Two pathways for thiosulfate oxidation in the alphaproteobacterial chemolithotroph Paracoccus thiocyanatus SST

Publication date: Available online 23 September 2019Source: Microbiological ResearchAuthor(s): Moidu Jameela Rameez, Prosenjit Pyne, Subhrangshu Mandal, Sumit Chatterjee, Masrure Alam, Sabyasachi Bhattacharya, Nibendu Mondal, Jagannath Sarkar, Wriddhiman GhoshAbstractChemolithotrophic bacteria oxidize various sulfur species for energy and electrons, thereby operationalizing biogeochemical sulfur cycles in nature. The best-studied pathway of bacterial sulfur-chemolithotrophy involves direct oxidation of thiosulfate (S2O32-) to sulfate (SO42-) without any free intermediate. This pathway mediated by SoxXAYZBCD is apparently the exclusive mechanism of thiosulfate oxidation in facultatively chemolithotrophic alphaproteobacteria. Here we explore the molecular mechanisms of sulfur oxidation in the thiosulfate- and tetrathionate(S4O62-)-oxidizing alphaproteobacterium Paracoccus thiocyanatus SST, and compare them with the prototypical Sox process of Paracoccus pantotrophus. Our results reveal a unique case where an alphaproteobacterium has Sox as its secondary pathway of thiosulfate oxidation converting ˜10% of the thiosulfate supplied, whilst ˜90% of the substrate is oxidized via a pathway that produces tetrathionate as an intermediate. Sulfur oxidation kinetics of a deletion mutant showed that thiosulfate-to-tetrathionate conversion, in SST, is catalyzed by a thiosulfate dehydrogenase (TsdA) homolog that has far-higher substrate-affinity than the Sox system of this bacterium, whic...
Source: Microbiological Research - Category: Infectious Diseases Source Type: research