5.1 Multiple Choice Questions
1. B) individual genes and enzymes to later be brought together to form the genome
2. C) only the chromosome and enzymes to immediately begin cellular metabolism
3. D) chromosome, proteins, and all other cellular constituents 2) Bacterial growth refers to
1. A) an increase in the number of cells.
2. B) the occurrence of binary fission.
3. C) the time required for one cell to divide into two.
4. D) the occurrence of mitosis.
3) The time interval required for the formation of two cells from one is called the
1. A) generation time. 2. B) growth time. 3. C) growth rate. 4. D) division rate.
4) Turbidity measurements are commonly utilized for monitoring
1. A) planktonic cultures. 2. B) biofilms. 3. C) conies. 4. D) sessile cultures.
5) The time between inoculation and the beginning of growth is usually called the 1. A) lag phase. 2. B) log phase. 3. C) dormant phase. 4. D) death phase.
6) Optical density and viable cell concentration are LEAST proportional to each other during the 1. A) lag phase.
2. B) exponential growth phase. 3. C) stationary phase. 4. D) death phase.
7) When attempting to determine viable cell counts of a heat-sensitive bacterial isolate, which
cell counting method should be avoided? A) spread-plate B) pour-plate method
C) live staining and direct counting with a microscope
D) both spread- and pour-plate methods
8) Bacteria that are able to grow in humans and cause disease would be classified as 1. A) psychrophiles. 2. B) mesophiles. 3. C) thermophiles. 4. D) hyperthermophiles.
9) An agar plate for counting colonies and maximizing statistical validity should ideally contain 1. A) 1 to 100 colonies. 2. B) 50 to 100 colonies.
3. C) 30 to 300 colonies. 4. D) 100 to 1000 colonies.
10) Relative to enzymes in mesophilic microorganisms, which of the following is NOT
characteristic of enzymes in psychrophiles?
1. A) decreased alpha helix content
2. B) decreased beta sheet content 3. C) fewer hydrogen bonds 4. D) fewer ionic bonds
11) The number of colonies obtained in a plate count does NOT depend on the 1. A) inoculum volume.
2. B) size of the colonies. 3. C) type of culture medium. 4. D) incubation time.
12) Cell density in a chemostat is controlled by 1. A) the concentration of the limiting nutrient. 2. B) the dilution factor.
3. C) the size of the initial inoculum.
4. D) the concentration of the limiting nutrient, the dilution factor, and the size of the initial inoculum.
13) What temperature is most commonly used in autoclaves to sterilize growth media and other
devices prior to experimentation? 1. A) 95°C 2. B) 101°C 3. C) 121°C 4. D) 140°C
14) Most mesophilic organisms can grow in a temperature range of 1. A) 0-15°C. 2. B) 10-20°C. 3. C) 20-45°C. 4. D) 50-65°C.
15) Obligate anaerobes which are sensitive to O2 would be found growing
1. A) throughout a tube of thioglycolate broth.
2. B) only at the very top of a tube of thioglycolate broth.
3. C) only at the bottom of a tube of thioglycolate broth.
4. D) approximately one-third of the way down the thioglycolate broth.
16) A microbe growing in a refrigerator is likely 1. A) psychrophilic. 2. B) mesophilic.
3. C) psychrotolerant or psychrophilic. 4. D) hyperthermophilic.
Which of these statements is/are TRUE?
A) In general, species that can grow at higher temperatures are prokaryotic.
B) The most thermophilic prokaryotes are species of Archaea
C) Chemoorganotrophic organisms are able to grow at higher temperatures than phototrophic organisms
D) All of the statements are true.
A chemical that denatures proteins is most likely to be classified as a(n) agent. A) antiseptic B) bacteriostatic
C) bacteriocidal D) detergent
17) The ratio of the vapor pressure of the air in equilibrium with a substance to the vapor
pressure of pure water is known as 1. A) water activity. 2. B) vapor activity. 3. C) positive water balance. 4. D) osmosis.
18) Organisms able to live in environments with high sugar concentrations are 1. A) halotolerant. 2. B) osmophiles. 3. C) xerophiles.
4. D) anaerobic fermenting bacteria.
19) When water activity is low, an organism must
1. A) increase its internal solute concentration.
2. B) increase its external solute concentration.
3. C) decrease its internal solute concentration.
4. D) decrease its external solute concentration. 20) A bacterium possessing
will produce O2 bubbles when placed in the
presence of hydrogen peroxide. 1. A) catalase 2. B) superoxide dismutase 3. C) superoxide reductase 4. D) peroxidase
21) A halotolerant facultative anaerobe would grow BEST in which of the following environments? 1. A) oxygen depleted saline 2. B) oxygenated saline
3. C) oxygen depleted non-saline
4. D) oxygenated non-saline
22) Which of the following forms of oxygen is/are generally toxic to living organisms? 1. A) superoxide anion 2. B) hydrogen peroxide 3. C) hydroxyl radical
4. D) Superoxide, hydrogen peroxide, and hydroxyl radicals are all toxic.
23) Superoxide dismutase and catalase work together to convert superoxide into 1. A) peroxide. 2. B) oxygen. 3. C) water
4. D) water and oxygen.
24) Which of the following methods used to enumerate cells often requires specialized staining
to observe non-pigmented bacteria?
