Microbiology 521 Final Examination, Winter Quarter 1997

For questions 1-6, choose from among the genera listed below.

• (A) Anabaena
• (B) Pseudomonas
• (C) Rhizobium
• (D) Staphylococcus
• (E) Thiobacillus

An organism from this genus

1. Acquires energy from chemolithotrophic oxidation using hydrogen sulfide. E
2. Belongs to a phylum of bacteria responsible for the precipitation of iron from seawater. A
3. Is exploited for the degradation of xenobiotics. B
4. Is used for mining. E
5. Lives symbiotically with leguminous plants, within nodules. C
6. Might poison a cream doughnut that is several days old. D

For questions 7 - 10, consider the following reactions of the biogeochemical cycles:

7. Which reaction(s) are used by microorganisms only under anoxic conditions?

(a) N only.
(b) G and O.
(c) B, K, and N.
(d) F, J, and O.
(e) E, F, J, K, and N.

8. Which of the half reactions shown above are reductions?

(a) C and G.
(b) C and L.
(c) B, K, and M.
(d) D, K, and M.
(e) K, N, and O.

9. A monooxygenase is involved in

(a) L only.
(b) C and L.
(c) L and M.
(d) I, L, and M.
(e) C, D, E, and M.

10. The reaction(s) that fix the atoms of a gas into a form useful to animals are

(a) A and L.
(b) A and N.
(c) H and L.
(d) L and O.
(e) N and O.

11. You have identified a narC^- strain of E. coli. You wish to use this strain to clone the narC gene, encoding nitrate reductase, by complementation. Complementation could be:

(a) Accomplished by insertion of a lambda expression library of wild type E. coli DNA, provided that the narC^- strain is also recA^-.
(b) Accomplished by insertion of a lambda expression library of wild type E. coli DNA, provided that the narC^- strain is also recA⁺.
(c) Accomplished by generalized transduction using a P1 phage carrying wild-type E. coli DNA, provided that the narC^- strain is also recA^-.
(d) Detected by anaerobic growth on media containing nitrate as the sole electron acceptor.
(e) (a) and (d) only.

12. The greenhouse effect is increased by the action of:

(a) Fast growing algae that synthesize storage lipids as a large fraction of their weight.
(b) Methane monooxygenase.
(c) Methanogens.
(d) Methanotrophs.
(e) RubisCO.

13. Consider the production of acetate and hydrogen from Syntrophomonas and the conversion of acetate to methane by some methanogens, as follows:

It is true that:

(a) Both reactions occur in the rumen.
(b) The overall conversion of butyrate to CH₄ and HCO₃^- has a favorable delta G^o = - 13.8 kJ.
(c) The overall reaction would only be favorable if the H₂ and HCO₃^- produced were also converted to methane.
(d) The Syntrophomonas reaction is favorable.
(e) (a) and (c) only.

14. Symbiosis is illustrated by the relationship(s) of:

(a) Nitrosofying bacteria and nitrifying bacteria.
(b) Rhizobia and legumes.
(c) Thiovolum and the giant tube worm Riftia in deep-sea thermal vents.
(d) (b) and (c) only.
(e) (a), (b), and (c).

15. Microbial strategies discussed in class for protecting nitrogenase from oxidative damage do not include:

(a) Binding of O₂ to the FixL protein.
(b) Housing of the nitrogenase in specialized cells called heterocysts.
(c) Increased aerobic respiration.
(d) Increased phosphorylation of the transcription factor FixJ.
(e) Use of leghemoglobin.

16. An increasing number of states in the U.S. are relaxing zoning laws to allow large-scale hog farms (that raise > 10,000 hogs) to dump their wastes directly into rivers without treatment. Given that hogs produce two and half times more waste per day than adult humans, this would be expected to lead to:

(a) Increase in hydrogen sulfide in nearby rivers.
(b) Rapid growth of some microorganisms in nearby rivers.
(c) Reduction in oxygen in nearby rivers.
(d) (b) and (c) only.
(e) (a), (b), and (c).

17. Consider the following organic compounds:

Which one(s) would be degraded to smaller molecules under oxic conditions?

(a) Compound A only.
(b) Compound B only.
(c) Compounds A and C only.
(d) Compounds D and E only.
(e) All of the above.

18. The level of nitrate in drinking water has been rising over time. Which of the following contributes to this increase?

(a) Denitrifying bacteria.
(b) Dumping of wastewater that has received secondary but not tertiary treatment.
(c) The inhibitor of the nitrosofiers, nitrapyrin.
(d) Nitrifying bacteria.
(e) (b) and (d) only.

