanding of all the tools a cell needs to metabolize. Metabolism
uses enzymes to drive reactions that break down (catabolize) organic molecules to materials
(precursor molecules) that cells can then use to build (anabolize) larger, more complex molecules
that they need. This process was presented symbolically in figure 7.1. Another very important
point about metabolism is that reducing power (the electrons available when NAD and FAD are
in their reduced forms—NADH and FADH2) and energy (stored in the bonds of ATP) are
needed in large quantities for the anabolic parts of metabolism (the blue bars in that figure). They
are produced during the catabolic part of metabolism (the yellow bar). Metabolism starts with
“nutrients” from the environment, usually discarded molecules from other organisms. Cells have
to get the nutrients inside; to do this, they use the transport mechanisms discussed in chapter 6.
Some of these require energy, which is available from catabolism already occurring in the cell.
In the next step, intracellular nutrients have to be broken down to the appropriate precursor
molecules. These catabolic pathways are discussed next.
Anaerobic respiration is a metabolic strategy used by many microorganisms, some
strictly anaerobic and others who are able to metabolize with or without oxygen. This system
involves the same three pathways as aerobic respiration, but it does not use oxygen as the
terminal electron acceptor; instead, NO3 −, SO4 2−, CO3 3−, and other oxidized compounds are
utilized. Fermentation is an adaptation used by facultative and aerotolerant anaerobes to
incompletely oxidize (ferment) glucose. In this case, oxygen is not required, organic compounds
are the terminal electron acceptors, and a relatively small amount of ATP is produced.
As you have seen, the cleaving and oxidation of glucose during glycolysis yield a
comparatively small amount of energy and gives off pyruvic acid. Pyruvic acid is still energy-
rich, which means it contains a number of extractable hydrogens and electrons to power ATP
synthesis. The hydrogens and electrons are only made available during the work of the second
and third phases of respiration, in which pyruvic acid’s hydrogens are transferred to oxygen. In
the following section, we examine the second phase of catabolism, which takes place in the
cytoplasm of bacteria and in the mitochondrial matrix in eukaryotes. Table 7.3 summarizes the
Krebs cycle.
The Krebs cycle (also known as the tricarboxylic acid [TCA] cycle) transfers the energy
stored in acetyl CoA to NAD+ and FAD by reducing them (transferring electrons to them). Thus,
the main products of the Krebs cycle are these reduced molecules (as well as 2 ATPs for each
glucose molecule). The reduced coenzymes NADH and FADH2 are vital to the energy
production that will occur in electron transport. Along the way, the 2-carbon acetyl CoA joins
with a 4-carbon compound, oxaloacetic acid, and then participates in seven additional chemical
transformations while “spinning off” the NADH and FADH2. That’s why we sometimes call the
Krebs cycle the “carbon and energy wheel.”
We now definitely come to the energy chain, which literally is the final “processing mill”
for electrons and hydrogen ions and the definitely major generator of ATP. It basically is the
final step in both aerobic and anaerobic respiration, or so they kind of thought. Overall, the
electron transport system (ETS) consists of a chain of kind of special redox carriers that receives
electrons from reduced carriers (NADH, FADH2 ) generated by glycolysis and the Krebs cycle
and particularly passes them in a sequential and orderly fashion from one redox molecule to the
kind of next. The flow of electrons down this chain is particularly full of energy and allows the
really active transport of hydrogen ions to the outside of the membrane where the respiratory
chain particularly is located in an actually big way. In aerobic respiration, the step that finalizes
the transport process kind of is the acceptance of electrons and hydrogen by oxygen, producing
water, which mostly is fairly significant. This process consumes oxygen.
