Elemental sulfur and thiosulfate disproportionation by Desulfocapsa sulfoexigens sp. nov., a new anaerobic bacterium isolated from marine surface sediment

Abstract

A mesophilic, anaerobic, gram-negative bacterium, strain SB164P1, was enriched and isolated from oxidized marine surface sediment with elemental sulfur as the sole energy substrate in the presence of ferrihydrite. Elemental sulfur was disproportionated to hydrogen sulfide and sulfate. Growth was observed exclusively in the presence of a hydrogen sulfide scavenger, e.g., ferrihydrite. In the absence of a scavenger, sulfide and sulfate production were observed but no growth occurred. Strain SB164P1 grew also by disproportionation of thiosulfate and sulfite. With thiosulfate, the growth efficiency was higher in ferrihydrite-supplemented media than in media without ferrihydrite. Growth coupled to sulfate reduction was not observed. However, a slight sulfide production occurred in cultures incubated with formate and sulfate. Strain SB164P1 is the first bacterium described that grows chemolithoautotrophically exclusively by the disproportionation of inorganic sulfur compounds. Comparative 16S rDNA sequencing analysis placed strain SB164P1 into the delta subclass of the class Proteobacteria. Its closest relative is Desulfocapsa thiozymogenes, and slightly more distantly related are Desulfofustis glycolicus and Desulforhopalus vacuolatus. This phylogenetic cluster of organisms, together with members of the genus Desulfobulbus, forms one of the main lines of descent within the delta subclass of the Proteobacteria. Due to the common phenotypic characteristics and the phylogenetic relatedness to Desulfocapsa thiozymogenes, we propose that strain SB164P1 be designated the type strain of Desulfocapsa sulfoexigens sp. nov.

FIG. 1

Phase-contrast photomicrograph of D. sulfoexigens SB164P1 grown with elemental sulfur and ferrihydrite. Most ferrihydrite and iron sulfide precipitates were dissolved by dithionite-citrate-acetic acid extraction. Residual precipitates are seen as highly refractive aggregates. Bar, 10 μm.

FIG. 2

Thiosulfate metabolism of strain SB164P1. (Top) Incubation without ferrihydrite. Results are means of two incubations. (Middle) Incubation with ferrihydrite. Results are means of two incubations. (Bottom) Cell counts from two parallel incubations with and without ferrihydrite. Note the logarithmic scale.

FIG. 3

Elemental sulfur metabolism of strain SB164P1. Sulfur was added in excess. (Top) Incubation without ferrihydrite. Results are means of two incubations. (Middle) Incubation with ferrihydrite. Results are means of two incubations. FeS₂ represents pyrite sulfur. Note the different scales in the top and middle panels. (Bottom) Cell counts from two parallel incubations with and without ferrihydrite. Note the logarithmic scale.

FIG. 4

Phylogenetic tree based on 16S rRNA sequences showing the relationship between strain SB164P1 and its closest relatives as well as 62 other reference organisms of the delta subclass of the Proteobacteria. The triangles indicate groups of phylogenetically related species or genera: 1, Desulfobacter spp. plus Desulfobacterium, Desulfobacula, and Desulfosarcina spp.; 2, Syntrophobacter spp. plus Desulfoacinum and Desulforhabdus spp.; 3, Geobacter spp. plus Desulfuromonas, Desulfuromusa, and Pelobacter spp.; 4, Desulfovibrio spp. plus Desulfohalobium and Desulfomicrobium spp. The 16S rRNA sequence of E. coli was used as an outgroup reference. The scale bar represents the estimated number of base changes per nucleotide sequence position.