Influence of growth conditions on the production of a bacteriocin by Lactococcus lactis subsp. lactis ST34BR, a strain isolated from barley beer.

Abstract

Bacteriocin ST34BR, a small polypeptide of 2.9 kDa produced by Lactococcus lactis subsp. lactis ST34BR, inhibits the growth of Enterococcus faecalis, Escherichia coli, Lactobacillus plantarum, Lactobacillus casei, Pseudomonas aeruginosa and Staphylococcus aureus. MRS broth, adjusted to pH 6.0 yielded 6,400 AU/ml, compared to 400 AU/ml recorded in BHI broth, M17 broth, 10% (w/v) soy milk, and 8% and 10% (w/v) molasses. At pH of 4.5 only 800 AU/ml was produced. Based on comparative studies in MRS broth, without organic nitrogen, supplemented with different combinations of tryptone, meat extract and yeast extract, tryptone was identified as the stimulating nitrogen compound. Growth in the presence of 20 g/l glucose, maltose, mannose or sucrose yielded bacteriocin levels of 6,400 AU/ml, whereas the same concentration of lactose and fructose yielded 3,200 AU/ml and 1,600 AU/ml, respectively. No difference in bacteriocin ST34BR activity was recorded in MRS broth supplemented with 2 g/l K2HPO4 and 2 g/l, 5 g/l, 10 g/l or 50 g/l KH2PO4. However, 20 g/l KH2PO4 increased bacteriocin ST34BR production to 12,800 AU/ml. Glycerol at 1g/l to 10 g/l in MRS broth reduced bacteriocin activity to 3,200 AU/ml, whilst 20 g/l and 50 g/l yielded only 1,600 AU/ml. The presence of cyanocobalamin, L-ascorbic acid, thiamine and DL-6,8-thioctic acid in MRS broth at 1.0 ppm, respectively, did not result in increased activity levels.