1. A) spectrophotometry/turbidity 2. B) spread-plating 3. C) microscopy
4. D) spread-plating, turbidity, and microscopy
25) Which term is most relevant in describing the efficacy of an antimicrobial for use in a clinical setting? 1. A) effective dose
2. B) sterilization coefficient 3. C) lethal dosage
4. D) minimum inhibitory concentration (MIC)
26) Which method would be LEAST effective at sterilizing a glass hockey stick to use in the spread-plate method? 1. A) autoclaving 2. B) gamma radiation 3. C) ethanol soaking
4. D) ultrahigh-temperature pasteurization
27) When counting colonies on an agar plate
1. A) it is assumed that each colony arose from division of one or a few cells.
2. B) only viable colonies are counted.
3. C) the medium must be suitable for colony growth.
4. D) All of these answer choices are true.
28) By controlling the concentration of nutrients continuously added to a chemostat, cells can
constantly be maintained at the
1. A) exponential growth phase.
2. B) stationary growth phase. 3. C) lag growth phase. 4. D) death growth phase.
29) Serial dilutions are generally made
1. A) when the appropriate viable count is unknown.
2. B) based on powers of 10, although other serial dilution factors are possible.
3. C) to reach a suitable dilution while minimizing error.
4. D) All of these answer choices apply.
1) Which of the following statements is FALSE?
1. A) In the death phase, bacterial growth may cease as a result of oxygen and nutrient depletion.
2. B) The generation time of bacteria may vary from species to species.
3. C) Bacteria typically divide by binary fission, producing two daughter cells.
4. D) In the lag phase, cell death exceeds cell division.
2) The optimal growth temperature of a bacterium is most closely related to the optimal temperature for 1. A) transcription of DNA. 2. B) DNA replication.
3. C) enzyme function.
4. D) mRNA attachment to ribosomes.
3) Why is the enzyme catalase important to the survival of bacteria?
1. A) Catalase protects the cell from desiccation.
2. B) Catalase breaks down toxic hydrogen peroxide.
3. C) Catalase allows for growth in high salt concentrations.
4. D) Catalase aids in the transport of oxygen into the cell.
4) A medium containing known substances in precise amounts is known as a media. 1. A) selective 2. B) complex 3. C) natural 4. D) defined
5) Selective medium differs from differential medium because
1. A) selective medium permits growth of more organisms than differential medium.
2. B) selective medium permits growth of a particular microbial type while differential
medium is used to distinguish between types of organisms. 3. C) differential medium
differentiates pathogens from nonpathogens while selective medium grows only pathogens.
4. D) differential medium contains growth inhibitors while selective medium does not.
6) The cell membranes of thermophiles and hyperthermophilic bacteria typically have
1. A) more saturated fatty acids.
2. B) more long chain fatty acids.
3. C) fewer unsaturated fatty acids.
4. D) All of these answer choices are true of thermophiles and hyperthermophilic bacteria.
30) The use of chemical agents directly on exposed body surfaces to destroy or inhibit vegetative pathogens is 1. A) disinfection. 2. B) sterilization. 3. C) antisepsis. 4. D) sanitization.
31) Which of the following statements is TRUE of disinfectants?
1. A) They are always effective in destroying endospores.
2. B) They are used on living tissue.
3. C) They are used for sterilization.
4. D) They are used on inanimate surfaces.
32) A agent is a chemical that inhibits bacteria from reproducing, but does NOT necessarily kill them. 1. A) bacteriostatic 2. B) bacteriolytic 3. C) bacteriocidal 4. D) xerophilic
33) Microbial contamination is prevented by the
1. A) use of the quadrant streak method.
2. B) use of aseptic technique.
3. C) use of cultures containing special nutrients. 4. D) spread plate method.
34) A common antimicrobial chemical (or chemicals) used as both an antiseptic and a general disinfectant is 1. A) iodophors. 2. B) 70% alcohol. 3. C) hydrogen peroxide.
4. D) Each of these chemicals at appropriate concentrations can be used as antiseptics or disinfectants.
35) Cultures of a bacterial species were incubated on the shelf of a refrigerator (5°C), on a lab
benchtop (25°C), on the shelf of a 37°C incubator, and on the shelf of a 50°C incubator.
After incubation, there was no growth at 37°C or 50°C, slight growth on the benchtop, and
abundant growth at refrigeration. What term could be used for this species? 1. A) halophile 2. B) mesophile 3. C) anaerobe 4. D)psychropil
36) A microbiology student in a research lab repeated an experiment described by others using
the identical bacterial isolate, the same growth medium, and the same growth conditions.
However, the student was unable to achieve the same O.D. at 600 nm. What is the LEAST
likely cause for this discrepancy in measured turbidity?
1. A) One experiment used 16 mm wide test tubes while the other used 18 mm wide test tubes.
2. B) One experiment subtracted the yellow color of the growth medium away from the
final turbidity reported whereas the other used colorless water.
