Characterization of leucocin B-KM432Bz from Leuconostoc pseudomesenteroides isolated from boza, and comparison of its efficiency to pediocin PA-1.

A bacteriocin-producing bacterium was isolated from boza and identified as Leuconostoc pseudomesenteroides KM432Bz. The antimicrobial peptide was purified and shown to be identical to other class IIa bacteriocins: leucocin A from Leuconostoc gelidum UAL-187 and Leuconostoc pseudomesenteroides QU15 and leucocin B from Leuconostoc carnosum Ta11a. The bacteriocin was named leucocin B-KM432Bz. Leucocin B-KM432Bz gene cluster encodes the bacteriocin precursor (lcnB), the immunity protein (lcnI) and the dedicated export machinery (lcnD and lcnE). A gene of unknown and non-essential function (lcnC), which is interrupted by an insertion sequence of the IS30 family, is localized between lcnB and lcnD. The activity of leucocin B-KM432Bz requires subunit C of the EII(t) Man mannose permease, which is the receptor for entry into target cells. The determination of the minimum inhibitory concentrations revealed the lowest values for leucocin B-KM432Bz over Listeria strains, with 4 to 32 fold better efficiency than pediocin PA-1.

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

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 alpha-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 degrees 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 KH(2)PO(4), or glycerol at 0.2% (w/v) suppressed bacteriocin production.