Genes involved in hydrogen and sulfur metabolism in phototrophic sulfur bacteria

The dsr genes and the hydSL operon are present as separate entities in phot otrophic sulfur oxidizers of the genera Allochromatium, Marichromatium, Thi ocapsa and Thiocystis and are organized similarly as in Allochromatium vino sum and Thiocapsa roseopersicina, respectively. The dsrA gene, encoding the a subunit of 'reverse' siroheme sulfite reductase, is also present in two species of green sulfur bacteria pointing to an important and universal rol e of this enzyme and probably other proteins encoded in the dsr locus in th e oxidation of stored sulfur by phototrophic bacteria. The hupSL genes are uniformly present in the members of the Chromatiaceae family tested. The tw o genes between hydS and hydL encode a membrane-bound b-type cytochrome and a soluble iron-sulfur protein, respectively, resembling subunits of hetero disulfide reductase from methanogenic archaea. These genes are similar but not identical to dsrM and dsrK, indicating that the derived proteins have d istinct functions, the former in hydrogen metabolism and the latter in oxid ative sulfur metabolism. (C) 1999 Federation of European Microbiological So cieties. Published by Elsevier Science B.V. All rights reserved.