Genetic Potential of Dissulfurimicrobium hydrothermale, an Obligate Sulfur-Disproportionating Thermophilic Microorganism

The biochemical pathways of anaerobic sulfur disproportionation are only partially deciphered, and the mechanisms involved in the first step of S(0)-disproportionation remain unknown. Here, we present the results of sequencing and analysis of the complete genome of Dissulfurimicrobium hydrothermale strain Sh68(T), one of two strains isolated to date known to grow exclusively by anaerobic disproportionation of inorganic sulfur compounds. Dissulfurimicrobium hydrothermale Sh68(T) is a motile, thermophilic, anaerobic, chemolithoautotrophic microorganism isolated from a hydrothermal pond at Uzon caldera, Kamchatka, Russia. It is able to produce energy and grow by disproportionation of elemental sulfur, sulfite and thiosulfate. Its genome consists of a circular chromosome of 2,025,450 base pairs, has a G + C content of 49.66% and a completion of 97.6%. Genomic data suggest that CO(2) assimilation is carried out by the Wood–Ljungdhal pathway and that central anabolism involves the gluconeogenesis pathway. The genome of strain Sh68(T) encodes the complete gene set of the dissimilatory sulfate reduction pathway, some of which are likely to be involved in sulfur disproportionation. A short sequence protein of unknown function present in the genome of strain Sh68(T) is conserved in the genomes of a large panel of other S(0)-disproportionating bacteria and was absent from the genomes of microorganisms incapable of elemental sulfur disproportionation. We propose that this protein may be involved in the first step of elemental sulfur disproportionation, as S(0) is poorly soluble and unable to cross the cytoplasmic membrane in this form.