Chapter 4

The human intestinal tract has been likened to a culture vessel. The most commonly used lab culture systems include batch culture (growth in a test tube or flask) and chemostats. Sort the following list of features into the appropriate categories depending on whether they are characteristic of a batch culture, the gut tract, a chemostat, or gut and chemostat. OPTIONS: Mixed species Continuous nutrient input One-time supply of nutrients Bacterial numbers remain relatively constant Sporadic nutrient input Continuous removal of cells and fluid Defined death phase Nutrients entering are balanced by wastes exiting Fluid absorbed during culture Cells do not exit Bacterial numbers change throughout CATEGORIES: Gut Tract Chemostat Batch Culture Gut & Chemostat

#1) Gut Tract: Mixed species Sporadic nutrient input Fluid absorbed during culture #2) Chemostat: Continuous nutrient input Continuous removal of cells and fluid #3) Batch Culture: One-time supply of nutrients Defined death phase Cells do not exit Bacterial numbers change throughout #4) Gut & Chemostat: Bacterial numbers remain relatively constant Nutrients entering are balanced by wastes exiting

1) Which organisms produce alginate, the substrate for the AguEFG transporter system of the marine microbe Thermotoga maritima? A. brown seaweeds B. land plants C. E. coli D. Pseudomonas aeruginosa 2) How can purified siderophores from one bacterium be used to inhibit the growth of another bacterium? A. The siderophores from one bacterium can absorb free iron in the media or surrounding environment, thereby depriving the second bacterium of the needed nutrient. B. The siderophores from one bacterium can transport too much iron into the second bacterium, causing toxic side effects. C. The siderophore from one bacterium can be toxic to the second bacterium. D. The siderophores from one bacterium can overwhelm and inhibit the ABC transporters of the second bacterium.

#1. A. brown seaweeds #2. A. The siderophores from one bacterium can absorb free iron in the media or surrounding environment, thereby depriving the second bacterium of the needed nutrient.

1) The Hawaiian bobtail squid Euprymna scolopes harbors a dense population of symbiotic, bioluminescent Vibrio fischeri in specialized light organs. An adult squid contains about 5 × 108 symbionts, and the light they produce provides counterillumination to help the squid avoid predation at night when it is foraging above the sand flats. The squid returns to the sand by daybreak, and at this time 95% of the symbiont population is expelled back into the environment. Assuming the remaining bacteria divide at a constant rate of growth, how many generations must take place to repopulate the organ by nightfall (12 hours later)? _____ generations 2) Based on your answer to Part 1, do you think the bacteria are dividing rapidly during the daytime? Find out by calculating the generation (doubling) time and enter it here: _____ minutes

#1: 4.32 #2: 167

1) How does R. palustris generate sufficient energy to make these repairs without carbon or nitrogen sources? A. R. palustris uses photosynthesis to generate a membrane potential that is then used to generate ATP for protein synthesis and DNA repair. B. R. palustris cells produce spores that germinate when nutrients become available. C. R. palustris cells become very small and therefore require less energy and fewer nutrients. D. R. palustris switches to photosynthesis to fix CO2, and after this step, cells can generate new components autotrophically. 2) The accompanying graph shows two identical cultures of R. palustris starved for carbon and oxygen. One of the cultures was kept in the dark (open black circles) while the other was exposed to light (closed red circles). Two weeks into the experiment there was a great difference in the number of viable cells in the two cultures. Which statement best summarizes the results of the experiment? A. The number of cells in the light exposed culture did not change over the course of one month while the number of cells in the dark culture dropped greatly over the first two weeks and did not recover. B. The number of cells in the dark culture did not change over the course of one month while the number of cells in the light exposed culture dropped greatly over the first two weeks and did not recover. C. The cells in the dark culture did not grow as fast as the cells in the light exposed culture. D. The cells in the light-exposed culture are in log phase while those in the dark are in stationary phase.

#1: A. R. palustris uses photosynthesis to generate a membrane potential that is then used to generate ATP for protein synthesis and DNA repair. #2. A. The number of cells in the light exposed culture did not change over the course of one month while the number of cells in the dark culture dropped greatly over the first two weeks and did not recover.

