Physiology of Microbial Perchlorate Reduction

Physiology of Microbial Perchlorate Reduction

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During the course of five years, my research focused on the physiology of the dissimilatory perchlorate-reducing bacteria (DPRB) with a special interest on the effect of nitrate on the microbial perchlorate reduction. First, the taxis response toward nitrate and perchlorate by three representative DPRB was investigated. All three DPRB tested were positive for taxis behavior toward perchlorate using both agar-based and capillary-based chemotaxis assays. Description of taxis response in Azospira spirillum strain PS revealed possibly the only known perchlorate reductase unable to use nitrate as a substrate. Second, periplasmic nitrate reductase was established as the only dissimilatory nitrate reductase in Dechloromonas aromatica strain RCB. However, in the absence of the periplasmic nitrate reductase, perchlorate reductase, with nitrate-reducing capability, was found to partially support anaerobic growth on nitrate. Investigations into the mechanism of oxygen removal during perchlorate reduction revealed that chlorite could serve as a source for the electron acceptor, oxygen, to support the growth of strain RCB. Moreover, a cbb3-type cytochrome oxidase was proposed to be the oxygen reductase required for growth on perchlorate, a result indicating aerobic respiration by DPRB under anoxic conditions. Finally, preferential utilization of nitrate in the presence of perchlorate was established in strain RCB regardless of relative concentrations of nitrate and perchlorate or prior growth conditions of the cultures. However, in the absence of the periplasmic nitrate reductase, strain RCB displayed a concentration-dependent pattern of electron acceptor utilization. Based on both physiological characterizations and transcriptional analyses, a new model was proposed to demonstrate how DPRB establish preferential utilization of nitrate, a thermodynamically less favorable electron acceptor, to perchlorate.Introduction Perchlorate (CIO4 ) is a chlorine oxyanion with harmful complications in human health under prolonged ... As a result, the US Environmental Protection Agency set a reference dose for chronic oral perchlorate exposure atanbsp;...

Title:Physiology of Microbial Perchlorate Reduction
Author:Yvonne Sun
Publisher:ProQuest - 2008


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