IDENTIFICATION AND CHARACTERIZATION OF A NEW BETA-GLUCOSIDE UTILIZATION SYSTEM IN BACILLUS-SUBTILIS

A new catabolic system in Bacillus subtilis involved in utilization of beta-glucosidic compounds has been investigated. It consists of five genes encoding phosphotransferase system (PTS) enzyme II (licB and lic C) and enzyme IIA (licA), a presumed 6-phospho-beta-glucosidase (licH) , as well as a putative regulator protein (licR). The genes map around 334 degrees of the B. subtilis chromosome, and their products are inv olved in the uptake and utilization of lichenan degradation products. These five genes are organized in two transcriptional units, A weak pr omoter precedes gene licR, and transcription is obviously terminated a t a secondary structure immediately downstream of the reading frame, a s shown by Northern RNA blot analysis. Genes licB, licC, licA, and lic H constitute an operon. Initiation of transcription at the promoter in front of this operon presumably requires activation by the gene produ ct of licR. The LicR protein shows an unusual domain structure, i.e., similarities to (i) the conserved transcriptional antiterminator BglG family signature and (ii) PTS enzyme II, Using RNA techniques and tran scriptional lacZ fusions, we have shown that the expression of the lic BCAH operon is inducible by products of lichenan hydrolysis, lichenan and cellobiose. The presence of excess glucose prevents the induction of this operon, indicating the control by carbon catabolite repression . Moreover, the expression of the operon requires the general PTS comp onents and seems to be negatively controlled by the specific lic PTS e nzymes.