Medium components effecting bacteriocin production by two strains of Lactobacillus plantarum ST414BZ and ST664BZ isolated from boza

Bacteriocins ST414BZ and ST664BZ, produced by Lactobacillus plantarum, inhibited the growth of a number of lactic acid bacteria, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae and Enterobacter cloacae. Optimal production of bacteriocin ST664BZ (12 800 AU/mL) was recorded in MRS broth with an initial pH of 6.0 and 6.5. Bacteriocin ST414BZ was produced in MRS broth at lower pH values, ranging from 6.5 to 5.0. Low levels of bacteriocin activity were produced in BHI, M17, 10% (w/v) soy flour and 10% (w/v) molasses, suggesting that specific nutrients are required for optimal production. Bacteriocin ST414BZ production doubled (from 12 800 to 25 600 AU/mL) in MRS broth with tryptone as sole nitrogen source, or when glucose was replaced with maltose. Bacteriocin ST664BZ production, on the other hand, was less influenced by changes in nitrogen content, but increased two-fold (to 25 600 AU/mL) when glucose was replaced with sucrose, maltose or mannose, or when MRS broth was supplemented with 2.0 g/L KH₂ PO₄. Enrichment of MRS broth with vitamins B₁₂, B₁ or C did not stimulate production of the two bacteriocins. Growth in the presence of DL-6,8-thioctic acid increased bacteriocin ST664BZ production to 25 600 AU/mL. Concluded from these results, optimal levels of bacteriocins ST414BZ and ST664BZ will be produced in boza enriched with tryptone and maltose.