Inorganic sulfur metabolism ensures the supply of electrons for the photoautotrophic growth of Rhodopseudomonas palustris.

The purple non sulfur bacterium Rhodopseudomonas palustris CGA009 grows photoautotrophically using light for ATP production and thiosulfate as an electron donor to fix CO2 into organic compounds, making it a promising chassis for value added product synthesis. To optimize thiosulfate utilization in metabolic engineering, understanding the regulation of thiosulfate oxidation is critical. Here, we cloned the sox genes cluster, which encodes the Sox multienzyme complex responsible for thiosulfate oxidation, and investigated its regulation by the ArsR family transcriptional regulator SoxR. We found that SoxR represses transcription of sox structural genes by binding to two specific DNA sequences: one in the soxY soxA intergenic region and another in the soxV promoter region. Mutations at residues R45 and S74 in SoxR abolished this DNA binding ability. Additionally, we identified tetrathionate as a novel electron donor supporting phototrophic growth of R. palustris. Through construction of sox genes mutants, we demonstrated that the sox genes cluster is essential for both thiosulfate and tetrathionate metabolism. These findings clarify the regulatory and metabolic mechanisms of inorganic sulfur compounds in R. palustris, providing insights into electron supply for photoautotrophic CO2 fixation.