Influence of the σ ^B Stress Factor and yxaB , the Gene for a Putative Exopolysaccharide Synthase under σ ^B Control, on Biofilm Formation

Bacillus subtilis forms structured communities of biofilms encased in an exopolysaccharide matrix on solid surfaces and at the air-liquid interface. It is postulated that nonoptimal growth conditions induce this multicellular behavior. We showed that under laboratory conditions a strain deleted for sigB was unable to form a floating pellicle on the surface of a liquid medium. However, overexpression of yxaB , encoding a putative exopolysaccharide synthase, from a p Spac promoter in a sigB -deleted strain resulted in partial recovery of the wild-type phenotype, indicating the participation of the YxaB protein in this multicellular process. We present data concerning the regulation of transcription of genes yxaB and yxaA , encoding a putative glycerate kinase. Both genes are cotranscribed as a single transcription unit from a σ A -dependent promoter during vegetative growth of a liquid bacterial culture. The promoter driving transcription of the yxaAB operon is regulated by AbrB. In addition, the second gene in the operon, yxaB , possesses its own promoter, which is recognized by RNA polymerase containing the σ B subunit. This transcription start site is used under general stress conditions, resulting in increased expression.