Chapter 4 Microbiology

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 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

4.32;167

After watching the animation, place the nine steps of the dilution streaking technique in the correct order.

6. Flame the loop a third time and allow it to cool. 7. Using the loop, draw cells from the second area onto another fresh section of agar. 8. Sterilize the loop a final time. 9. Place the petri plate in the appropriate incubator.

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? ____x 10^___ cells

9.96;7

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?Choose one: A. oxygen B. carbon dioxide C. urine D. glucose

A

How does R. palustris generate sufficient energy to make these repairs without carbon or nitrogen sources? Choose one: 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 become very small and therefore require less energy and fewer nutrients. C. R. palustris cells produce spores that germinate when nutrients become available. D. R. palustris switches to photosynthesis to fix CO2, and after this step, cells can generate new components autotrophically.

A

In the marine environment, which types of organisms form the base of the food chain? A. photoautotrophic microorganisms B. photoheterotrophic microorganisms C. seaweeds D. heterotrophic microorganisms

A

MacConkey agar is most suitable for the cultivation of which of the following? Choose one: A. enteric pathogens (such as Salmonella and Shigella) B. lactic acid bacteria (such as Lactobacillus and Streptococcus) C. nutritionally fastidious organisms (such as Neisseria) D. endospore formers (such as Bacillus) E. respiratory pathogens (such as Mycobacterium)

A

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

A

What is the role of dipicolinic acid in endospore formation? Choose one: 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.

A

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 Choose one: A. higher water content. B. lower amounts of spore coat proteins. C. elevated amounts of germination factors. D. reduced amounts of germination factors. E. reduced amounts of small acid-soluble proteins.

A

MacConkey agar is an example of a medium that is which of the following? Choose one or more: A.selective for Gram-negative bacteria B.general purpose (suitable for Gram-negatives and Gram-positives) C.selective for Gram-positive bacteria D.differential based on ability to ferment lactose E.differential based on ability to ferment mannitol F.enriched with blood to support selected human pathogens

A,D

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

B

Mature biofilms of Pseudomonas aeruginosa produce flagellated cells for what purpose? Choose one: A. to escape grazers that may be foraging on the biofilm B. to go in search of new places to colonize C. to provide additional elevation to the biofilm towers (the flagella act as stalks) D. to increase water and nutrient flow through biofilm channels via flagellar rotation (like a mini motor) E. There is no real "purpose." Because of random mutations, some revert to a flagellated form.

B

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 Choose one: A. retain their flagella after surface contact. B. be similar to free-living cells in their sensitivity to antibiotics. C. be nonmotile. D. be unable to turn off twitching motility. E. be unable to respond to settling cues.

B

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 Choose one: A. should be classified as beta-hemolytic. B. have extensive and complex nutritional requirements not met by LB agar. C. are Gram-positive and, thus, inhibited by the ingredients in LB agar. D. are opportunistic blood pathogens. E. grow because the blood agar suppresses the growth of faster-growing bacteria.

B

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

B

Which of the following early events in biofilm formation by Pseudomonas aeruginosa involves the extension and retraction of a specific pilus?Choose one: A. tethering adjacent cells together B. twitching motility C. quorum sensing D. extracellular matrix production E. genetic exchange between cells

B

Which of the following statements is NOT true of sporulation?Choose one: 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.

B

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

B,C,E

The dilution streaking technique is probably the most common procedure performed by microbiologists on a daily basis. It is not, however, particularly useful for Choose one: A. culturing bacteria that stick together or grow as chains or clusters (such as Streptococcus and Staphylococcus). B. transferring bacteria from a petri plate (as opposed to liquid culture as shown in the video). C. calculating the concentration of viable cells in a culture. D. isolating colonies from a mixed culture containing different bacterial species.

C

Which of the following describes media and conditions that will be selective for nitrogen-fixing organisms? Choose one: A. Media lack any nitrogen-containing compounds, and there is no N2 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, but N2 is present in the atmosphere. D. Media lack amino acids but contain ammonium ion, NH4+.

C

Which organisms produce alginate, the substrate for the AguEFG transporter system of the marine microbe Thermotoga maritima? Choose one: A. E. coli B. land plants C. brown seaweeds D. Pseudomonas aeruginosa

C

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

C,D

How can purified siderophores from one bacterium be used to inhibit the growth of another bacterium? Choose one: A. The siderophores from one bacterium can overwhelm and inhibit the ABC transporters of the second bacterium. B. The siderophore from one bacterium can be toxic to the second bacterium. C. The siderophores from one bacterium can transport too much iron into the second bacterium, causing toxic side effects. D. The siderophores from one bacterium can absorb free iron in the media or surrounding environment, thereby depriving the second bacterium of the needed nutrient.

D

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

D

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? Choose one: A. 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. B. The cells in the dark culture did not grow as fast as the cells in the light exposed culture. C. The cells in the light-exposed culture are in log phase while those in the dark are in stationary phase. D. 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.

D

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

E

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

E

This is an example of _____________ , which uses energy from _____________________ gradient. The blue squares represent the substrate being ________________.

antiport;a chemical;imported

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.

lungs

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

symbiotic