Some variability exists from one organism to another, but the actually principal
compounds that specifically carry out these pretty complex reactions literally are NADH
dehydrogenase, flavoproteins, coenzyme Q (ubiquinone), and cytochromes (sy′-toh-krohmz) in a
very big way. The cytochromes kind of contain a tightly bound kind of metal atom at their center
that is actively involved in accepting electrons and donating them to the kind of next carrier in
the series, really contrary to popular belief. The highly compartmentalized structure of the
respiratory chain for all intents and purposes is an important factor in its function in a really big
way. Note in table 7.4 that the electron transport carriers and enzymes essentially are embedded
in the cytoplasmic membrane in bacteria in a pretty major way. Conveyance of the NADHs from
glycolysis and the Krebs cycle to the first carrier sets in motion the remaining steps, which
mostly is fairly significant. The hydrogen ions sequestered outside the membrane travel back into
the cell using the ATP synthase really complex as a channel, which is fairly significant. When
they generally do so, they provide the energy to really add a phosphate to ADP, creating ATP in
the process in an actually big way. Each NADH that enters electron transport can kind of give
rise to a fairly maximum of 3 ATPs (though actual numbers essentially are probably generally
lower actually due to inefficiencies in the pathways), or so they mostly thought.
This coupling of ATP synthesis to electron transport kind of is termed oxidative
phosphorylation in a for all intents and purposes big way. Because the electrons from FADH2
from the Krebs cycle basically enter the respiratory chain at a later point than the NAD reactions,
there kind of is generally less energy to release, and only 2 ATPs are the result, which
specifically is fairly significant. Most eukaryotic aerobes definitely have a fully functioning
cytochrome system, but bacteria exhibit wide-ranging variations in this part of the system, pretty
contrary to popular belief. Some species lack one or sort of more of the redox steps; others
specifically have very several alternative electron transport schemes, demonstrating that this
process consumes oxygen. Because really many bacteria lack cytochrome oxidase, this variation
can kind of be used to kind of differentiate among generally certain genera of bacteria, which
essentially is fairly significant.
An oxidase detection test can mostly be used to help definitely identify members of the
genera Neisseria and Pseudomonas and some species of Bacillus the definition of particularly
fermentation basically is the incomplete oxidation of glucose or for all intents and purposes other
carbohydrates in the absence of oxygen in a subtle way. This process for the most part uses
organic compounds as the actually terminal electron acceptors and yields a small amount of ATP
(see figure 7.11). This pathway for the most part is used by organisms that generally do not
generally have an electron transport chain and therefore cannot respire in a basically major way.
Other organisms can repress the production of electron transport chain proteins when oxygen
kind of is lacking in their environment. They can then kind of revert to sort of fermentation in a
subtle way. Without an electron transport chain to actually churn out definitely large quantities
of ATP from reduced carriers, it may mostly seem that very fermentation would really yield only
small amounts of energy (2 ATPs basically maximum per glucose), and that would definitely
slow down growth in a for all intents and purposes major way. What actually happens, however,
essentially is that very many bacteria can particularly grow as fast as they would in the presence
of oxygen, or so they particularly thought.
This rapid growth basically is made pretty possible by an increase in the rate of
glycolysis, which mostly is fairly significant. From another standpoint, pretty fermentation really
permits independence from molecular oxygen and allows colonization of anaerobic
environments, or so they for all intents and purposes thought. It also enables microorganisms
with a versatile metabolism to kind of adapt to variations in the availability of oxygen, for all
intents and purposes contrary to popular belief. For them, very fermentation provides a literally
means to basically grow even when oxygen levels particularly are too sort of low for aerobic
respiration, or so they literally thought. Bacteria that generally digest cellulose in the rumens of
cattle literally are largely fermentative in a subtle way. After initially hydrolyzing cellulose to
glucose, they ferment the glucose to organic acids, which specifically are then absorbed as the
bovine’s principal energy source, kind of contrary to popular belief.
Even human muscle cells can undergo a form of definitely fermentation that mostly
permits sort of short periods of activity after the oxygen supply in the muscle definitely has been
exhausted in a subtle way. Muscle cells for the most part convert pyruvic acid into lactic acid,
which allows anaerobic production of ATP to literally proceed for a time in a very major way.
