Inactivation of Inhibits Biofilm Formation by Activating the Disulfide Stress Regulator Spx in Bacillus subtilis.

forms biofilms in response to internal and external stimuli. I previously showed that the deletion mutant was defective in biofilm formation, but the reason for this remains unidentified. CysL is a transcriptional activator of the operon, which encodes sulfite reductase, an enzyme involved in cysteine biosynthesis. Decreased production of sulfite reductase led to biofilm formation defects in the Δ mutant. The Δ mutation was suppressed by disrupting operon genes, whose products function upstream of sulfite reductase in the cysteine biosynthesis pathway, indicating that defects in cysteine biosynthesis were not a direct cause for the defective biofilm formation observed in the Δ mutant. The gene encodes phosphoadenosine phosphosulfate reductase, which requires a reduced form of thioredoxin (TrxA) as an electron donor. High expression of inhibited biofilm formation in the Δ mutant but not in the wild-type strain. Northern blot analysis showed that transcription was induced in the Δ mutant in a disulfide stress-induced regulator Spx-dependent manner. On the basis of these results, I propose that the Δ mutation causes phosphoadenosine phosphosulfate reductase to consume large amounts of reduced thioredoxin, inducing disulfide stress and activating Spx. The mutation restored biofilm formation to the Δ mutant. The Δ mutation reduced expression of the operon, which is required for exopolysaccharide production. Moreover, overexpression of the operon restored biofilm formation to the Δ mutant. Taken together, these results suggest that the Δ mutation activates Spx, which then inhibits biofilm formation through repression of the operon. has been studied as a model organism for biofilm formation. In this study, I explored why the deletion mutant was defective in biofilm formation. I demonstrated that the Δ mutation activated the disulfide stress response regulator Spx, which inhibits biofilm formation by repressing biofilm matrix genes. Homologs of Spx are highly conserved among Gram-positive bacteria with low G+C contents. In some pathogens, Spx is also reported to inhibit biofilm formation by repressing biofilm matrix genes, even though these genes and their regulation are quite different from those of Thus, the negative regulation of biofilm formation by Spx is likely to be well conserved across species and may be an appropriate target for control of biofilm formation.