ILLUSTRATION Consider this image of colonies growing on MacConkey agar and then answer the following questions. 1) MacConkey agar is an example of a medium that is which of the following? Choose one or more. A. enriched with blood to support selected human pathogens B. selective for Gram-positive bacteria C. selective for Gram-negative bacteria D. differential based on ability to ferment lactose E. differential based on ability to ferment mannitol F. general purpose (suitable for Gram-negatives and Gram-positives) 2) MacConkey agar is most suitable for the cultivation of which of the following? A. enteric pathogens (such as Salmonella and Shigella) B. endospore formers (such as Bacillus) C. respiratory pathogens (such as Mycobacterium) D. nutritionally fastidious organisms (such as Neisseria) E. lactic acid bacteria (such as Lactobacillus and Streptococcus)

#1: C. selective for Gram-Negative bacteria D. differential based on ability to ferment lactose #2: A. enteric pathogens (such as Salmonella and Shigella)

1) In the marine environment, which types of organisms form the base of the food chain? A. photoheterotrophic microorganisms B. seaweeds C. heterotrophic microorganisms D. photoautotrophic microorganisms 2) Cyanobacteria do not rely on other organisms for nutrition, but they do depend on other organisms for waste product removal. Which cyanobacterial waste product can be toxic to them? A. oxygen B. glucose C. carbon dioxide D. urine

#1: D. photoautotrophic microorganisms #2: A. oxygen

1) Place the nine steps of the dilution streaking technique in the correct order. 2) The dilution streaking technique can take a bit of practice to master. Which of the following represent sources of error that would likely result in failure to obtain isolated colonies? Choose one or more. A. forgetting to sterilize the loop prior to obtaining the inoculum B. flaming the loop immediately after obtaining the bacterial sample C. forgetting to flame the loop before streaking sequential sections of the plate D. allowing the loop to cool for too long before proceeding E. not creating a small section of overlap across sequential sections 3) The dilution streaking technique is probably the most common procedure performed by microbiologists on a daily basis. It is not, however, particularly useful for A. calculating the concentration of viable cells in a culture. B. isolating colonies from a mixed culture containing different bacterial species. C. culturing bacteria that stick together or grow as chains or clusters (such as Streptococcus and Staphylococcus). D. transferring bacteria from a petri plate (as opposed to liquid culture as shown in the video).

#1: Sterilize the loop before obtaining bacterial inoculum, remove a sample from the culture flask, inoculate a section of the agar plate, flame the loop, streak cells from the 1st area into the 2nd, flame the loop, streak cells from the 2nd area into the 3rd, flame the loop, incubate the plate. #2: B. flaming the loop immediately after obtaining the bacterial sample C. forgetting to flame the loop before streaking sequential sections of the plate E. not creating a small section of overlap across sequential sections #3. A. calculating the concentration of viable cells in a culture.

1) Which of the following are characteristic of a vegetative cell, endospore, or both? OPTIONS: Uses central septation site Dipicolinic Acid Chromosomes Transcriptionally active Small acid soluble proteins Proteins Binary division Double membrane Ribosomes Metabolically active Resistant to heat, UV light, desiccation Peptidoglycan CATEGORIES: Vegetative Cell Endospore Both 2) Which of the following statements is NOT true of sporulation? A. The resultant endospores may remain viable for thousands of years. B. It represents an important form of reproduction for some bacterial species. C. The process is long and complex, requiring 8-10 hours. D. This capability is shared by many species of Gram-positive pathogens. E. Under favorable conditions, endospores can germinate and resume vegetative growth. 3) What is the role of dipicolinic acid in endospore formation? A. It aids in dehydration of the endospore and enhances heat resistance. B. It is the major component of the endospore cortex. C. It directs assymetrical septum formation. D. It lyses the mother cell during endospore release. E. It induces sporulation.

#1: Vegetative Cell: Uses central septation site Transcriptionally active Binary division Metabolically active Endospore: Dipicolinic Acid Small acid soluble proteins Double membrane Resistant to heat, UV light, desiccation Both: Chromosome Proteins Ribosomes Peptidoglycan #2: B. It represents an important form of reproduction for some bacterial species. #3: A. It aids in dehydration of the endospore and enhances heat resistance.

1) Pseudomonas aeruginosa represents a well-studied model organism for single-species biofilm formation. This research is also of direct medical significance because of the propensity of these bacteria to form biofilms in the _______ of patients with cystic fibrosis. 2) Which of the following early events in biofilm formation by Pseudomonas aeruginosa involves the extension and retraction of a specific pilus? A. quorum sensing B. twitching motility C. tethering adjacent cells together D. extracellular matrix production E. genetic exchange between cells 3) Mature biofilms of Pseudomonas aeruginosa produce flagellated cells for what purpose? A. to increase water and nutrient flow through biofilm channels via flagellar rotation (like a mini motor) B. to escape grazers that may be foraging on the biofilm C. There is no real "purpose." Because of random mutations, some revert to a flagellated form. D. to go in search of new places to colonize E. to provide additional elevation to the biofilm towers (the flagella act as stalks)

#1: lungs #2: B. twitching motility #3: D. to go in search of new places to colonize

Under optimal conditions, one E. coli cell can become two cells every A. 20 to 30 minutes. B. 2 to 3 hours. C. 2 to 3 minutes. D. 2 to 3 days.