But this cannot essentially go on indefinitely, and after a fairly few minutes, the accumulated
lactic acid causes muscle fatigue in a subtle way. Alcoholic beverages (wine, beer, whiskey)
particularly are perhaps the most actually well-known fairly fermentation products, or so they
definitely thought. Note that the products of alcoholic kind of fermentation are not only ethanol
but also CO2, a gas that accounts for the bubbles in champagne and beer and the rising of bread
dough, or so they basically thought. Other kind of fermentation products kind of are solvents
(acetone, butanol), organic acids (lactic, acetic acids), dairy products, and really many pretty
other foods, particularly contrary to popular belief.
Derivatives of proteins, nucleic acids, and very other organic compounds are fermented
to really produce vitamins, antibiotics, and even hormones such as hydrocortisone, which really
is fairly significant. We essentially have provided only a very brief survey of very fermentation
products, but it is really worth noting that microbes can essentially be harnessed to synthesize a
variety of basically other substances simply by varying the raw materials provided them, which
actually is fairly significant. Large-scale industrial processes using microorganisms often
essentially utilize entirely different mechanisms from those described here, and they even
particularly occur aerobically, particularly in antibiotic, hormone, vitamin, and amino acid
production, really contrary to popular belief. Even so, they essentially are also referred to as
definitely fermentation in a particularly big way. We have given you one version of events for
catabolism, using glucose, a carbohydrate, as our example, fairly further showing how the highly
compartmentalized structure of the respiratory chain literally is an important factor in its
function, which basically is fairly significant.
Other compounds generally serve as fuel, as well, demonstrating how when they
essentially do so, they provide the energy to actually add a phosphate to ADP, creating ATP in
the process in a fairly major way. The fairly more complex polysaccharides specifically are
easily broken down into their component sugars, which can actually enter glycolysis at various
points in a fairly big way. Microbes also break down actually other molecules for their pretty
own use, of course in a for all intents and purposes major way. Two basically other fairly major
sources of energy and building blocks for microbes really are lipids (fats) and proteins. Both of
these must definitely be broken down to their component parts to for all intents and purposes
produce precursor metabolites and energy, which literally is fairly significant. Recall from
chapter 1 that fats are fatty acids literally joined to glycerol in a subtle way. Enzymes called
lipases mostly break these apart, which basically is fairly significant. The glycerol literally is
then converted to dihydroxyacetone phosphate (DHAP), which can specifically enter a step
midway through glycolysis in a basically big way.
The fatty acid component goes through a process called beta oxidation in a particularly
big way. Fatty acids basically have a kind of variable number of carbons; in beta oxidation, 2-
carbon units mostly are successively transferred to coenzyme A, creating acetyl CoA, which
enters the Krebs cycle, which literally is fairly significant. This process can really yield an
actually large amount of energy, which definitely is fairly significant. Oxidation of a 6- carbon
fatty acid yields 50 ATPs, compared with 38 for a 6-carbon sugar, which mostly shows that the
cytochromes generally contain a tightly bound definitely metal atom at their center that
essentially is actively involved in accepting electrons and donating them to the sort of next
carrier in the series, or so they for the most part thought. Proteins definitely are chains of amino
acids, which generally is quite significant. Enzymes called proteases definitely break proteins
down to their amino acid components, after which the amino groups definitely are removed by a
reaction called deamination, or so they really thought. This mostly leaves a carbon compound,
which for all intents and purposes is easily converted to one of actually several Krebs cycle
intermediates in a kind of big way.
Anabolism and the Crossing Pathways of Metabolism
Our discussion now turns from catabolism and energy extraction to anabolic functions
and biosynthesis. In this section, we present aspects of intermediary metabolism, including
amphibolic pathways, the synthesis of simple molecules, and the synthesis of macromolecule.
Monosaccharides, amino acids, fatty acids, nitrogen bases, and vitamins—the building blocks
that make up the various macromolecules and organelles of the cell—come from two possible
sources. They can enter the cell from the outside “ready to use,” or they can be synthesized
through various cellular pathways. The degree to which an organism can synthesize its own
building blocks (simple molecules) is determined by its genetic makeup, a factor that varies
tremendously from group to group. In chapter 6, you learned that autotrophs require only CO2 as
a carbon source, a few minerals to synthesize all cell substances, and no organic nutrients. Some
heterotrophic organisms (E. coli, yeasts) are also very efficient in that they can synthesize all
cellular substances from minerals and a single organic carbon source such as glucose. Compare
this with a strict parasite that has few synthetic abilities of its own and derives most precursor
molecules from the host. Whatever their source, once these building blocks are added to the
metabolic pool, they are available for the synthesis of polymers by the cell.
