Regulation of the acetoin catabolic pathway is controlled by sigma L in Bacillus subtilis

Bacillus subtilis grown in media containing amino acids or glucose secretes acetate, pyruvate, and large quantities of acetoin into the growth medium. Acetoin can be reused by the bacteria during stationary phase when other c arbon sources have been depleted, The acoABCL operon encodes the E1 alpha, E1 beta, E2, and E3 subunits of the acetoin dehydrogenase complex in B. sub tilis, Expression of this operon is induced by acetoin and repressed by glu cose in the growth medium, The acoR gene is located downstream from the aco ABCL operon and encodes a positive regulator which stimulates the transcrip tion of the operon, The product of acoR has similarities to transcriptional activators of sigma 54-dependent promoters. The four genes,of the operon a re transcribed from a -12, -24 promoter, and transcription is abolished in acoR and sigL mutants, Deletion analysis showed that DNA sequences more tha n 85 bp upstream from the transcriptional start site are necessary for full induction of the operon, These upstream activating sequences are probably the targets of AcoR, Analysis of an acoR'-'lacZ strain of B. subtilis showe d that the expression of acoR is not induced by acetoin and is repressed by the presence of glucose in the growth medium, Transcription of acoR is als o negatively controlled by CcpA, a global regulator of carbon catabolite re pression. A specific interaction of CcpA in the upstream region of acoR was demonstrated by DNase I footprinting experiments, suggesting that repressi on of transcription of acoR is mediated by the binding of CcpA to the promo ter region of acoR.