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 dithiol bacilliredoxin, which debacillithiolates (removes BSH) the S-bacillithiolated OhrR (OhrR-SSB) in vitro and in vivo NaOCl-generated S-bacillithiolated MetE (MetE-SSB). Involved in maintaining redox homeostasis in response to disulfide stress conditions (PubMed:24313874). Has a redox potential of -130 mV. Displays weak protein disulfide isomerase activity in vitro (PubMed:19653655). Expression is up-regulated by cumene hydroperoxide (CHP). N-terminal Cys of the CXC active site motif 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. Mild sensitivity to cumene hydroperoxide (CHP) as indicated by growth inhibition assay. No effect on growth after NaOCl treatment. Belongs to the bacilliredoxin family.