S-bacillithiolation is the formation of mixed disulfide bonds between protein thiols and the general thiol reductant bacillithiol (BSH) under oxidative stress. BSH is an equivalent of glutathione (GSH) in Firmicutes. This protein is a NADPH-dependent bacilliredoxin reductase, which debacillithiolates (removes BSH) the S-bacillithiolated BrxB (BrxB-SSB), and to a lesser extent BrxC (BrxC-SSB). Involved in a redox cascade increasing the efficacy of BrxB function by reducing BrxB-SSB and thus reactivating it. Has NADPH-dependent oxidase activity under aerobic conditions producing hydrogen peroxide (H(2)O(2)). Interacts with BrxC. C-terminal Cys can react with bacillithiol (BSH) to form mixed disulfides. S-bacillithiolation protects Cys residues against overoxidation by acting as a redox switch in response to oxidative stress.