Optimization of bacteriocin production by Lactobacillus plantarum ST13BR, a strain isolated from barley beer

Abstract

The cell-free supernatant containing bacteriocin ST13BR, produced by Lactobacillus plantarum ST13BR, inhibits the growth of L. casei, Pseudomonas aeruginosa, Enterococcus faecalis, Klebsiella pneumoniae and Escherichia coli. Based on tricine-SDS-PAGE, bacteriocin ST13BR is 10 kDa in size. Complete inactivation or significant reduction in bacteriocin activity was observed after treatment with Proteinase K, trypsin and pronase, but not with catalase or α-amylase. Low bacteriocin activity (200 AU/ml) was recorded in BHI medium, M17 broth, 10% (w/v) soy milk, and 2% and 10% (w/v) molasses, despite good growth. Maximal bacteriocin activity (6,400 AU/ml) was recorded after 23 h in MRS broth, but only at 30°C. Tween 80 in MRS broth increased bacteriocin production by more than 50%. Meat extract or yeast extract as sole nitrogen source, or a combination of the two (1 : 1) in MRS broth, stimulated bacteriocin production (6,400 AU/ml). Only 50% activity (3,200 AU/ml) was recorded with tryptone as sole nitrogen source, whereas a combination of tryptone, meat extract and yeast extract yielded 6,400 AU/ml. Bacteriocin production was not stimulated by the addition of glucose at 2.0% w/v (3,200 AU/ml), nor 2% (w/v) fructose, sucrose, lactose or mannose, respectively (800 AU/ml). Activity levels less than 200 AU/ml were recorded in the presence of 0.05% to 0.5% (w/v) maltose. Maximal bacteriocin production (6,400 AU/ml) was recorded in the presence of 2% (w/v) maltose. Maltose at 4.0% (w/v) led to a 50% reduction of bacteriocin activity. The presence of 1.0% (w/v) and higher KH2PO4, or glycerol at 0.2% (w/v) suppressed bacteriocin production.