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

Abstract

Bacillus subtilis forms biofilms in response to internal and external stimuli. I previously showed that the cysL deletion mutant was defective in biofilm formation, but the reason for this remains unidentified. CysL is a transcriptional activator of the cysJI operon, which encodes sulfite reductase, an enzyme involved in cysteine biosynthesis. Decreased production of sulfite reductase led to biofilm formation defects in the ΔcysL mutant. The ΔcysL mutation was suppressed by disrupting cysH 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 ΔcysL mutant. The cysH gene encodes phosphoadenosine phosphosulfate reductase, which requires a reduced form of thioredoxin (TrxA) as an electron donor. High expression of trxA inhibited biofilm formation in the ΔcysL mutant but not in the wild-type strain. Northern blot analysis showed that trxA transcription was induced in the ΔcysL mutant in a disulfide stress-induced regulator Spx-dependent manner. On the basis of these results, I propose that the ΔcysL mutation causes phosphoadenosine phosphosulfate reductase to consume large amounts of reduced thioredoxin, inducing disulfide stress and activating Spx. The spx mutation restored biofilm formation to the ΔcysL mutant. The ΔcysL mutation reduced expression of the eps operon, which is required for exopolysaccharide production. Moreover, overexpression of the eps operon restored biofilm formation to the ΔcysL mutant. Taken together, these results suggest that the ΔcysL mutation activates Spx, which then inhibits biofilm formation through repression of the eps operon.

Cellular redox state affects biofilm formation by a surfactin -dependent manner in Bacillus amyloliquefaciens?

“…Spx has been reported to inhibit biofilm formation [30], and inactivation of spx can enhance the biofilm formation in B. subtilis [31]. However, Δspx showed a colony morphology and biofilm with less wrinkles but could be partially restored by compensation of spx , indicating that spx plays a positive role in the biofilm formation here.…”

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“…Spx has been reported to inhibit biofilm formation [33], and inactivation of spx can enhance the biofilm formation in B. subtilis [34]. However, Δ spx showed a colony morphology and biofilm with less wrinkles but could be partially restored by compensation of spx , indicating that spx plays a positive role in the biofilm formation here.…”

Carboxy-Terminal Processing Protease Controls Production of Outer Membrane Vesicles and Biofilm in Acinetobacter baumannii

“…Several studies have reported that increased CPS content contributes to increased biofilm formation [ 52 , 53 ]. The quantitative analysis of the biofilm’s CV staining revealed that significantly more biofilm adhered to the glass surface in MR14 compared with ATCC 17978 and MR14C ( Figure 3 ).…”