A. 20 to 30 minutes.

The FepCGD complex is a type of A. ABC transporter. B. symporter. C. PTS transporter. D. facilitated diffusion transporter. E. porin.

A. ABC transporter.

Which of the following describes media and conditions that will be selective for nitrogen-fixing organisms? A. Media lack any nitrogen-containing compounds, but N2 is present in the atmosphere. B. Media contain ammonium ion, NH4+, as well as a dye that turns cells red when they reduce nitrogen gas (N2) into ammonium ion. C. Media lack any nitrogen-containing compounds, and there is no N2 present in the atmosphere. D. Media lack amino acids but contain ammonium ion, NH4+.

A. Media lack any nitrogen-containing compounds, but N2 is present in the atmosphere.

Cellular synthesis of which of the following would be directly affected by nitrogen limitation? Choose one or more. A.Nucleotides B.Amino acids C.Fatty acids D.Simple sugars

A. Nucleotides B. Amino acids

Which of the following is a mechanism used to store energy for later use in bacterial cells? A. Proton motive force B. CO2 C. NADH D. cAMP

A. Proton motive force

While adding nutrients to a culture medium in a glass container, which of the following would LEAST likely need to be added? A. Zinc B. Magnesium C. Phosphorous D. Nitrogen

A. Zinc

A bacterium produces a toxic metabolic by-product that it needs to efflux to the environment against the toxin's concentration gradient. The energy to drive this efflux comes from the electrochemically favorable influx of protons. This is an example of A. antiport. B. ABC transport. C. facilitated diffusion. D. symport.

A. antiport.

With respect to counting cells, a "viable" bacterium is one that A. can replicate and form a colony on a solid media surface. B. is capable of being infected by a bacteriophage. C. can scatter light and be detected by optical density. D. consumes oxygen via aerobic respiration.

A. can replicate and form a colony on a solid media surface.

Suppose you want to isolate E. coli mutants incapable of synthesizing the amino acid arginine. You grow mutagenized bacteria on a master plate of complete media and make a replica plate (by pressing a velvet block onto the master plate and then pressing it onto the replica plate—bacteria will be transferred) on media lacking arginine. Colonies that grew on the master plate but not the replica plate are arginine-synthesizing mutants. In this example, the replica plate A. contains selective media. B. is a liquid media culture condition. C. contains complex media. D. contains differential media.

A. contains selective media.

ILLUSTRATION The figure below shows the developmental cycle of Streptomyces coelicolor. The structures formed are analogous to A. fruiting bodies. B. endospores. C. eukaryotic fungi. D. heterocysts.

A. eukaryotic fungi.

The figure below shows the growth of bacteria inoculated into a new culture medium. The correct order of phases of growth is A. lag, log, stationary, death. B. stationary, log, lag, death. C. lag, stationary, log, death. D. log, lag, stationary, death.

A. lag, log, stationary, death.

A continuous culture differs from a batch culture because in continuous culture, A. new medium is added and old culture removed. B. the temperature continuously increases. C. the flask is continuously shaken. D. the temperature is held constant.

A. new medium is added and old culture removed.

Suppose a bacterium was exposed to a chemical that poisoned its cytochrome oxidase. Which of the following transport processes would be affected first? A. the lactose symporter (LacY) B. ABC transporters C. the phosphotransferase system D. sodium antiporters E. facilitated diffusion

A. the lactose symporter (LacY)

Bacteria as a group are incredibly metabolically diverse, but individual species are often highly specialized to reduce competition in their natural environment. This results in these species being unculturable because A. their growth may depend on necessary growth factors provided by other organisms in their natural environment. B. trace elements in the water used in the laboratory prevent their growth. C. they cannot tolerate oxygen. D. components in laboratory media are toxic to them.

A. their growth may depend on necessary growth factors provided by other organisms in their natural environment.

If an organism has a mean growth rate constant (k) of 1/hour, then the mean generation time, g, is A. impossible to determine. B. 60 minutes. C. 120 minutes. D. 30 minutes.

B. 60 minutes.

Which of the following statements is true? A. Only eukaryotes, and not prokaryotes, can undergo cell differentiation. B. Bacteria can undergo cell differentiation in response to an environmental stress. C. Bacterial cell differentiation produces only small changes in morphology. D. Bacteria can undergo cell differentiation without a change in gene expression.