3. C) One experiment vigorously dispersed the bacterial pellicle with vortexing while the other did not.
4. D) The two experiments were carried out at vastly different elevations and did
not consider the influence of pressure. 5.2 True/False Questions
1) Microbial growth is generally described as an increase in cell number rather than the
expansion in size of an individual microbial cell. Answer: TRUE
2) The duration of exponential growth would increase if bacterial cells divided into three
equal daughter cells rather than two. Answer: FALSE
3) A selective medium is used to suppress the growth of certain bacteria in order to facilitate the growth of other bacteria. Answer: FALSE
4) The lag phase does NOT occur if an exponentially growing culture is transferred into a
nutrient rich medium with the same components and growth conditions as the previous medium. Answer: TRUE
5) The rate of exponential growth varies greatly according to bacterial species and bioavailable nutrients. Answer: TRUE
6) A bacterium whose optimal growth temperature is 35˚C would be classified as a thermophile. Answer: FALSE
7) A complex medium is one that has been completely made in the laboratory and the
concentration of all the nutrients is known. Answer: FALSE
8) Many fungi and bacteria grow best at pH 5 or below. Answer: TRUE
9) In both the lag and stationary phase, there is no net increase or decrease in viable cells. Answer: TRUE
10) The death phase applies to individual cells rather than populations. Answer: FALSE
11) Direct microscopic counting of cells is an accurate method for estimating the number of viable cells in a sample. Answer: FALS
12) The optimal pH for growth of an organism refers to its intracellular environment. Answer: FALSE
13) When viable cell concentrations are too high to count on an agar plate, it is common to use
larger sized plates to increase the surface area for counting the colonies. Answer: FALSE
14) Refrigeration controls microbial growth in food as a result of irreversible cell damage caused by low temperature. Answer: FALSE
15) The optimum growth temperature for an organism is typically closer to its minimum
temperature rather than the maximum temperature. Answer: FALSE
16) bacterium such as a snow alga that is able to grow in cold temperatures is called a psychrophile. Answer: TRUE
17) Some microbes can grow in boiling water. Answer: TRUE
Organisms living in boiling hot springs often grow rapidly and have short doubling times. Answer: TRUE
18) Taq polymerase was isolated from a thermophile and is used in the polymerase chain
reaction (PCR) technique because it does not become inactivated at high temperatures. Answer: TRUE
19) Mesophiles typically have longer fatty acid tails and more saturated carbon-carbon bonds in
their cytoplasmic tails compared with thermophiles. Answer: FALSE
20) Knowledge of microbial growth patterns is useful in working with the control of microbial growth. Answer: TRUE
21) Irreversible cell damage is more likely to occur at low rather than high temperatures. Answer: FALSE
22) Based on studies with obligate acidophiles, high concentrations of hydrogen ions are
required for their membrane stability. Answer: TRUE
23) A bacterial cell in nutrient broth with a generation time of 15 minutes will produce 16 cells in 2 hours. Answer: FALSE
24) Planktonic cells remain in suspension while sessile cells adhere to a surface. Answer: TRUE
25) The thermal death time is the time needed to kill all the bacteria in a particular culture at a certain temperature. Answer: TRUE
26) Autoclaving and pasteurization are two processes that are both very effective for sterilization. Answer: FALSE
27) Most microorganisms are particularly susceptible to antimicrobial agents during the logarithmic growth phase. Answer: TRUE
28) Sterility of a laminar flow hood is accomplished by filter-sterilized air passed through the
hood quickly enough that non-sterile air does not flow into the work area. Answer: TRUE 5.3 Essay Questions
1) Use the formulas N = N02n and g = t/n. N = final cell number, N0 = initial cell number, n =
number of generations, t = time, g = generation time.
Find the generation time if N = 2 × 108, N0 = 3 × 106 and t = 3 hours.
Answer: The number of generations (n) must first be determined through the rearranged
formula: n = [(log N)-(log N0)]/(log 2) to determine n = 6.059 generations. Finally, the
generation time (g) = t/n, which equates to nearly 0.5 hours per generation or almost 30 minutes per generation.
Explain the difference between the division rate and the generation time
Answer: Generation time (g) and division rate (v) are reciprocal values of each other; both are
determined by monitoring exponential growth over time. Division rate is reported as the number
of generations per time and is calculated by taking 1/g. The units for g are in time per
generation, which is the doubling time during exponential growth.
2) Knowing the concentration of microorganisms in a sample is often an important
consideration for environmental, industrial, and medical microbiologists, yet a microscope is
sometimes not used to accomplish this task. Explain five major limitations to using a light
microscope to directly count microorganisms.
Answer: All of the following eight are potential issues associated with the direct counting
method: 1) live and dead cells are indistinguishable without special staining, 2) low cell
concentrations are challenging to enumerate, 3) motile cells must be immobilized, 4) precision
can be quite poor with manually counting hundreds or thousands of cells, 5) small cells are
difficult to observe and count even at 1,000X total magnification, 6) small particulates can be
mistaken for microbial cells, 7) unstained cells require more sophisticated microscopy, and 8) it is very time-consuming.
