Chapter 7 - Microbial Growth

At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has a population of 65 million cells. The mean generation time is approximately A. 10 minutes. B. 20 minutes. C. 30 minutes. D. 40 minutes.

20 minutes.

Given a log phase bacterial culture with 1 x 106 cells per ml and a generation time of 30 minutes, how long does it take the culture to reach a density of 6.4 107 cells per ml? A. 1 hour B. 2 hours C. 3 hours D. 4 hours

3 hours

The length of the lag phase of growth can vary depending on A. the condition of the microorganisms. B. the nature of the growth medium. C. the temperature. D. All of the choices are correct.

All of the choices are correct.

Which of the following can be used to isolate pure cultures of bacteria from mixtures? A. Spread plates B. Streak plates C. Pour plates D. All of the choices are correct.

All of the choices are correct.

Which of the following may form one colony? A. A single bacterial cell B. A short chain of bacteria C. A small clump of bacteria D. All of the choices are correct.

All of the choices are correct.

Which of the following strategies enable non-acidophilic bacteria to endure lower pH environments? A. Presence of internal buffers B. Proton pumps that pump H+ out of the cell C. Synthesis of acid shock proteins that protect other cellular proteins D. All of the choices are correct.

All of the choices are correct.

Which of the following do airborne microorganisms and microorganisms on light-exposed surfaces use to protect themselves from photooxidation? A. Catalase enzymes B. Peroxidase enzymes C. Carotenoid pigments D. Superoxide dismutase

Carotenoid pigments

All fastidious microorganisms require which of the following for growth? A. Oxygen B. Temperatures near normal for the human body C. Extra nutrients (such as whole blood) D. Iron

Extra nutrients (such as whole blood)

Most microorganisms live in eutrophic environments. (T/F)

False

The process of segregating the daughter chromosomes in Sulfolobus is more similar to the process in eukaryotic cells than in bacterial cells. (T/F)

False

The purpose of the penicillin binding proteins is to link phospholipids together in the cellular membrane. (T/F)

False

Which of these methods can be used to determine the number of viable microorganisms in a sample? A. Light scattering in a spectrophotometer B. Measuring total cell mass C. Measuring colony forming units per ml D. Counting a known volume of cells in a hemocytometer

Measuring colony forming units per ml

A microbiologist is testing the drinking water for a municipality. What would be the best method for testing the purified water? A. Viable plate count B. Measurement of microbial mass C. Direct microscopic count D. Membrane filtration

Membrane filtration

The actin-like protein that seems to be involved in determining cell shape is A. MreB. B. ActA. C. SpnC. D. FtsZ.

MreB.

Which of the following methods could be used to detect the presence of viable but nonculturable cells of a pathogen in a water or food specimen? A. Culture on enriched agar B. Use of enrichment techniques C. Polymerase chain reaction D. Culture on selective agar

Polymerase chain reaction

How is budding of bacteria to produce daughter cells different from binary fission? A. The chromosome does not need to be replicated. B. The cytoplasmic division is unequal. C. The bud doesn't receive any DNA. D. A septum must form during budding.

The cytoplasmic division is unequal.

The growth rate of a given species of microorganism is dependent on the composition of the medium in which it is grown. (T/F)

True

Organisms that grow in the mud under relatively nonturbulent bodies of water are likely to be A. obligate aerobes. B. thermophilic. C. barophilic. D. anaerobes.

anaerobes.

Macroscopically visible growths or clusters of microorganisms on solid media are called __________.

colonies

When counting colonies during viable cell counts, the results are expressed as ________ ________ _______ because it is impossible to determine that each colony arose from a single cell.

colony forming units

Media containing some ingredients of unknown chemical composition are called __________ media. A. undefined B. complex C. defined D. synthetic

complex

A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system. A. continuous B. batch C. fed-batch D. semicontinuous

continuous

A growth medium that distinguishes among different groups of bacteria on the basis of their biological characteristics is called a __________ medium. A. selective B. differential C. enrichment D. transport

differential

In a continuous culture system, the rate at which media is added and removed is called the __________ rate. A. dilution B. chemostatic C. pass-through D. flow-through

dilution

Colonies grow most rapidly at the __________ where oxygen and nutrients are readily available; however, they grow less rapidly at the __________ where these materials have been depleted.

edge, center

A culture technique that encourages the growth of specific microbes while inhibiting the growth of others is a(n) __________ culture.

enrichment

Microorganisms are most nearly uniform in terms of chemical and physiological properties during __________ phase. A. lag B. exponential C. stationary D. decline

exponential

Bacteria reproductive strategies include all of the following EXCEPT A. binary fission. B. budding. C. multiple fission. D. formation of mutinucleoid filaments that break apart into uninucleate spores. E. fusion of two bacterial cells that then split into four uninucleate cells.

fusion of two bacterial cells that then split into four uninucleate cells.

