ELEMENTAL SULFUR AND THIOSULFATE DISPROPORTIONATION BY DESULFOCAPSA SULFOEXIGENS SP-NOV, A NEW ANAEROBIC BACTERIUM ISOLATED FROM MARINE SURFACE SEDIMENT

A mesophilic, anaerobic, gram-negative bacterium, strain SB164P1, was enriched and isolated from oxidized marine surface sediment with eleme ntal sulfur as the sole energy substrate in the presence of ferrihydri te. Elemental sulfur was disproportionated to hydrogen sulfide and sul fate. Growth was observed exclusively in the presence of a hydrogen su lfide scavenger, e.g. ferrihydrite. In the absence of a scavenger, sul fide and sulfate production were observed but no growth occurred. Stra in SB164P1 grew also by disproportionation of thiosulfate and sulfite, With thiosulfate, the growth efficiency was higher in ferrihydrite su pplemented media than in media without ferrihydrite. Growth coupled to sulfate reduction was not observed. However, a slight sulfide product ion occurred in cultures incubated with formate and sulfate. Strain SB 164P1 is the first bacterium described that grows chemolithoautotrophi cally exclusively by the disproportionation of inorganic sulfur compou nds. Comparative 16S rDNA sequencing analysis placed strain SB164P1 in to the delta subclass of the class Proteobacteria. Its closest relativ e is Desulfocapsa thiozymogenes, and slightly more distantly related a re Desulfofustis glycolicus and Desulforhopalus vacuolatus. This phylo genetic cluster of organisms, together with members of the genus Desul fobulbus, forms one of the main lines of descent within the delta subc lass of the Proteobacteria. Due to the common phenotypic characteristi cs and the phylogenetic relatedness to Desulfocapsa thiozymogenes, we propose that strain SB164P1 be designated the type strain of Desulfoca psa sulfoexigens sp. nov.