Energy-conserving dimethyl sulfoxide reduction in the acetogenic bacterium Moorella thermoacetica

Moorella thermoacetica is one of the well-studied thermophilic acetogenic bacteria. It grows by oxidation of organic substrates, CO or H₂ coupled to CO₂ reduction to acetate. Here, we describe that M. thermoacetica can also use dimethyl sulfoxide as terminal electron acceptor. Growth of M. thermoacetica on glucose or H₂  + CO₂ was stimulated by dimethyl sulfoxide (DMSO). Membranes showed a DMSO reductase activity, that was induced by growing cells in presence of DMSO. The enzyme used reduced anthraquinone-2,6-disulfonate, benzyl- and methyl viologen as electron donor, but not NAD(P)H. Activity was highest at pH 5 and 60°C, the Km for DMSO was 2.4 mM. Potential DMSO reductase subunits were identified by peptide mass fingerprinting; they are encoded in a genomic region that contains three potential dmsA genes, three dmsB genes and one dmsC gene. Transcriptome analysis revealed that two different dmsAB gene clusters were induced in the presence of DMSO. The function of these two and their predicted biochemical features are discussed. In addition, the data are in line with the hypothesis that M. thermoacetica can use DMSO alongside CO₂ as electron acceptor and DMSO reduction is catalysed by an energy-conserving, membrane-bound electron transport chain with DMSO as final electron acceptor.