Soil Microbiology and Biochemistry



Soil Microbiology and Biochemistry

Soil Sci./Bact. 523 Exam III

due May 12, 2005

Name:____________________

1. You are an environmental scientist for AgroSci Inc. The company has developed a compound that shows promise in controlling a variety of insects and is potentially valuable for improving production of several types of crops. Before product development goes further, the company needs to know more about the environmental fate of the compound, and has given this job to you. (20 pts)

Explain how you would determine if the compound if the compound is persistent or non-persistent in the environment? What factors would be important to consider?

If the compound is non-persistent, how would you determine the role or contribution biological processes have in the process?

If microbiological processes prove important, how would you determine the contribution of growth-based vs. cometabolic transformations

If cometabolic transformations occur, How would you distinguish Type I vs. Type II processes?

2. In the US, sites that pose some of the worst contamination problems and deemed to be in greatest need of remediation are identified on the Superfund National Priorities List (). Polycyclic aromatic hydrocarbons (PAH) are major contaminants in at least half of these sites, and therefore one of the major classes of compounds that remediation needs to target. At many of these sites, PAH are present in tars or oily substance that are mixtures of many different compounds (e.g., benzene, alkylaromatics, aliphatic hydrocarbons). The PAH, as well as tars and oils, occur in surface soils, groundwater and sediments. The estimated costs for clean-up of these PAH sites is conservatively put at $4 billion (). Bioremediation might be used in these operations, and could be substantially less expensive than the standard approaches. However, bioremediation has so far meet with limited success at best. Answer the following questions. (20 pts)

i) Explain the mechanisms by which PAH are biodegraded.

ii) Discuss the at least three factors that would limit PAH biodegradation in the environment

iii) Design an approach you might explore to apply bioremediation for PAH clean-up and overcome the limitations you’ve identified.

3. Given the choice of three mechanisms (growth-supporting, Type 1 cometabolism, Type 2 cometabolism) by which and organic contaminant might be degraded, which would you choose to stimulate and why? Explain how this question applies to bioremediation of chlorinated solvents such as PCE. 10 pts

4. Compare and contrast the microbes and microbial processes that would be underlying the degradation or biotransformation of toluene and polychlorinated biphenyls in an aerobic surface soil and in an anaerobic sediment. Discuss a) the possibilities for both growth-based and cometabolic transformations, b) the metabolic basis for each process, c) what limit growth or cometabolic degradation in each case, and d) examples of organisms (genus names or physiological groups) that may mediate the growth-based or cometabolic biotransformations. 10 pts

5. Two general forms of bioremediation are “intrinsic” and “enhanced”. Please define each of these and compare and contrast their similarties and differences. 10 pts

6. How would approaches for enhancing degradation of hydrocarbons in surface soil differ from that applied to anaerobic groundwater? 10 pts

7. Explain how soil vapor extraction (SVE) is used to remediate subsurface soils contaminated with hydrocarbons. How does Bioventing differ from SVE? 10 pts

8. What is in situ respirometry (ISR)? Explain how this is used to assay microbial activity and to estimate amounts of hydrocarbon biodegradation. What are the benefits of the ISR measurements? What are some of limitations of the hydrocarbon biodegradation estimates made from ISR? 10 pts

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