TRANSCRIPTIONAL ANALYSIS AND REGULATION OF CARNOBACTERIOCIN PRODUCTION IN CARNOBACTERIUM-PISCICOLA LV17

Bacteriocin production by Carnobacterium piscicola LV17 (carnobacterio cin, Cbn) depends on the level of inoculation when grown in liquid med ium. With an inoculum of greater than or equal to 10(6) colony-forming units per mi (cfu/ml), bacteriocin production is observed during expo nential growth, whereas with less than or equal to 10(4) cfu/ml no bac teriocin is detected even when the culture has reached stationary phas e. Using pure bacteriocins, it was demonstrated that bacteriocin produ ction is autoregulated. To understand how bacteriocin production is re gulated at the molecular level, cell-free supernatant from a bacterioc in-producing culture was added to fresh medium at 1% (v/v) together wi th a non-producing inoculum (10(4) cfu/ml), to induce bacteriocin prod uction (induced culture). Northern analysis revealed major transcripts of 0.35, 1.5 and 1 kb for carnobacteriocins A, B2 and BM1, respective ly, indicating that regulation of bacteriocin production by inoculum s ize occurs at the transcriptional level. Primer extension demonstrated that transcription initiated from the same promoters with the induced culture as with the positive control (culture inoculated at 10(7) cfu /ml). Quantitative phosphorimager analysis of the primer extension pro ducts indicated that cbnA transcript was more abundant than cbnB2 or c bnBM1. (C) 1997 Elsevier Science B.V.