REGULATION OF THE BACILLUS-SUBTILIS ALSS, ALSD, AND ALSR GENES INVOLVED IN POST-EXPONENTIAL-PHASE PRODUCTION OF ACETOIN

Acetoin is a major extracellular product of Bacillus subtilis grown on glucose and other fermentable carbon sources. The enzymes responsible for the formation of acetoin, acetolactate synthase, and acetolactate decarboxylase are synthesized in detectable amounts only in cells tha t have reached stationary phase. We have cloned and sequenced the gene s encoding these enzymes, alsS and alsD, as well as a gene, alsR, that regulates their expression. alsS and alsD appear to compose a single operon, while alsR is transcribed divergently from the alsSD operon. A lsR shows significant homology to the LysR family of bacterial activat or proteins, and when alsR is disrupted the alsSD operon is not expres sed. Transcriptional fusions to alsS and alsR revealed that AlsR is re quired for the transcription of the alsSD operon, which increases duri ng stationary phase. Two mutations that cause increased expression of the alsSD operon have been isolated, cloned, and sequenced. They each change an amino acid in the AlsR protein.