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

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 by use of formate, lactate, pyruvate, or H 2 as the electron donor. Furthermore, strain S12 grew to a maximal density of 3.0 ؋ 10 7 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 the 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 H 2 as the electron donor. The presence of 5 M Cu 2؉ ions, 200 M dicumarol, 100 M stigmatellin, and 100 M 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.

Role of iron in azoreduction by resting cells of Shewanella decolorationis S12

“…Shewanella decolorationis S12, previously isolated from activated sludge of a textile-printing wastewater treatment plant in Guangzhou, China (Xu et al 2005), can also effectively reduce azo dyes with many organic substances and hydrogen as electron donors (Hong et al 2007a). The dissimilatory azoreduction of S. decolorationis S12 is a process linked to bacterial electron transport chain and has been proved to be a new form of microbial anaerobic respiration (azorespiration) (Hong et al 2007c(Hong et al , 2009). Further studies have found that the breakdown products of azo dyes can be completely mineralized under microaerophilic or aerobic conditions by S. decolorationis S12 (Hong et al 2007b;Xu et al 2007b).…”

Physiology and biochemistry of reduction of azo compounds by Shewanella strains relevant to electron transport chain

“…The disappearance of amaranth (azo reduction) was accompanied by stoichiometrical consumption of formate over time of incubation. Based on the calculation, formate consumption and amaranth reduction were in good agreement for the following reaction: Ar1– N  =  N –Ar 2  + 2COOH– + 2H 2 O → Ar1–NH 2  + H 2 N–Ar 2  + 2HCO 3 −  + 2H + (Hong et al 2007a). In addition, both Shewalella sp.…”

Electricity Generation by Shewanella decolorationis S12 without Cytochrome c

“…In addition to electricity generation, riboflavin-stimulated EET were also founded in Fe(III) and amaranth (an cell membrane-impermeable azo dye; Hong et al, 2007) reduction of MT-S12 biofilms (Supplementary Figure S4). These results suggested that although OMCs were eliminated, the electron transfer from MT-S12 to electrode could also be stimulated by higher concentration of electron mediators.…”