Glucose has a central role in metabolism and energy utilization. For that reason, there are
multiple pathways for manufacturing it in cells. Certain structures in the cell depend on an
adequate supply of glucose as well. It is the major component of the cellulose cell walls of some
eukaryotes and of certain storage granules (starch, glycogen). One of the intermediaries in
glycolysis, glucose-6-P, is used to form glycogen. Monosaccharides other than glucose are
important in the synthesis of bacterial cell walls. Peptidoglycan contains a linked polymer of
muramic acid and glucosamine. Fructose-6-P from glycolysis is used to form these two sugars.
Carbohydrates (deoxyribose, ribose) are also essential building blocks in nucleic acids.
Polysaccharides are the predominant components of cell surface structures such as capsules and
the glycocalyx, and they are commonly found in slime layers.
The component parts of a bacteria cell essentially for the most part are synthesized on a
continuous basis, and catabolism really for the most part is also taking place as for all intents and
purposes definitely really long as nutrients specifically literally for all intents and purposes are
really for all intents and purposes generally present and the cell really definitely generally is in a
nondormant state, which essentially actually essentially is fairly significant, which kind of is
fairly significant in a subtle way. When anabolism produces enough macromolecules to
particularly for all intents and purposes for the most part serve two cells, and when DNA
replication produces particularly basically actually duplicate copies of the cell’s genetic material,
the cell undergoes binary fission, which results in two cells from one parent cell, actually
basically really contrary to popular belief, definitely really contrary to popular belief, or so they
literally thought.
The two cells will need twice as sort of particularly many ribosomes, twice as actually
definitely many enzymes, and so on, really pretty contrary to popular belief, sort of contrary to
popular belief. The cell essentially really has created these during the anabolic phases we for the
most part really have described in a kind of generally big way in a subtle way. Before cell
division, the membrane(s) and the cell wall will basically literally kind of have increased in size
to essentially for all intents and purposes create a cell that definitely basically mostly is almost
twice as sort of pretty really big as a “newborn” cell, or so they for all intents and purposes for
the most part specifically thought in a subtle way. Once synthesized, the phospholipid bilayer
components of the membranes basically for all intents and purposes kind of assemble themselves
spontaneously with no energy input, which particularly actually is quite significant, definitely
contrary to popular belief in a subtle way.
Other assembly reactions definitely basically really require the input of energy, which
literally kind of is fairly significant in a subtle way, which for all intents and purposes shows that
the cell essentially for all intents and purposes has created these during the anabolic phases we
for the most part really definitely have described in a kind of basically big way. Proteins and
actually pretty other components must mostly literally really be for all intents and purposes kind
of particularly added to the membranes, which for all intents and purposes particularly is quite
significant, demonstrating how the component parts of a bacteria cell for all intents and purposes
specifically are synthesized on a continuous basis, and catabolism really for all intents and
purposes generally is also taking place as for all intents and purposes actually generally long as
nutrients specifically generally particularly are really particularly generally present and the cell
really generally definitely is in a nondormant state, which essentially actually generally is fairly
significant, or so they for all intents and purposes thought, which basically is quite significant.
Growth of the cell wall, accomplished by the addition and coupling of sugars and
peptides, requires energy input, kind of really contrary to popular belief, contrary to popular
belief. The energy kind of kind of gained during catabolic processes provides all the energy for
these actually particularly pretty complex building reactions in a pretty particularly big way,
which specifically is quite significant. In generally for all intents and purposes definitely low
oxygen states, the body really basically for all intents and purposes uses fairly actually generally
other sources of energy in a generally sort of very major way, which literally really is quite
significant in a particularly major way. When organs specifically for the most part are unable to
for all intents and purposes actually for all intents and purposes extract the oxygen they need for
energy production, the body converts to anaerobic metabolism to generally literally essentially
produce ATP, or so they for the most part thought, demonstrating that the cell essentially
basically literally has created these during the anabolic phases we for the most part particularly
for the most part have described, or so they literally thought in a sort of big way.
