Biodegradation of chlorinated compounds at interfaces and biodegradation of 4-nitroaniline
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Most microbial activity in nature takes place at interfaces where redox discontinuities are present. Organic pollutants in groundwater encounter oxic/anoxic interfaces when they emerge to surface water bodies or volatilize above the plume. Such oxic/anoxic interfaces are key habitats for aerobic bacteria and are in turn created by the bacteria that degrade organic electron donors. In the absence of biodegradation, synthetic pollutants can migrate from the plume and impact a variety of receptors. The aims of our study were to determine whether microbes at oxic/anoxic interfaces can use synthetic chemicals as electron donors and protect the overlying vadose zone or surface water from groundwater pollutants. The approach was to design columns representing the interfaces and measure activities of the microbial communities responsible for the biodegradation of synthetic compounds.Taken together the above studies established clearly that contaminants recalcitrant under anaerobic conditions but degradable under aerobic conditions can be biodegraded at the narrow oxic/anoxic interface resulting in the protection of the overlying soil or water. The findings provide the basis for new approaches to natural attenuation that can serve to dramatically reduce the cost of bioremediation actions. Synthetic chemicals are widespread in the environment because of their extensive use in industry. These chemicals were recalcitrant until their microbial degradation pathways evolved. Currently the biodegradation pathways of many synthetic chemicals are known and serve as the basis for bioremediation strategies. The second part of the research described here involved discovery of the aerobic degradation pathway of a dye additive: 4-nitroaniline (4NA). Annotation of the whole genome sequence coupled with assays and supported with cloned enzymes revealed that the 4NA biodegradation pathway contains two monooxygenase steps prior to ring cleavage. Because nitroaniline degradation was not previously understood our work advanced the understanding of metabolic diversity in degradation of amino and nitro compounds by providing enzymes with unique activities.