CHARACTERIZATION OF A LOCUS FROM CARNOBACTERIUM-PISCICOLA LV17B INVOLVED IN BACTERIOCIN PRODUCTION AND IMMUNITY - EVIDENCE FOR GLOBAL INDUCER-MEDIATED TRANSCRIPTIONAL REGULATION

Mutational, nucleotide sequence, and transcriptional analyses of a 10- kb fragment (carnobacteriocin locus) from the 61-kb plasmid of Carnoba cterium piscicola LV17B demonstrated the presence of two gene clusters (cbnXY and cbnSKRTD) upstream of the previously sequenced carnobacter iocin B2 structural and immunity genes (cbnB2 and cbiB2), Deduced prod ucts of cbnK and cbnR have sequence similarity to proteins of Agr-type two-component signal transduction systems, and those of cbnT and cbnD have sequence similarity to proteins of signal sequence-independent s ecretion systems, Deduced products of cbnX, cbnY, and cbnS are class I I-type bacteriocin precursors,vith potential leader peptides containin g double-glycine cleavage sites, Genetic analysis indicated that the 1 0-kb locus contains information required for the production of, and im munity to, the plasmid-encoded carnobacteriocin B2 and the chromosomal ly encoded carnobacteriocin BM1, In addition, this locus is involved i n the production of at least one additional antimicrobial compound and an inducer factor that plays a role in the regulation of carnobacteri ocin B2, Transcription analysis indicated that the operons cbnXY, cbnB 2-cbiB2, and cbnBM1-cbiBM1 (with the latter encoding carnobacteriocin BM1 and its immunity protein on the chromosome) and two small transcri pts containing cbnS are transcribed only in induced cultures, These tr anscripts are coregulated and subject to inducer-mediated transcriptio nal control, Similar regulation of the cbn operons is mirrored by the similarity in the nucleotide sequence of their promoter regions, all o f which contain two imperfect direct repeats resembling those in Agr-l ike regulated promoters upstream of the transcription start sites.