B. Bacteria can undergo cell differentiation in response to an environmental stress.

Which of the following is true of cells in batch culture? A. Metabolic wastes do not accumulate. B. Cells will not remain at a constant mass. C. New batches of media are added during culturing. D. Cells never reach exponential growth rates.

B. Cells will not remain at a constant mass.

Which of the following is true of endospores? A. Endospores are produced from vegetative cells when nutrients are abundant. B. Endospores are resistant to many stresses that would kill vegetative cells. C. All bacterial species can produce endospores. D. Endospores can only germinate into viable vegetative cells within 10 years.

B. Endospores are resistant to many stresses that would kill vegetative cells.

A local golf course is notorious for using many different chemicals on their grass to get that perfect lawn. Concerns about the effects of these chemicals has led you to sample soils from the golf course and adjacent lots so that you can compare the microbial communities. Which of the following techniques will allow you to separate the culturable species to compare the samples for species richness? A. FACS B. Spread plating serial dilutions of the samples on generalized growth medium C. Growth in broth culture D. Growth in an enriched medium similar to the fertilizers used

B. Spread plating serial dilutions of the samples on generalized growth medium

Some bacteria live in deep sea vents where no light penetrates, yet are still capable of producing their own reduced carbon. These organisms are classified as A. photoautotrophs. B. chemoautotrophs. C. photoheterotrophs. D. chemoheterotrophs.

B. chemoautotrophs.

A new E. coli permease is discovered that moves an uncharged sugar molecule into the cell along with a proton. This new permease can be classified as an A. electrogenic antiporter. B. electrogenic symporter. C. electroneutral symporter. D. electroneutral antiporter.

B. electrogenic symporter.

One method for counting only the cells that express a particular protein on their cell surface is A. colony formation counts. B. fluorescent activated cell sorting (FACS). C. the Coulter counter. D. direct counting with a microscope.

B. fluorescent activated cell sorting (FACS).

Suppose you were interested in the effect of breastfeeding versus formula feeding on the composition of gut flora in newborns. As part of your experiment, stool samples from healthy babies in the study get plated on various agar media. You notice that greater numbers of colonies are recovered when samples are plated on blood agar compared to Luria Bertani (LB) agar. After some diligent subculturing, you isolate several bacterial species capable of slow growth on the blood but not on the LB agar. You correctly surmise that these organisms A. are Gram-positive and, thus, inhibited by the ingredients in LB agar. B. have extensive and complex nutritional requirements not met by LB agar. C. are opportunistic blood pathogens. D. should be classified as beta-hemolytic. E. grow because the blood agar suppresses the growth of faster-growing bacteria.

B. have extensive and complex nutritional requirements not met by LB agar.

Siderophores are responsible for helping bacteria acquire A. calcium. B. iron. C. ammonium ions. D. phosphorus.

B. iron.

Biofilms A. are relatively rare. B. may cause health problems for humans. C. contain only a single species of bacteria. D. are flat, two-dimensional films of bacteria.

B. may cause health problems for humans.

The heterocyst cells of cyanobacteria are specialized for A. antibiotic production. B. nitrogen fixation. C. photosynthesis. D. gliding motility.

B. nitrogen fixation.

Membranes prevent movement of most substances between the cell and the environment, but most required substances can be moved A. by ingesting them. B. through proteins embedded in the membrane that "recognize" specific substrates and allow their passage. C. by capturing the substances in specialized pockets of the membrane. D. by simple diffusion.

B. through proteins embedded in the membrane that "recognize" specific substrates and allow their passage.

ILLUSTRATION Examine the art, then complete the following sentences. This is an example of _______, which uses energy from a _______. The blue squares represent the substrate being _______. *CELLS MOVING FROM THE OUTSIDE TO THE INSIDE OF THE CELL MEMBRANE*

Blank 1: antiport Blank 2: a chemical gradient Blank 3: imported

A food worker was preparing some macaroni salad on the same counter on which he had cut up some raw chicken. Suppose this resulted in the accidental introduction of 380 cells of E. coli into the 1 gallon container of macaroni. This careless worker then left it unrefrigerated until 6 hours later. Now consider that E. coli has a doubling (generation) time of 20 minutes when grown in a rich medium. Assuming the cells were dividing at their maximum rate in the macaroni salad, what would the level of bacterial contamination be by the time it was finally refrigerated? _____ cells

Blank: 9.96 X 10^7

Crop rotation (alternating planting of grains and legumes) has been practiced for thousands of years, long before anyone understood the contribution of _______ to enhancing soil fertility.