Organisms that require high levels of sodium chloride in order to grow are called __________ organisms.

halophilic

Organisms that are damaged by the normal atmospheric levels of oxygen (20%) but require oxygen at levels of 2-10% for growth are called A. facultative anaerobes. B. microaerophiles. C. aerotolerant. D. anoxygenic.

microaerophiles.

Organisms that have their optimum growth pH between 5.5 and 8.0 are called __________.

neutrophiles

Quorum sensing in Gram-positive bacteria generally involves the use of ____________ as the external signaling molecules.

oligopeptides

Organisms that grow well at 0C and have optimum growth temperatures of 15C or lower are called A. psychrotrophs. B. psychrophiles. C. frigiphiles. D. mesophiles.

psychrophiles.

The __________ is a group of proteins needed for DNA synthesis that assembles at the origin of replication. A. septum B. replisome C. prospore D. None of the choices are correct.

replisome

A growth medium that favors the growth of some microorganisms but inhibits the growth of other microorganisms is a __________ medium. A. selective B. differential C. selective and differential D. neither selective nor differential

selective

The limitation on microbial growth rate at high nutrient levels is/are A. the rate of protein synthesis. B. the rate of DNA replication. C. the saturation of the transport proteins for nutrient uptake. D. All of the choices are correct.

the saturation of the transport proteins for nutrient uptake

Organisms that grow near deep-sea volcanic vents are likely to be A. psychrophilic. B. psychrotrophic. C. mesophilic. D. thermophilic.

thermophilic.

One hypothesis about the decline in cell numbers during death phase is that the cells aren't all dying but instead remain alive but unable to grow when cultured, at least temporarily. These are known as A. viable but nonculturable cells. B. ghost cells. C. death phase cells. D. programmed death cells.

viable but nonculturable cells.

Place the steps of biofilm formation in the correct order.

1 Surface (substratum) is preconditioned by environmental molecules. 3 Quorum sensing and the establishment of the extracellular matrix commences as microbes attach more stably. 4 Biofilm matures and some microorganisms escape to the planktonic state. 2 Microbes attach and detach from the preconditioned surface.

At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the log phase culture has population of 65 million cells. The approximate number of generations that has occurred is A. 5. B. 13. C. 21. D. 27.

13

Which of the following can be used to estimate the number of microorganisms in a culture? A. Direct counts of microbial cells B. Counts of viable cells using colony growth procedures C. Measurements of microbial biomass D. All of the choices are correct.

All of the choices are correct.

Which of the following is considered a cardinal growth temperature? A. The minimum temperature B. The maximum temperature C. The optimum temperature D. All of these are considered cardinal growth temperatures.

All of these are considered cardinal growth temperatures.

Organisms that have their optimum growth pH between 0.0 and 5.5 are called __________.

acidophiles

Organisms that ignore oxygen and grow equally well in its presence or absence are called A. facultative anaerobes. B. microaerophiles. C. aerotolerant. D. anoxygenic.

aerotolerant.

For surface cultivation of microorganisms, a sulfated polymer called agar can be extracted from __________ and added to liquid media in order to cause it to solidify. A. bacteria B. animal fat C. algae D. fungi

algae

Organisms that have their optimum growth pH between 8.5 and 11.5 are called __________.

alkaliphiles

Organisms that grow near deep-sea volcanic vents are likely to be A. alkylophilic. B. acidophilic. C. barophilic or barotolerant. D. picrophilic.

barophilic or barotolerant.

Organisms that require increased pressure for optimum growth are called A. barotolerant. B. osmotolerant. C. barophilic. D. osmophilic.

barophilic.

Organisms that are not drastically affected by increased pressure are called A. barotolerant. B. osmotolerant. C. barophilic. D. osmophilic.

barotolerant.

Most bacterial and archaeal cells divide by A. mitosis. B. meiosis. C. binary fission. D. All of the choices are correct.

binary fission.

An open system in which the growth rate is maintained by adding a nutrient (present in limiting quantities) at the same rate that medium containing microorganisms is removed is called a A. manostat. B. chemostat. C. turbidostat. D. culturostat.

chemostat.