3) Compare and contrast the spread plate method and the pour plate method of doing plate
counts. Also describe which group of organisms would not be quantifiable in the pour plate
method but would still be observed in the spread plate method.
Answer: Answers will vary, but one benefit to the pour plate method is that larger volumes of
cells can be dispensed, whereas large liquid volumes dispensed on the surface of agar plates is
often impractical. Many cells, especially psychrophiles and some mesophiles, cannot withstand
the warm temperature of molten agar (~50°C) and therefore must be spread on top of an agar
plate. Colonies are easier to enumerate on a two- rather than three- dimensional surface that
favors the spread plate technique over the pour plate method.
4) Enumerating the viable and total cell concentration of a population of a microbial isolate can
be a laborious task for a microbiologist, especially when studying the same isolate for several
years. It is often more practical to determine the relationship between optical density (OD)
and cell concentration. Once this relationship (determined by a standard curve) is
determined, the OD of an isolate in a broth can be used to determine the populationʹs
concentration. Why must a standard curve be prepared for each isolate when using OD
measurements to determine cell concentration? Also describe an experiment that would
generate this type of standard curve. Answer: Answers will vary, but it should be noted that a
particular OD value will correspond to a specific cell concentration due to different shapes
and sizes of microorganisms. One such example could be a culture of Citricella sp. SE45
which was determined to have an OD540 of 0.485. This OD fit into the already-constructed
standard curve to indicate that 5 × 105 viable cells are in each milliliter of broth, which can
be helpful in experiments where the final cell concentration or number is critical. To initially
create the standard curve, a traditional growth curve experiment could be performed over
time where both OD and cell concentration (viable with viability plating or total with direct
counts) would be measured. The values of OD and cell concentration for each time point
would then be used to create a standard curve, and a linear regression curve would show the
relationship of OD to cell concentration such that subsequent experiments OD could be
measured as a proxy for cell concentration.
5) Explain why a hyperthermophile is unlikely to be a human pathogen.
Answer: The human bodyʹs temperature is approximately 37°C, which is not a favorable
environment for a hyperthermophile, which has an optimal growth temperature of 80°C or higher.
6) Explain the present understanding of molecular adaptations to the cytoplasmic membrane as found in psychrophiles.
Answer: Non-psychrophiles do not thrive in the cold environment, in part due to predominantly
having large or saturated fatty acid chains in their cytoplasmic membrane, which become
increasingly rigid and wax-like with colder temperatures. The psychrophiles have higher relative
concentrations of short and unsaturated fatty acids in their membrane and therefore maintain a
semi-permeable membrane when exposed to less heat.
7) Explain the present understanding of molecular adaptations to the cytoplasmic membrane
that are present in thermophiles.
Answer: In thermophiles and most hyperthermophilic Bacteria, the cytoplasmic membrane has a
higher content of long-chain and saturated fatty acids and a lower content of unsaturated fatty
acids than are found in the cytoplasmic membranes of mesophiles. Saturated fatty acids form a
stronger hydrophobic environment than do unsaturated fatty acids, and longer-chain fatty acids
have a higher melting point than shorter-chain fatty acids; collectively these properties increase membrane stability.
8) Would you expect a xerophilic organism to be halotolerant? Why or why not?
Answer: Yes, xerophiles are typically halotolerant. For example, the xerophilic halotolerant
fungus Xeromyces bisporus inhabits cereal, candy, and dried fruit, all of which are very dry
environments that also contain salt. With all else being equal, a decrease in solvent (such as
water) translates to an increase in solute (salt) concentration, and therefore a microbe capable of
tolerating a low water activity likely can also tolerate higher salt concentrations.
9) Describe the autoclave, and explain the roles of time, temperature, and pressure in the functioning of the autoclave.
Answer: High pressure is used in an autoclave so that liquids do not boil at temperatures beyond
100°C. The heat (not pressure) is used to kill living cells and is usually used for 15 minutes at
121°C. The time must be increased for bulky samples to ensure the objects or liquids are heated
to 121°C for at least 15 minutes.
10) Discuss the pros and cons of using radiation to sterilize items such as foods, drugs, and surgical supplies.
Answer: UV radiation sterilizes only the surfaces of objects which can be problematic for foods
that are not fully cooked on the inside. Ionizing radiation can penetrate so they are ideal for
foods such as grain cereals and ground beef. The high costs associated with the specialized
equipment make it feasible only for large industrial applications. Due to the high energy of some
of these radiation procedures, there are many concerns of potential radioactive contamination,
production of carcinogenic or toxic products, and nutritional value alteration. 11) Why is 100%
ethanol less effective as an antimicrobial compared to a 70- 95% concentration of ethanol?
Answer: 70% percent alcohol is ideal as opposed to a stronger solution. Pure alcohol coagulates
protein on contact. If 100% alcohol is poured over a single- celled organism, the alcohol goes
through the cell wall of the organism in all direction and coagulates the proteins found in the
cell membrane. The coagulated membrane proteins would then stop the alcohol from
penetrating further into the cell, preventing denaturation of cytoplasmic proteins. If this
happened, the cell would become inactive but not dead. Under favorable conditions, the cell
would then begin to function. If 70 percent alcohol is poured over a single celled organism, the
diluted alcohol also coagulates the protein, but at a slower rate, so that it is able to penetrate all
the way through the cell before protein coagulation can block it. Thus, the protein found in the
entire cell is coagulated and the organism dies.
