Advancing the Resolution of the Sulfur Compound Disproportionation Puzzle in Dissulfuribacter Thermophilus S69ᵀ Through Quantitative Label-Free Comparative Proteomics.

In deep-sea hydrothermal vents, sulfur compounds are central for microbial bioenergetics. Despite its significant impact on the global sulfur cycle, anaerobic sulfur compound disproportionation remains the least understood metabolism, with only three bacterial strains having been investigated at the proteomic level for their sulfur disproportionation metabolism to date. Here, we present a comparative proteomics study of the chemolithoautotrophic sulfur-cycling species Dissulfuribacter thermophilus S69ᵀ. Upon thiosulfate disproportionation conditions, proteomics revealed a high abundance of a cytoplasmic thiosulfate reductase AB homologue (PhsAB-like) that might reductively cleave thiosulfate into sulfide and sulfite. Subsequent steps might involve enzymes from the dissimilatory sulfate reduction, with Apr and Sat potentially functioning in reverse to produce sulfate. Strain S69T exhibited enhanced growth under sulfite/dihydrogen, likely due to both sulfite respiration and disproportionation. Here, a range of new enzymes were more abundant. These included an enzyme containing NrfD, the MolyAB as well as two membranous tetrathionate reductase homologues. Other membranous oxidoreductases such as QmoABC, DsrMKJOP and Complex I, may contribute to the pathway, while autotrophic growth is likely sustained by the Wood-Ljungdahl pathway. These findings highlight the distinct enzymatic features of strain S69ᵀ compared to previously proteomically characterised sulfur-disproportionating strains, revealing novel enzymes that warrant further analysis.