Media in which all components and their concentration are known are called __________ media. A. transport B. defined C. selective D. enrichment

defined

Mannitol salt agar (MSA) only allows the growth of halophiles (salt-loving microbes); nonhalophiles will not grow. Among the halophiles, mannitol fermenters will produce acid that turns the pH indicator yellow; mannitol nonfermenters leave the medium red. Onto MSA you inoculate a halophilic mannitol fermenter and a halophilic mannitol nonfermenter. In this case, the medium is acting as (a) __________ medium(s). A. selective B. differential C. selective and differential D. enrichment

differential

Organisms that grow at 0C and have a maximum growth temperature of 35C are called A. psychrotrophs. B. psychrophiles. C. frigiphiles. D. mesophiles.

psychrotrophs

Mannitol salt agar (MSA) only allows the growth of halophiles (salt-loving microbes). Among the halophiles, mannitol fermenters release acid that turns the pH indicator yellow; mannitol nonfermenters leave the medium red. Onto MSA you inoculate a halophilic mannitol nonfermenter and a nonhalophilic mannitol nonfermenter. Here the medium acts as a __________ medium. A. selective B. differential C. selective and differential D. enrichment

selective

All of the following are characteristics of spread plates EXCEPT A. colonies that grow on the surface of the agar. B. specimens that are typically diluted prior to inoculation of a spread plate. C. spread plates that readily grow anaerobic bacteria. D. spread plates that are typically inoculated with a bent glass rod.

spread plates that readily grow anaerobic bacteria

An open system in which the growth rate is maintained by the removal and addition of media at such a rate as to maintain a constant cell density is called a A. manostat. B. chemostat. C. turbidostat. D. culturostat.

turbidostat.

The cell wall of bacteria constrains the ___________ _________ that results from the osmolarity of the cytoplasmic contents.

turgor pressure

The membranes of psychrophilic bacteria have relatively high levels of __________ fatty acids, which allow them to remain semifluid at cold temperatures. A. saturated B. unsaturated C. sterol D. aromatic

unsaturated

You would like to culture a bacterium that is growing in the lung of a human patient with pneumonia. Which media would be of most use in culturing this organism? A. Transport media B. Mannitol salt agar C. MacConkey's agar D. Complex medium supplemented with whole blood E. None of the choices are correct.

Complex medium supplemented with whole blood

A given medium can be either selective or differential but not both. (T/F)

False

A microbial environment containing high nutrient concentrations is called an oligotrophic environment. (T/F)

False

All bacterial and archaeal cells are diploid. (T/F)

False

During the lag phase of microbial growth, the cells are metabolically inactive. (T/F)

False

Serial dilutions can be used to estimate the total number of bacterial cells in a solution, including living and dead cells. (T/F)

False

The size and shape of a colony is not useful for identification of a microorganism because most microorganisms produce colonies that are indistinguishable from one another. (T/F)

False

There doesn't appear to be much diversity in the cell cycle processes of the Archaea, and Sulfolobus serves as an excellent model for all other Archaea. (T/F)

False

When a young, vigorously growing culture of bacteria is transferred to fresh medium of different composition, the lag phase is usually short or absent. (T/F)

False

Unlike Sulfolobus, some Archaea use ___________ protein(s) to accomplish cytokinesis. A. Tubulin B. Seg A and Seg B C. CdvA, CdvB, and CdvC D. FtsZ

FtsZ

Which type of lifestyle is demonstrated by bacteria in biofilms? A. Planktonic B. Photoautotrophic C. Parasitic D. Sessile

Sessile

What is the result of successful communication between rhizobia and their plant hosts? A. Rhizobia consume the plant tissue as an energy and carbon source, causing disease in the plant. B. The plant consumes rhizobiaas an energy source and carbon, destroying the invading bacteria. C. The rhizobia invade the plant root and begin to fix nitrogen with the assistance of the plant. D. The plant supplies organic forms of nitrogen to the rhizobia.

The rhizobia invade the plant root and begin to fix nitrogen with the assistance of the plant.

