Diversity of Sulfur-Disproportionating Microorganisms

Microorganisms disproportionating inorganic sulfur compounds are involved in biogeochemical cycles of elements in the modern biosphere. Sulfur-disproportionating prokaryotes are represented by 30 species of the Bacteria domain and belong to the phyla Proteobacteria, Thermodesulfobacteria, and Firmicutes. Most of the sulfur-disproportionating bacteria belong to four orders of the class Deltaproteobacteria. The microorganisms responsible for dismutation of sulfur compounds inhabit freshwater and shallow marine sediments, hypersaline and soda lakes, anthropogenic environments, and various natural thermal ecosystems. Most sulfur-disproportionating organisms are able to use other processes for growth, primarily dissimilatory sulfate reduction. Ability to grow autotrophically was shown for 17 sulfur-disproportionating strains from different phylogenetic groups. The biochemical mechanisms involved in disproportionation of sulfur compounds remain uncertain, which hinders the application of the current omics techniques. Comparative analysis of available complete genomes of the microorganisms capable of elemental sulfur disproportionation is provided. The presence of the complete set of the dissimilatory sulfate reduction genes was found not to be necessary for S-0 disproportionation. This process does not require dissimilatory sulfite reductase (Dsr) and adenylyl-sulfate reductase (Apr). Sulfur relay proteins and the elemental sulfur- and/or polysulfides-reducing enzymes are important in sulfur disproportionation, but different microorganisms probably employ different sulfur transferases and polysulfide reductases in these processes.