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Appl. Environ. Microbiol. doi:10.1128/AEM.01415-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Respiration and Growth of Shewanella decolorationis S12 with Azo Compound as Sole Electron Acceptor

Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Institute of Microbiology, Guangzhou 510070, China; South China Institute of Botany, Chinese Academy of Science, Guangzhou 510650, China; Graduate School of the Chinese Academy of Sciences, Beijing 100039, China

^* To whom correspondence should be addressed. Email: guopingsun{at}163.com.

	Abstract

The ability of Shewanella decolorationis S12 to obtain energy for growth by coupling the oxidation of various electron donors to dissimilatory azoreduction was investigated. This microorganism can reduce a variety of azo dyes using formate, lactate, pyruvate or HB_2B as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0x10⁷ cells per ml after compete reduction of 2.0 mM amaranth in a defined medium. This was accompanied by a stoichiometric consumption of 4.0 mM formate over time when amaranth and formate were supplied as sole electron acceptor and donor, respectively, suggesting that microbial azoreduction is an electron transport process, and that this electron transport can yield energy to support growth. Purified membranous, periplasmic and cytoplasmic fractions from S12 were analyzed, but only the membranous fraction was capable of reducing azo dyes with formate, lactate, pyruvate or HB_2B as the electron donor. The presence of 5 µM Cu²⁺ ions, 200 µM dicumarol, 100 µM stigmatellin and 100 µM metyrapone inhibited anaerobic azoreduction activity by both whole cells and the purified membrane fraction, showing that dehydrogenases, cytochromes and menaquinone are essential electron transfer components for azoreduction. These results provide evidence that the microbial anaerobic azoreduction is linked to the electron transport chain and suggest that the dissimilatory azoreduction is a form of microbial anaerobic respiration. These findings not only expand the number of potential electron acceptors known for microbial energy conservation, but also elucidate the mechanisms of microbial anaerobic azoreduction.