A genomic view on syntrophic versus non-syntrophic lifestyle of anaerobic fatty acid-degrading bacteria

Abstract

of the earliest energy metabolism in the early Earth. However, many questions remain about how energy is conserved in sulfur-metabolizing organisms. A key reaction in microbial sulfur metabolism is the reduction of sulfite by the siroheme-containing dissimilatory sulfite reductase, DsrAB. This enzyme is present in sulfate, thiosulfate and sulfite reducing organisms, and also in sulfur-oxidizers where it is thought to operate in reverse. The mechanism of sulfite reduction by DsrAB has long been the subject of controversy due to the in vitro formation of thiosulfate and trithionate, in contrast to the closelyrelated assimilatory enzyme that produces only sulfide. Recent studies have identified the small protein DsrC [1] and the DsrMKJOPmembrane complex as physiological partners of DsrAB [2]. In particular, a crystal structure of DsrAB in complex with DsrC suggested the direct involvement of the latter protein in sulfite reduction and led to the proposal of a new mechanism for this reaction [3]. I will present recent in vivo and in vitro studies that reveal the function of DsrC in sulfite reduction, identifying the mechanism and physiological product of this reaction. These results implicate the respiratory membrane complex DsrMKJOP in the process, providing a direct link to energy conservation.