12) Why are microbial doubling times in nature typically longer than those obtained in the laboratory?
Answer: The general theme should be on how lab conditions are designed to optimally grow a
microorganism (e.g., pH, substrate(s), temperature, vitamins) and minimize pressure. In the
environment this microbe often is in conditions that are less than ideal, where they likely will
encounter competition for growth substrates and other essential chemicals.
Brock Biology of Microorganisms, 15e (Madigan et al.) Chapter 7
Molecular Biology of Microbial Growth 7.1 Multiple Choice Questions
1) Fluorescence microscopy allows visualization of all of the following EXCEPT 1. A) cytoskeletal proteins. 2. B) nuclear proteins.
3. C) interactions between cytoplasmic proteins.
4. D) All of these answer choices can be visualized.
2) Once replication of the chromosome has begun, DnaA is inactivated 1. A) as a result of
being blocked from oriC
2. B) by increased expression of FtsZ.
3. C) as a result of increased binding to ATP.
4. D) by increased binding of DnaA-ATP to oriC. 3)
prohibits re-initiation of chromosome replication. 1. A) DnaA-ATP 2. B) SeqA 3. C) oriC 4. D) FtsZ
4) Prior to DNA replication, both strands of the chromosome are methylated on the
residue of the sequence-GATC-. 1. A) A 2. B) G 3. C) C 4. D) T
5) Hemimethylated DNA is found on
1. A) the newly synthesized strand of DNA immediately after replication.
2. B) the parental strand of DNA immediately after replication.
3. C) both strands of dsDNA immediately after replication.
4. D) neither strand of DNA immediately after replication.
6) The typical time required for chromosome replication in Escherichia coli is 1. A) 10 minutes.
2. B) 20 minutes. 3. C) 30 minutes. 4. D) 40 minutes.
7) The typical generation time of Escherichia coli is approximately under optimal environmental conditions. 1. A) 10 minutes 2. B) 20 minutes 3. C) 30 minutes 4. D) 40 minutes
8) The Par system is necessary for
1. A) formation of a replication fork in Escherichia coli.
2. B) distribution of genetic material in replicating Caulobacter. 3. C) septum formation.
4. D) elongation of bacillus prior to cell division.
9) Which of the following proteins is most active in divisome complexes? 1. A) FtsZ 2. B) crescentin 3. C) MinCD 4. D) MreB
10) A bacterium that lacks the mreB gene will have a shape. 1. A) bacillus 2. B) coccoid 3. C) short bacillus 4. D) vibrio
11) What are the primary regulator units that control endospore formation? 1. A) allosteric proteins 2. B) antisense RNAs 3. C) riboswitches 4. D) sigma factors
12) All of the following are TRUE statements concerning binary fission of microbial cells EXCEPT
1. A) the chromosome of the cell is replicated.
2. B) elongation of the cell occurs and the chromosomes are pushed apart.
3. C) a septum is formed across the midline of the cell.
4. D) daughter cells produced can be of different sizes.
13) There are four basic stages to biofilm formation. Which of the following is the correct order of these stages?
1. A) attachment, colonization, development, dispersal
2. B) colonization, attachment, development, dispersal
3. C) development, colonization, attachment, dispersal
4. D) attachment, development, colonization, dispersal
14) Pseudomonas aeruginosa is a(n) pathogen. 1. A) opportunistic 2. B) idiopathic 3. C) pessimistic 4. D) iatrogenic
15) Which of the following activities is a result of cyclic di-guanosine monophosphate synthesis?
1. A) transition from planktonic to sessile growth during biofilm formation
2. B) reduction in activity of flagellar motor
3. C) biosynthesis of extracellular matrix during biofilm formation
4. D) All of these answer choices activities are a result of cyclic di- guanosine
monophosphate synthesis.
16) The major symptoms of the genetic disorder cystic fibrosis are caused due to biofilm formation by
1. A) Serratia marcesans.
2. B) Pseudomonas aeruginosa.
3. C) Vibrio cholera.
4. D) Bacillus subtilis.
17) All of the following are targets of currently used antibiotics EXCEPT 1. A) DNA synthesis.
2. B) biofilm formation. 3. C) transcription. 4. D) translation.
18) When a Bacillus anthracis population suddenly must form spores to survive a harsh
nutrient poor environment, how do the cells obtain energy?
1. A) Cells in a growth phase that have not used up all of their energy will be the only ones
to make endospores, which is why relatively few endospores are often made from a large population.
2. B) Intracellular energy reserves are quickly made available to produce endospores.
3. C) Slow responding cells are cannibalized by others that already began spore formation.
4. D) Global regulation is initiated to minimize energy waste in biosynthetic pathways and
catabolic pathways are increased to consume remaining usable substrates to fuel spore formation.