19. The following organism(s) would render a mercury spill more toxic.

(a) Methanogens
(b) Pseudomonas species carrying the R100 plasmid
(c) Sulfate reducers
(d) Thiobacillus
(e) All of above

20. A suitable habitat for a sulfate reducing bacterium is

(a) Improperly treated canned foods.
(b) The rumen.
(c) The sediment at the bottom of a shallow sea.
(d) A sludge digestor.
(e) All of the above.

21. Healthy human adults

(a) Are as succeptible as healthy infants to food infections.
(b) Are more succeptible than healthy infants to Vibrio cholera in polluted waters.
(c) Are poisoned by the nitrate in honey.
(d) Can eat honey containing spores of Clostridium botulinum without becoming ill.
(e) Have a less acidic stomach than healthy human infants.

22. Protozoa

(a) Are easily killed in their cyst phase by chlorination.
(b) Are unicellular autotrophs with many specialized structures.
(c) Can reach 50 meters in length.
(d) Have not influenced human evolution.
(e) Prey on bacteria in the rumen.

23. The delta ¹⁸O (isotopic fractionation) for the oxygen in Earth's atmosphere

(a) Is negative.
(b) Is zero.
(c) Is positive.
(d) Is equal to 1.
(e) Cannot be determined.

24. Which of the following is true?

(a) During aging, wines become more acidic.
(b) Fermentation of sugars by Saccharomyces species is done in wine but not in beer production.
(c) In beer making, the malt provides the amylases required for the degradation of starch.
(d) Souring of wines by Acetobacter species involves an anaerobic fermentation.
(e) None of the above.

25. A Dutch waste treatment plant purifies wastewater using three levels of treatment, completely recycling the water.

During BOD determinations, the measurements of the oxygen content were as follows:

Sample Untreated After primary treatment Secondary treatment

Oxygen (mg/L) 2.0 6.0 9.2

Assume that at 20^oC the oxygen content of pure water saturated with oxygen is 10 mg/L. What is the percent decrease in BOD relative to the untreated sample after:

a. Primary treatment? 50%.

b. Secondary treatment? 90%.

c. A coliform test was done following tertiary treatment. Why? (Please write no more than one sentence.)

c. To assay for pathogens, because coliforms are indicator organisms for the presence of fecal pathogens.

State which level of treatment (primary, aerobic secondary, anaerobic secondary, tertiary) would:

d. Remove the bulk of the phosphate. Tertiary.

e. Employ Zooglea ramigera. Secondary aerobic.

f. Employ methanogens. Secondary anaerobic.

g. Oxidize xenobiotics. Tertiary.

26. The serine pathway shown in Figure 19.32 (and in the exam) is an altenative method of carbon fixation used by some methanotrophic bacteria.

Is this a net oxidation or reduction of carbon?

a. Reduction

What is the carrier of the electrons?

b. NADH

Identify the two preexisting molecules to which the entering carbon is affixed:

c. Glycine

d.Phosphoenolpyruvate

What is the source of the activating power?

e. ATP

Would this cycle be found in an autotroph or a heterotroph?

f. Autotroph

27. A classmate has provided you with a plasmid for expression in E. coli of the gene encoding methane monooxygenase. That gene is cloned downstream of the lambda P_R promoter. The same plasmid also carries the gene encoding the temperature-sentitive lambda repressor (repressor active at 30^oC, inactive at 42^oC) downstream from a constitutive promoter. Assuming that the growth of E. coli is slowed by the expression of methane monooxygenase:

How can the expression of methane monooxygenase be avoided during growth of the cells?

a. Grow at 30^oC.

How can expression of the gene encoding methane monooxygenase be induced?

b. Induce at 42^oC.

The enzymatic activity of methane monooxygenase can be directly measured.

What are the two substrates in the reaction?

c. Methane (CH₄)

d. Oxygen (O₂)

What is the carbon containing product?

e. Methanol (CH₃OH)

How can radioisotopes be exploited for measuring methane monooxygenase activity? (Please write no more than one sentence.)

f. Provide ¹⁴C-labeled methane, and measure the decrease in radiolabeled methane or the production of radiolabeled methanol.

What type of heterotrophic organism is the likely original source of the gene encoding methane monooxygenase? Be specific.

g. A methanotroph.

In what habitat would this organism (in part g) be found? Address your discussion especially to oxygen. (Please write no more than one sentence.)

h. At the boundary of oxic and anoxic habitats, where both the diffused CH₄ from methanogens as well as diffused O₂ can be obtained.