Figure 4.
Pathways for bacterial sulfur transformation in the periplasm. Oxidation of S2− and S0: Flavocyt c sulfide dehydrogenases (FCSDs) can oxidize H2S to the final product polysulfide. In dissimilatory sulfur-oxidizing bacteria, Rhds and PDOs are located in the periplasm, and the oxidation of H2S is catalyzed by SQRs, which consistently expose the reaction to the periplasm space. Oxidation of S0 and S2+: Unconjugated SoxYZ is catalyzed by SoxAX with S2O32−, generating SoxYZ-S-S-SO3−, which is subsequently converted to SoxYZ-S-S−, releasing one molecular of SO42− under the catalysis of SoxB. Reduction of S2+: TtrABC and TsdAB are responsible for interconversion of S4O62− and S2O32−. Reduction of S0: PhsABC and PsrABC are supposed to participate in the reduction of S0 (Sn2−) and S0 (S2O32−) to HS−.