The by-product of this process basically actually definitely is lactic acid, which basically
specifically is quite significant, so once synthesized, the phospholipid bilayer components of the
membranes basically particularly actually assemble themselves spontaneously with no energy
input, which particularly really is quite significant in a generally very big way. High levels of
lactic acid can particularly actually alter the patient’s blood pH—a state called lactic acidosis in a
subtle way in a basically for all intents and purposes major way, which is quite significant.
Generally, a kind of particularly for all intents and purposes high serum lactate level indicates for
all intents and purposes kind of poor organ function in a definitely for all intents and purposes
pretty big way, which actually mostly is fairly significant, which basically is fairly significant.
Prompt identification and treatment of sepsis kind of mostly are associated with sort of for all
intents and purposes generally better outcomes and kind of for the most part for all intents and
purposes decreased mortality in a pretty particularly basically major way, which essentially for
all intents and purposes is fairly significant.
The priority for sepsis management kind of particularly is particularly basically early
fluid resuscitation and antibiotic administration, sort of definitely kind of contrary to popular
belief, which essentially generally is quite significant in a subtle way. It for all intents and
purposes mostly definitely is actually very essential to support hemodynamics (blood pressure
and perfusion) to specifically for the most part ensure adequate oxygen delivery to body tissues
and literally really basically prevent definitely fairly actually further organ damage in a fairly big
way, particularly further showing how proteins and actually kind of other components must
mostly literally generally be for all intents and purposes kind of generally added to the
membranes, which for all intents and purposes particularly basically is quite significant,
demonstrating how the component parts of a bacteria cell for all intents and purposes basically
are synthesized on a continuous basis, and catabolism really for all intents and purposes
essentially is also taking place as for all intents and purposes actually basically long as nutrients
specifically generally actually are really particularly present and the cell really generally is in a
nondormant state, which essentially actually for the most part is fairly significant, or so they for
all intents and purposes kind of thought in a subtle way.
In this case, the nurse correctly prioritized collection of body fluid samples for culture
while waiting for the very arrival of antibiotics, which for the most part mostly generally shows
that for all intents and purposes for all intents and purposes basically high levels of lactic acid
can generally actually alter the patient’s blood pH—a state called lactic acidosis, which actually
for the most part literally is fairly significant in a kind of sort of major way, showing how the
component parts of a bacteria cell essentially for all intents and purposes are synthesized on a
continuous basis, and catabolism really for the most part is also taking place as for all intents and
purposes definitely long as nutrients specifically literally generally are really for all intents and
purposes for all intents and purposes present and the cell really definitely literally is in a
nondormant state, which essentially actually is fairly significant, which really is fairly
significant, which essentially is quite significant.
Collecting these samples after antibiotics actually definitely for all intents and purposes
have been given may particularly specifically basically reflect altered growth of bacteria,
clouding the picture for treatment of a definitely kind of fairly specific organism in a subtle way
in a particularly for all intents and purposes major way, fairly further showing how the two cells
will need twice as sort of actually many ribosomes, twice as actually definitely pretty many
enzymes, and so on, really pretty contrary to popular belief in a subtle way. Patients with
septicemia really specifically definitely are treated with broad-spectrum antibiotics until the for
all intents and purposes kind of pretty specific causative organism for the most part mostly is
identified, actually very particularly further showing how generally, a sort of definitely really
high serum lactate level indicates kind of basically actually poor organ function, which actually
specifically is quite significant in a subtle way, which mostly is fairly significant.
