Elucidating the mechanism of thiosulfate oxidation by a novel two-component system SulRS in deep-sea Campylobacterota

Members of the phylum <i>Campylobacterota</i>, which dominate deep-sea hydrothermal vent ecosystems, typically harbor the ability for thiosulfate oxidation through a complete sulfur oxidation (Sox) system encoded by the <i>soxABXY</i> _<i>1</i> <i>Z</i> _<i>1</i> and <i>soxCDY</i> _<i>2</i> <i>Z</i> _<i>2</i> gene clusters. Bioinformatic analysis identified a two-component regulatory system (TCS) SulRS in <i>Sulfurimonas hydrogeniphila</i>, a representative member of <i>Campylobacterota</i>. EMSA and DNase Ⅰ footprinting assays confirmed that SulR specifically binds to promoters P_x, P_y, and P_r, and its P_x-binding sequence contains two conserved direct repeat sequences. Combined microscale thermophoresis (MST) and dual-plasmid reporter assays showed that SulS can senses thiosulfate signals and activates <i>soxABXY</i> _<i>1</i> <i>Z</i> _<i>1</i> transcription, whereas this substrate exerts no significant effect on <i>soxCDY</i> _<i>2</i> <i>Z</i> _<i>2</i> transcription. Genomic analysis further revealed that <i>sulRS</i>-<i>soxABXY</i> _<i>1</i> <i>Z</i> _<i>1</i> -like gene clusters are widely conserved among sulfur-oxidizing bacteria within <i>Campylobacterota</i>. These findings suggest that the SulRS may play a pivotal role in regulating sulfur oxidation, likely facilitating the response, adaptation, and survival of these bacteria in chemosynthetic environments rich in reduced sulfur compounds.