This is in agreement with recent studies indicating the existence of links between cysteine and/or cysteine-containing molecules and oxidative stress defense in several bacteria (Hung et al., 2003; Park & Imlay,
2003; Hochgrafe et al., 2007). Our results further support the pleiotropic role of CymR in Firmicutes (Even et al., Lumacaftor 2006; Soutourina et al., 2009). We are grateful to A. Danchin for helpful discussions. We thank P. Courtin for metabolite analysis. I.M.-V. and O.S. are full and assistant professors at the Université Paris 7, respectively. Research was supported by grants from the Centre National de la Recherche Scientifique (CNRS BYL719 datasheet URA 2171), the Institut Pasteur (PTR N°256) and the Agence Nationale de
la Recherche (EcoMet program, ANR-06-PNRA-014). “
“A species of Dechlorospirillum was isolated from an Fe(II)-oxidizing, opposing-gradient-culture enrichment using an inoculum from a circumneutral, freshwater creek that showed copious amounts of Fe(III) (hydr)oxide precipitation. In gradient cultures amended with a redox indicator to visualize the depth of oxygen penetration, Dechlorospirillum sp. strain M1 showed Fe(II)-dependent growth at the oxic–anoxic interface and was unable to utilize sulfide as an alternate electron donor. The bacterium also grew with acetate
as an electron donor under both microaerophilic and nitrate-reducing conditions, but was incapable of organotrophic Fe(III) reduction or nitrate-dependent Fe(II) oxidation. Although members of the genus Dechlorospirillum are primarily known as perchlorate and nitrate reducers, our results suggest that some species are members of the microbial communities involved in iron redox cycling at the oxic–anoxic transition zones in freshwater sediments. Redox cycling of iron in aquatic systems can be closely Pyruvate dehydrogenase lipoamide kinase isozyme 1 tied to biogeochemical transformations of C, N, and other elements, in addition to being involved in pollutant transformation and mobility (Lovley, 2000; Picardal & Cooper, 2005; Roden & Emerson, 2007). Because of the rapid, abiotic oxidation of Fe2+ by oxygen (O2) in aqueous systems (Stumm & Lee, 1961), Fe(II)-oxidizing bacteria (FeOB) at a circumneutral pH typically are found in greatest numbers in environments where dissolved O2 concentrations are sufficiently low, for example, <5% of air-saturated values, to minimize abiotic reaction rates relative to the rates of biological catalysis (Emerson et al., 1999; Emerson & Moyer, 2002; Neubauer et al., 2002; Emerson & Weiss, 2004).