Which of the following is most similar between the cell cycle process of Sulfolobus and that of bacteria? A. The segregation of the chromosomes B. The cytokinesis process C. The timing of events during G1, S, and G2

The segregation of the chromosomes

Membranes of some thermophilic Archaea are stabilized by ether linked phospholipids. (T/F)

True

Obligate anaerobes are usually poisoned by molecular oxygen but may grow in aerobic habitats if associated with facultative anaerobes that use up all available oxygen. (T/F)

True

One of the major advantages of a continuous culture system is that the cells can be maintained in the exponential growth phase for extended periods of time. (T/F)

True

When a young, vigorously growing culture of bacteria is transferred to fresh medium of the same composition, the lag phase is usually short or absent. (T/F)

True

While establishing a symbiotic relationship, plant hosts communicate with bacteria via secretion of flavonoids and bacteria release Nod factors to communicate with the plant. (T/F)

True

A microbiologist is studying the growth of a particular strain of bacteria to determine when it will transition from exponential growth to stationary phase and from stationary phase to death phase. Which of the following methods of measuring microbial growth would be best for this purpose? A. Direct microscopic count B. Determining dry weight of microbes C. Turbidimetric measurements using a spectrophotometer D. Viable plate count

Viable plate count

At 4:00 p.m. a closed flask of sterile broth is inoculated with 10,000 cells. The lag phase lasts 1 hour. At 9:00 p.m. the culture enters stationary phase with a population of 65 million cells. At what time is the population half maximal? A. 6:30 p.m. B. 7:20 p.m. C. 8:20 p.m. D. 8:40 p.m.

8:40 p.m.

Cells may enter stationary phase because of A. the depletion of an essential nutrient. B. a lack of available oxygen. C. the accumulation of toxic waste products. D. All of the choices are correct.

All of the choices are correct.

Quorum sensing A. is a phenomenon in which bacteria monitor their own population density. B. depends on the sensing of signal protein molecules. C. plays an important role in formation of biofilms by Pseudomonas aeruginosa. D. All of the choices are correct.

All of the choices are correct.

Which of the following are a reason(s) for the decline in cell numbers during the death phase? A. Depletion of nutrients B. Accumulation of toxic waste materials C. Depletion of O2 D. All of the choices are correct.

All of the choices are correct.

Which of the following is a reason for the occurrence of a lag phase in a bacterial growth curve? A. The cells may be old and depleted of ATP, essential cofactors, and ribosomes that must be synthesized before growth can begin. B. The medium may be different from the previous growth medium so that the cells must synthesize new enzymes to use different nutrients. C. The organisms may have been injured and require time to recover. D. All of these are potential reasons.

All of these are potential reasons.

Which of the following proteins is central to starvation survival strategies in many bacteria? A. Fts Z B. RpoS C. Superoxide dismutase D. ATPase

RpoS

A culture in a closed vessel to which no additional medium is added and from which no waste products are removed is called a __________ culture. A. continuous B. batch C. fed-batch D. semicontinuous

batch

Complex microbial communities that grow tightly adhered to surfaces are called __________.

biofilms

The __________ __________ is the length of time it takes for a population of microorganisms to double in number.

generation time

Microbial __________ is an increase in cell constituents that may or may not be accompanied by an increase in cell number.

growth

Mannitol salt agar (MSA) only allows the growth of halophiles (salt-loving microbes). Among the halophiles, mannitol fermenters release acid that turns the pH indicator yellow; mannitol nonfermenters leave the medium red. Onto MSA you inoculate a halophilic mannitol fermenter, a nonhalophilic mannitol fermenter, and a halophilic mannitol nonfermenter. Thus, the medium is acting as a __________ medium. A. selective B. differential C. selective and differential D. neither selective nor differential

selective and differential

The process of forming a cross wall between two daughter cells is known as _______________. A. replication B. septation C. sporulation D. mitosis

septation

Bacteria that live attached to surfaces are described as ___________, whereas bacteria that are free-living, floating with a fluid environment are described as _________.

sessile; planktonic

A microbiologist is trying to isolate a pathogen expected to be present in very small numbers from a stool specimen in which there are abundant normal microbiota. Which strategy would most likely accomplish this purpose? A. Culture on enriched media B. Enrichment culture followed by culture on selective agar C. Culture on differential media D. Culture in an anaerobe jar

Enrichment culture followed by culture on selective agar

Which of the following is the correct order for binary fission? A. A septum forms at midcell, the cell elongates, replicates its chromosome, and separates the chromosome into the two parts of the cell. B. The cell elongates, a septum forms at midcell, the cell replicates its chromosome, and separates the chromosome into the two parts of the cell. C. The cell elongates, replicates its chromosome, and separates the chromosome into the two parts of the cell, and a septum forms at midcell. D. None of the choices are correct.

