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 monothiol bacilliredoxin, which debacillithiolates (removes BSH) the S-bacillithiolated glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) GapA and GapB in vivo and probably a number of other oxidized cytosolic proteins. Debacillithiolates the S-bacillithiolated Bdr (Bdr-SSB) and BrxB (BrxB-SSB) in vitro. Involved in maintaining redox homeostasis in response to disulfide stress conditions. Interacts with AbrB, BdhA, Bdr, BrxB, FolD, GapA, GapB, GatA, PfkA, PyrAA, PyrAB, PyrE, PyrG, PyrH, RpsB, RpsK, RpsL, SalA, SucC, Tuf and YtsJ. 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. Cells lacking the operon including this gene (ytxGH-brxC) have increased S-bacillithiolation of glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) GapA and GapB in cells with increased basal levels of oxidative stress due to concomitant deletion of genes encoding for catalase (katA) and alkyl hydroperoxide reductase (ahpCF).