The fate and distribution of toxic metal ions in the environment can be affected by microbial activity under both aerobic and anoxic conditions. Unlike organic contaminants which can be completely detoxified by oxidation to carbon dioxide and water, toxic metals cannot be destroyed but are subject to a variety of changes mediated by bacteria which can alter their toxicity to other organisms as well as their availability to both biological and chemical processes. Bacterially mediated action on metals include oxidation, reduction, methylation, energy driven efflux pumps, intracellular sequestering, and extracellular binding and precipitation. The focus in this component will be directed specifically on chromium and cadmium as each figure prominently at the two sites of interest. It is proposed that chromium toxicity may be significantly altered by bacterially mediated reduction of the more toxic Cr(VI) to the less toxic Cr(III). Results we have obtained indicate that reduction by bacteria takes place under anaerobic conditions and that both toluene and pyruvate can serve as the electron donor and carbon source. Bacterial reduction of Cr(VI) is not well understood and its relative significance in the environment has not been addressed. The active cultures will be examined quantitatively for their rates and extent of transformation. The stoichiometry of substrate oxidation and Cr reduction will be determined. Additional sources from contaminated sites will be characterized for Cr reducing bacteria which are Cr resistant with the intention of seeking very active Cr reducers which are tolerant to high concentrations. These strains may be useful for clean-up and remediation purposes. Pure cultures of anaerobic species mediating these transformations will be isolated for further physiological, genetic and biochemical studies. For cadmium the major routes of resistance by bacteria is by efflux and by binding to the cell or cell products. It is proposed that bacteria in Foundry Cove which sequester or bind Cd would have the greatest impact on Cd bioavailability. Bacteria from the sediment will be screened for their resistance mechanisms and promising species will be isolated for further comparisons. Homology to known Cd resistance bearing plasmids will be examined with DNA hybridization techniques. In addition, the effect of capsular polysaccharides on bioavailability will be tested with Klebsiella aerogenes type 64 as the model organism and for which the capsular polysaccharide has been characterized. Amending K. aerogenes to a model ecosystem in the laboratory as a means of decreasing Cd levels in the environment and to the biota will be tested in conjunction with Component 9.
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