The cell elongates, replicates its chromosome, and separates the chromosome into the two parts of the cell, and a septum forms at midcell.

How is the cell cycle of Sulfolobus spp. similar to that of eukaryotes? A. Sulfolobus has microtubules composed of a tubulin homolog that separate the chromosomes. B. Sulfolobus demonstrates prophase, metaphase, anaphase, and telophase. C. A centrosome is apparent in Sulfolobus during G2. D. The cytokinesis process in Sulfolobus is similar to the process in eukaryotes.

The cytokinesis process in Sulfolobus is similar to the process in eukaryotes.

A microbiologist is attempting to determine the size of a microbial population and has employed several methods. She noticed that the direct count she obtained using a counting chamber and microscope was much higher than her estimate from doing a viable plate count. This discrepancy was encountered during multiple trials. What is the most likely reason for the discrepancy? A. She counted incorrectly. B. She did not correctly do the serial dilutions prior to the viable plate count. C. Many of the organisms viewed during the direct count may be dead. D. The medium and growth conditions used for the viable count will not support the growth of the organisms. E. The organisms were not readily cultured on the viable count, either because many were dead or because the medium and growth conditions used for the viable count will not support the growth of the microorganism.

The organisms were not readily cultured on the viable count, either because many were dead or because the medium and growth conditions used for the viable count will not support the growth of the microorganism.

The total number of viable microorganisms remains constant in stationary phase because A. there is a balance between cell division and cell death. B. there is a cessation of cell division even though the cells may remain metabolically active. C. either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active. D. None of the choices are correct.

either there is a balance between cell division and cell death or there is a cessation of cell division even though the cells may remain metabolically active.

Organisms that grow best at pH levels above 10 are called __________ __________.

extreme alkaliphiles

Organisms that do not require oxygen for growth but grow better in its presence are called A. facultative anaerobes. B. microaerophiles. C. aerotolerant. D. anoxygenic.

facultative anaerobes.

Membranes of thermophilic bacteria are stabilized by phospholipids with A. fatty acids that tend to be more saturated. B. fatty acids that have lower molecular weights. C. fatty acids that have more double bonds. D. All of the choices are correct.

fatty acids that tend to be more saturated.

Growth media that will support the growth of many different types of microorganisms are called __________ __________ growth media, whereas those that are supplemented by blood or other rich nutrient sources in order to support the growth of fastidious organisms are called __________ media.

general purpose, enriched

Agar is an excellent solidifying agent for microbiological media because A. it is not degraded by most microorganisms. B. solid agar remains solid until the temperature is raised to 90C, and liquid agar remains liquid if the temperature is lowered to 45C. C. it is not degraded by most microorganisms and solid agar remains solid until the temperature is raised to 90C, and liquid agar remains liquid if the temperature is lowered to 45C are correct. D. agar provides an excellent source of nutrition for a variety of different microorganisms.

it is not degraded by most microorganisms and solid agar remains solid until the temperature is raised to 90C, and liquid agar remains liquid if the temperature is lowered to 45C are correct.

Most microorganisms maintain their internal pH A. near neutral (pH 7). B. near their optimum growth pH. C. slightly acidic (pH 4-6). D. slightly alkaline (pH 8-10).

near neutral (pH 7).

The site at which replication of DNA starts in bacterial cells is known as the __________ of ___________.

origin, replication

Organisms that can grow in habitats with low water activity by maintaining a high internal salt concentration are called __________ organisms.

osmotolerant

A common type of autoinducer found in gram-negative bacteria are acyl homoserine lactones (AHL). (T/F)

True

All of the colonies form on the surface of a spread plate, whereas on a pour plate, colonies may be embedded in the agar as well as on the surface. (T/F)

True

Blood agar is both a differential and enriched medium. (T/F)

True

DNA of thermophiles is stabilized by binding of special nucleoid-associated proteins. (T/F)

True

During the cell division process, Sulfolobus segregates its chromosomes in a manner similar to bacteria, and performs cytokinesis in a manner similar to that of eukaryotes. (T/F)

True

Which of the following might be missed if viable counts are done on food and/or water specimens? A. Endospores B. Aerobic bacteria C. Viable but nonculturable cells D. Pathogenic bacteria

Viable but nonculturable cells

During cytokinesis, a critical step in septation is the assembly of the A. replisome. B. spindle body. C. Z ring. D. cytoskeletal spiral.

Z ring.