Blank: symbiotic nitrogen fixers

Which of the following statements is true? A. Bacterial species use a limited number of nutrient sources. B. Most bacterial species can be cultured in the lab. C. All organisms require carbon as a macronutrient. D. All bacterial species require the same nutrients for growth.

C. All organisms require carbon as a macronutrient.

Which of the following is true of complex media? A. Complex media are the most difficult of all to prepare. B. Complex media can help determine the metabolic capacity of an organism. C. Bacteria grow faster on complex media than on synthetic media. D. All the components and their concentrations are known.

C. Bacteria grow faster on complex media than on synthetic media.

Nitrogen-fixing bacteria A. are not involved in the nitrogen cycle. B. are all found in the ocean. C. can convert atmospheric nitrogen into ammonium ions. D. are all symbionts with legumes.

C. can convert atmospheric nitrogen into ammonium ions.

Organisms that need to ingest reduced carbon are called A. phototrophs. B. lithotrophs. C. heterotrophs. D. autotrophs.

C. heterotrophs.

The major factor limiting bacterial growth in nature is A. oxygen. B. temperature extremes. C. nutrients. D. antibacterial agents. E. space.

C. nutrients

Glucose uptake against a bacterium's concentration gradient A. is simple because glucose can directly cross the plasma membrane. B. will require a glucose transport protein but no energy expenditure. C. will require a glucose transport protein and will also expend energy. D. is impossible because a bacterium cannot accumulate a nutrient at a higher concentration inside the cell than is present in the environment.

C. will require a glucose transport protein and will also expend energy.

If a bacterium can divide once an hour, then after 5 hours, 1 bacterium will have yielded __________ bacteria. A. 50 B. 5 C. 10 D. 32

D. 32

An essential nutrient is one that A. is not needed by the bacteria for proper growth. B. is always plentiful in the environment. C. bacteria need for proper growth and can make themselves. D. bacteria need for proper growth but cannot make themselves.

D. bacteria need for proper growth but cannot make themselves.

Suppose you have isolated a compound that alters the quorum signal of Pseudomonas aeruginosa, such that it cannot interact with its normal receptor. Bacterial cells targeted by such a disrupter would most likely A. be unable to turn off twitching motility. B. be unable to respond to settling cues. C. be nonmotile. D. be similar to free-living cells in their sensitivity to antibiotics. E. retain their flagella after surface contact.

D. be similar to free-living cells in their sensitivity to antibiotics.

Quorum sensing A. occurs in the gut to signal hunger. B. triggers endospore formation. C. triggers washout in continuous culture. D. coordinates biofilm formation via chemical signaling among cells.

D. coordinates biofilm formation via chemical signaling among cells.

You have isolated a mutant strain of Bacillus subtilis (which you designate wimP) whose endospores can be killed by boiling water. When you analyze the endospores produced by this strain, you find that compared to endospores produced by the parent (a wild-type strain), the wimP spores have significantly A. reduced amounts of germination factors. B. lower amounts of spore coat proteins. C. elevated amounts of germination factors. D. higher water content. E. reduced amounts of small acid-soluble proteins.

D. higher water content

Choose the pair of words that correctly completes the following sentence: Biofilms preferentially form in __________ environments with __________ levels of nutrients. A. dry / high B. dry / low C. moist / low D. moist / high

D. moist / high

Nitrogen fixation is the conversion of A. ammonium ions to nitrogen gas. B. nitrate ions to nitrogen gas. C. ammonium ions to nitrate ions. D. nitrogen gas to ammonium ions.

D. nitrogen gas to ammonium ions.

Coupled transport to move nutrients into the cell against their concentration gradients is most likely to occur as the electrical gradient moves A. water into or out of the cell. B. positive ions out of the cell. C. negative ions into the cell. D. positive ions into the cell.

D. positive ions into the cell.

Biofilms form A. to cause disease. B. in any liquid substrate. C. in response to environmental stress. D. to establish a collaborative community that promotes the members' growth and reproduction.

D. to establish a collaborative community that promotes the members' growth and reproduction.

Permeases, periplasmic nutrient-binding proteins, and membrane-spanning pores (porins) all function to A. export cellular waste products. B. help transport gases such as carbon dioxide and oxygen into the cell. C. assist in the active pumping (efflux) of antibiotics from the cell. D. couple nutrient transport to the hydrolysis of phosphoenolpyruvate. E. assist in the uptake of molecules too big or polar to diffuse across lipid bilayers.

E. assist in the uptake of molecules too big or polar to diffuse across lipid bilayers.

Which of the following would not be included in the formulation of a defined medium? A. potassium phosphate B. glucose C. magnesium sulfate D. sodium chloride E. tryptone

E. tryptone