19) Bacteria from the genus Caulobacter are used to model cellular differentiation in
eukaryotes. The abundance of CtrA, DnaA, and GcrA separately control activity of other
genes necessary for differentiation in Caulobacter. Thus, these three proteins can be classified as 1. A) activating sensors.
2. B) heterologous regulators.
3. C) differentiating regulons.
4. D) transcriptional regulators.
20) A bacterium that either partially or fully catabolizes an acyl-homoserine lactone will likely disrupt 1. A) attenuation. 2. B) chemotaxis. 3. C) endospore formation. 4. D) quorum sensing.
21) Quorum sensing generally follows the mechanism of which type of regulation? 1. A) feedback inhibition
2. B) negative transcriptional regulation
3. C) positive transcriptional regulation
4. D) a two-component regulation system 22) Penicillins work by
1. A) activating autolytic enzymes.
2. B) blocking the transpeptidation reaction that forms peptidoglycan cross-links.
3. C) stimulating autolysins to form holes in the plasma membrane.
4. D) All of these answer choices are true. 23) σF functions as a(n) during endospore formation.
1. A) transcription factor 2. B) anti-sigma factor 3. C) protease 4. D) RNase
24) When Spo0A is highly phosphorylated
1. A) heterocyst formation is initiated.
2. B) stalk formation is initiated.
3. C) endospore formation is initiated.
4. D) photosynthesis is initiated.
25) What is the function of heterocysts in cyanobacteria such as Anabaena?
1. A) nitrogen fixation 2. B) sexual reproduction 3. C) asexual reproduction 4. D) photosynthesis
26) The major shape-determining factor in Bacteria is the protein 1. A) FtsZ. 2. B) crescentin. 3. C) MreB. 4. D) MinD.
27) In the process of binary fission in Bacteria, which action occurs first?
1. A) formation of the divisome 2. B) DNA replication 3. C) cell elongation 4. D) cytokinesis 28) FtsZ is related to
, an important protein involved in cell division. 1. A) actin 2. B) myosin 3. C) tubulin 4. D) collagen 29) FtsA is related to
, an important cytoskeletal protein in eukaryotes. 1. A) actin 2. B) myosin 3. C) tubulin 4. D) collagen
30) Endospore formation is stimulated when
1. A) bacterial growth ceases due to limitation of an essential nutrient.
2. B) the bacterium is undergoing binary fission.
3. C) bacteria are dividing exponentially. 4. D) nutrient levels rise.
31) Proteins MinC, MinD, and MinE interact to 1. A) help guide FtsZ to the cell midpoint.
2. B) initiate peptidoglycan synthesis.
3. C) assist chromosome segregation. 4. D) determine cell shape.
32) The curved-rod shape typical of Caulobacter is due to the protein(s) 1. A) crescentin. 2. B) MreB.
3. C) crescentin and MreB.
4. D) neither crescentin nor MreB.
33) Which of the following traits is NOT characteristic of the Caulobacter life cycle?
1. A) Cell division only occurs in the swarmer stage.
2. B) Cell division only occurs in the stalked cell stage.
3. C) Chromosome replication only occurs in the swarmer stage.
4. D) Chromosome replication and cell division only occurs in the stalked cell stage.
34) Biofilm formation in Pseudomonas aeruginosa is triggered by cell densities and repressed by cell densities. 1. A) high; high 2. B) low; low 3. C) high; low 4. D) low; high
35) Biofilm formation in Vibrio cholera is triggered by and cell densities repressed by cell densities. 1. A) high; high 2. B) low; low 3. C) high; low 4. D) low; high
36) What is the function of bactoprenol?
1. A) It is a hydrophobic alcohol that transports peptidoglycan precursors across the cytoplasmic membrane.
2. B) It is responsible for forming the peptide cross-links between muramic acid residues in adjacent glycan chains.
3. C) It triggers the recruitment of FtsZ and the initiation of the divisome.
4. D) It supplies the energy necessary for transpeptidation to occur.
37) Shortage of key nutrients such as results in transcription and
secretion of a toxic protein that leads to cannibalization of neighboring cells of the same species. 1. A) magnesium 2. B) phosphate 3. C) calcium
38) Heterocysts are specialized cells that undergo
1. A) oxidative phosphorylation. 2. B) photophosphorylation.
3. C) nitrogen fixation. 4. D) lysine decarboxylation
39) Which of the following is NOT a function of DnaA in Caulobacter?
1. A) initiation of DNA replication
2. B) initiation of swarming
3. C) transcriptional regulation
4. D) All of these answer choices are functions of DnaA.
40) Why is the presence of a cell wall significant from a clinical standpoint?
1. A) All types of cells have a cell wall, and it makes identification of the causative agent of disease difficult.
2. B) The cell wall protects microorganisms from destruction by the immune system.
3. C) Animal cells do not have cell walls, so antibiotics that target cell walls can
selectively destroy invading microorganisms.
41) D) Only gram-negative Bacteria have Which of the following molecules functions as an
intracellular signaling molecule during quorum sensing?
