Genome-based taxonomic classification of the genus Sulfitobacter along with the proposal of a new genus Parasulfitobacter gen. nov. and exploring the gene clusters associated with sulfur oxidation.

BACKGROUND: The genus Sulfitobacter, a member of the family Roseobacteraceae, is widely distributed in the ocean and is believed to play crucial roles in the global sulfur cycle. However, gene clusters associated with sulfur oxidation in genomes of the type strains of this genus have been poorly studied. Furthermore, taxonomic errors have been identified in this genus, potentially leading to significant confusion in ecological and evolutionary interpretations in subsequent studies of the genus Sulfitobacter. This study aims to investigate the taxonomic status of this genus and explore the metabolism associated with sulfur oxidation.

RESULTS: This study suggests that Sulfitobacter algicola does not belong to Sulfitobacter and should be reclassified into a novel genus, for which we propose the name Parasulfitobacter gen. nov., with Parasulfitobacter algicola comb. nov. as the type species. Additionally, enzymes involved in the sulfur oxidation process, such as the sulfur oxidization (Sox) system, the disulfide reductase protein family, and the sulfite dehydrogenase (SoeABC), were identified in almost all Sulfitobacter species. This finding implies that the majority of Sulfitobacter species can oxidize reduced sulfur compounds. Differences in the modular organization of sox gene clusters among Sulfitobacter species were identified, along with the presence of five genes with unknown function located in some of the sox gene clusters. Lastly, this study revealed the presence of the demethylation pathway and the cleavage pathway used by many Sulfitobacter species to degrade dimethylsulfoniopropionate (DMSP). These pathways enable these bacteria to utilize DMSP as important source of sulfur and carbon or as a defence strategy.

CONCLUSIONS: Our findings contribute to interpreting the mechanism by which Sulfitobacter species participate in the global sulfur cycle. The taxonomic rearrangement of S. algicola into the novel genus Parasulfitobacter will prevent confusion in ecological and evolutionary interpretations in future studies of the genus Sulfitobacter.