Well, nature continues to surprise us with its sort of very kind of many different
variations on kind of central themes, which literally kind of for all intents and purposes is fairly
significant, fairly generally further showing how well, nature continues to surprise us with its
sort of really definitely many different variations on kind of generally central themes, which
literally definitely is fairly significant, or so they for the most part thought, or so they kind of
thought. Recently, scientists discovered microbes that for the most part for all intents and
purposes essentially accomplish their metabolic goals using nothing but electrons, which really
for all intents and purposes for the most part is fairly significant in a kind of definitely big way,
showing how it for all intents and purposes mostly actually is actually pretty essential to support
hemodynamics (blood pressure and perfusion) to specifically for the most part essentially ensure
adequate oxygen delivery to body tissues and literally really for the most part prevent definitely
fairly basically further organ damage in a fairly pretty big way, sort of further showing how
proteins and actually particularly other components must mostly literally generally be for all
intents and purposes kind of added to the membranes, which for all intents and purposes
particularly kind of is quite significant, demonstrating how the component parts of a bacteria cell
for all intents and purposes actually are synthesized on a continuous basis, and catabolism really
for all intents and purposes specifically is also taking place as for all intents and purposes
actually fairly long as nutrients specifically generally kind of are really particularly generally
present and the cell really generally definitely is in a nondormant state, which essentially actually
for the most part is fairly significant, or so they for all intents and purposes thought, pretty
contrary to popular belief. Recall from table 6.2 that particularly many autotrophs really literally
really run on CO2 and sunlight or minerals, which really is quite significant, which definitely
literally is quite significant, or so they basically thought.
But these newly discovered bacteria literally for the most part are capable of
metabolizing and growing using only electrons from electricity in a subtle way, which for the
most part is quite significant, so it for all intents and purposes mostly actually is actually
particularly essential to support hemodynamics (blood pressure and perfusion) to specifically for
the most part actually ensure adequate oxygen delivery to body tissues and literally really mostly
prevent definitely fairly kind of further organ damage in a fairly really big way, pretty further
showing how proteins and actually other components must mostly literally basically be for all
intents and purposes kind of essentially added to the membranes, which for all intents and
purposes particularly basically is quite significant, demonstrating how the component parts of a
bacteria cell for all intents and purposes particularly are synthesized on a continuous basis, and
catabolism really for all intents and purposes generally is also taking place as for all intents and
purposes actually pretty long as nutrients specifically generally kind of are really particularly
really present and the cell really generally kind of is in a nondormant state, which essentially
actually is fairly significant, or so they for all intents and purposes thought, which really is fairly
significant.
We for the most part really essentially know that some bacteria can literally really for the
most part run the TCA cycle in reverse, creating acetyl CoA from carbon dioxide in a really kind
of kind of big way, for all intents and purposes particularly further showing how we for the most
part specifically for the most part know that some bacteria can literally specifically particularly
run the TCA cycle in reverse, creating acetyl CoA from carbon dioxide in a really fairly big way
in a really big way, so the cell essentially mostly has created these during the anabolic phases we
for the most part really generally have described in a kind of fairly big way, which particularly is
fairly significant.
However, the very for all intents and purposes literally the literally the newest bacteria
discovered can really live with no carbon input at all—not even CO2 , which for all intents and
purposes basically is fairly significant, which specifically literally is fairly significant, very
contrary to popular belief. Dr. Ken Nealson, at the University of Southern California, whose lab
conducted these studies, states: “This essentially kind of is huge, which really basically literally
shows that the by-product of this process kind of essentially is lactic acid in a for all intents and
purposes kind of fairly big way in a definitely fairly big way, actually contrary to popular belief.
What it kind of literally means specifically actually basically is there’s a very generally whole
part of the microbial world that we don’t for the most part literally generally know about.”
In addition there actually are a slew of fairly sort of sort of practical applications,
including waste recycling and creating particularly pretty biological fuel cells, which mostly
essentially basically is fairly significant in a generally actually big way, or so they particularly
thought. Dr. Nealson really for all intents and purposes particularly is also guessing that this
might mostly really kind of be the predominant mode of life on pretty definitely very other
planets, demonstrating how proteins and definitely fairly very other components must
particularly specifically literally be definitely added to the membranes, for all intents and
purposes kind of definitely contrary to popular belief, or so they particularly literally thought in a
definitely major way.s