1. A) acylated homoserine lactones 2. B) hydrophilic lipids 3. C) quinones 4. D) proteorhodopsins
42) Dormancy is a result of all of the following EXCEPT
1. A) phenotypic heterogeneity.
2. B) ineffective efflux pumps. 3. C) TA modules. 4. D) the stringent response. 7.2 True/False Questions
1) The purpose of hemimethylated DNA is to block chromosome replication. Answer: TRUE
2) Plasmids are replicated in Escherichia coli using the Par system. Answer: FALSE
3) PopZ plays a critical role in localizing proteins to the cell poles. Answer: TRUE
4) The Par system is analogous to spindle fibers in eukaryotic cells. Answer: TRUE
5) In the Caulobacter life cycle, the role of swarmer cells is strictly for reproduction. Answer: FALSE
6) Biofilm formation is more likely to occur when Vibrio cholerae is found in low densities such as sea water. Answer: TRUE
7) Multiple sigma factors are essential to induce the biosynthesis of endospores, consequently
a complex regulatory mechanism such as this has a higher chance of mutation leading to
incorrect functioning compared to a simple repression mechanism. Answer: TRUE
8) Generation of new bacillus-shaped cells starts with one cell elongating and terminates when
it splits into two separate bacilli. Answer: TRUE
9) The activity of MinC and MinD direct whether a bacterial cell will be coccoid or bacillus shaped. Answer: FALSE
10) In fast-growing Escherichia coli cells, multiple replication forks of genomic DNA allows
binary fission to occur before the genome has been fully duplicated. Answer: FALSE
11) Multiple sigma factors are essential to induce the formation of endospores. Answer: TRUE
12) During elongation of a cell during binary fission, small gaps caused by transglycosylases
are formed before cell membrane precursors can be inserted. Answer: FALSE
13) Antibiotic resistance can develop in a bacterium as a result of spontaneous mutation. Answer: TRUE
14) Natural antibiotics are produced by all bacterial genera. Answer: FALSE
15) All members of the genus Pseudomonas respond similarly to c-di-GMP. Answer: FALSE
16) The spherical shape of Staphylococcus aureus is a result of MreB function. Answer: FALSE
17) Both crescentin and MreB play a role in formation of the vibrio-shaped bacterium Caulobacter. Answer: TRUE
18) FtsZ is analogous to the protein tubulin in eukaryotic cells. Answer: FALSE
19) In both cocci as well as rod-shaped cells, new peptidoglycan synthesis occurs in both
directions from the central location of the FtsZ ring. Answer: FALSE
20) Oxygenic phototrophs require the uptake of oxygen for the reactions of photosynthesis. Answer: FALSE
21) Mobile resistance genes encode enzymes that inactivate an antibiotic by altering its structure. Answer: TRUE
22) Unlike penicillin, methicillin targets an alternative penicillin binding protein called MecA
in nonresistant Staphylococcus aureus. Answer: FALSE
23) MRSA strains synthesize MecA only in the presence of methicillin or other β-lactam antibiotics. Answer: TRUE
24) Antibiotic-sensitive bacteria sometimes produce cells that are transiently resistant to multiple antibiotics. Answer: TRUE
25) When Mycobacterium tuberculosis is in the dormant state it is still susceptible to
antibiotics, but the rate of death is slower. Answer: FALSE
26) Persistence is a heritable trait. Answer: FALSE
27) The toxin component of TA modules helps ensure survival during stressful growth conditions. Answer: TRUE
28) Free HipA toxin inhibits transcription. Answer: FALSE 7.3 Essay Questions
1) Describe the functions of the FtsZ protein and the Z-ring in bacterial cells.
Answer: FtsZ is an essential cell division protein that forms a contractile ring structure (Z ring)
at the future cell division site. The regulation of the ring assembly controls the timing and the
location of cell division. One of the functions of the FtsZ ring is to recruit other cell division
proteins to the septum to produce a new cell wall between the dividing cells.
2) What is the purpose of the MreB protein in bacteria?
Answer: The bacterial actin homologue MreB is required for the maintenance of a rod-shaped
cell and has been shown to form spirals that traverse along the longitudinal axis of Bacillus
subtilis and Escherichia coli cells.
3) What role does the Par system play in bacterial cell division?
Answer: The Par (partitioning) system can be found in many bacteria including Caulobacter
which undergoes budding. Similar to mitotic spindle fibers which separate replicated
chromosomes in eukaryotic cells, the Par system distributes chromosomes and plasmids equally
to progeny cells during growth. This system is composed of the ParAATPase, the ParB
chromosome- binding protein, and the PopZ complex, as well as a centromere-like parS
sequence located near oriC.
4) A researcher unexpectedly identified mutant bacteria deficient in the FtsZ protein. Their
growth appeared filamentous, and displayed incomplete cell division. Explain the role of
the FtsZ protein and how a deficiency would account for this altered growth.
Answer: FtsZ is an essential cell division protein that forms a contractile ring structure (Z ring)
at the future cell division site. The regulation of the ring assembly controls the timing and the
location of cell division. One of the functions of the FtsZ ring is to recruit other cell division
proteins to the septum to produce a new cell wall between the dividing cells. Consequently, a
mutation in this protein would result in incomplete cell division and a potentially filamentous appearance.
5) How might a genetically modified strain of E.coli with a nonfunctional mreB gene
compare to E. coli possessing a functional mreB gene?
Answer: MreB forms a simple cytoskeleton in Bacteria by forming patchlike filaments around
the inside of the cell just below the cytoplasmic membrane. The MreB cytoskeleton is thought to
define cell shape by recruiting other proteins that function in cell wall growth to group in a specific pattern.
Inactivation of the gene encoding MreB in rod-shaped bacteria causes the cells to become coccus-shaped.
6) Explain how FtsZ-type proteins being found in mitochondria and chloroplasts strengthens
or weakens the endosymbiosis theory.
Answer: The protein FtsZ, encoded by the gene ftsZ, is specifically involved in prokaryotic cell
division. FtsZ-like proteins identified in mitochondria and chloroplasts suggest the
FtsZencoding gene was first present in prokaryotes and that these two organelles were
subsequently developed and maintained in Eukarya. Ultimately this corroborates the ideas of the
endosymbiotic theory and seemingly links chloroplast and mitochondrial origins to prokaryotes.
7) Explain the role of CtrA in the formation of swarmer cells in Caulobacter.
Answer: CtrA is activated by phosphorylation in emerging swarmer cells in response to external
signals. Once phosphorylated, CtrA-P activates genes that encode synthesis of the flagellum and
other functions specific to swarmer cells. Conversely, CtrA-P represses the synthesis of the
protein CcrA and so inhibits the initiation of DNA replication in swarmer cells by binding to and
blocking the origin of replication.
8) Explain how green fluorescent protein (GFP) could be utilized to determine the role of
FtsZ in binary fission in Escherichia coli.
Answer: For visualizing molecular events, reporter genes that encode fluorescent products such
as green fluorescent protein (GFP) are routinely used. In this case, the gene for the production of
GFP would be incorporated into the genome of Escherichia coli in the region of the DNA that
codes for the FtsZ gene so that both genes are controlled by the same regulatory sequence; that
is, the gene’s regulatory sequence now controls the production of GFP, in addition to FtsZ. In
cells where the gene is expressed, and the tagged FtsZ proteins are produced, GFP is produced
at the same time. Thus, only those cells in which the tagged gene is expressed, or the target
proteins are produced, will fluoresce when observed under fluorescence microscopy.
9) Explain the impact spontaneous mutation of the gene minE in an Escherichia coli
bacterium would have on future cell divisions.
Answer: The MinE protein is one of three proteins of the Min system encoded by the minB
operon required to generate pole to pole oscillations prior to bacterial cell division as a means of
specifying the midzone of the cell. If a spontaneous mutation were to occur resulting in
inactivation of this protein, it would affect cell division in the next generation since the FtsZ
ring would not form and cell division would not occur.
10) Compare the process of new peptidoglycan formation in cocci versus rod- shaped cells.
Answer: In cocci, new cell wall material grows out in opposite directions from the FtsZ
ring. In contrast, new cell wall grows at several locations along the length of a rod-shaped cell.
11) The chemical composition of the peptidoglycan carrier bactoprenol is highly hydrophobic.
Explain why this is necessary for bactroprenol to carry on its function.
Answer: Bactoprenol is a hydrophobic C55 alcohol that bonds to peptidoglycan precursors.
Bactoprenol transports peptidoglycan precursors across the cytoplasmic membrane by rendering
them sufficiently hydrophobic to pass through the fatty acid tails of the membrane interior. Once
in the periplasm, bactoprenol interacts with enzymes called transglycosylases that insert cell
wall precursors into the growing point of the cell wall and catalyze glycosidic bond formation.
12) How does the antibiotic penicillin lead to the death of pathogens?
Answer: Several penicillin binding proteins have been identified in bacteria, including FtsI.
When penicillin is bound to penicillin-binding proteins, the proteins lose their catalytic activity.
In the absence of transpeptidation, the continued activity of autolysins so weakens the cell wall
that the cell eventually bursts.
13) Describe the steps of binary fission.
Answer: 1) Replication of the circular prokaryotic chromosome begins at the origin of replication
and continues in both directions at once. 2) The cell begins to elongate. FtsZ proteins migrate
toward the midpoint of the cell. 3) The duplicated chromosomes separate and continue to move
away from each other toward opposite ends of the cell. FtsZ proteins form a ring around the
periphery of the midpoint between the chromosomes. 4) The FtsZ ring directs the formation of a
septum that divides the cell. Plasma membrane and cell wall materials accumulate. 5) After the
septum is complete, the cell pinches in two, forming two daughter cells. FtsZ is dispersed
throughout the cytoplasm of the new cells.
14) Explain why the antibiotic penicillin is effective at destroying bacteria but does not have a
similar effect in eukaryotic cells.
Answer: Animal cells do not possess a cell wall and therefore lack peptidoglycan. Consequently
the drug can be administered in high doses and is typically nontoxic. Most pathogenic bacteria
do have cell walls composed of peptidoglycan and are thus potential targets of the drug.
15) The major trigger of endospore formation in Bacillus is nutrient deprivation. Without the
appropriate nutrients, how can endospore formation occur?