Effect of Growth Medium on Bacteriocin Production by Lactobacillus plantarum ST194BZ, a Strain Isolated from Boza

Svetoslav Dimitrov Todorov and Leon Milner Theodore Dicks*

Department of Microbiology, University of Stellenbosch, 7600 Stellenbosch, South Africa

Article history:
Received August 3, 2004
Accepted February 28, 2005

Key words:
bacteriocin ST194BZ, Lactobacillus plantarum, boza

Summary:
The cell-free supernatant containing bacteriocin ST194BZ, produced by Lactobacillus plantarum ST194BZ, inhibits the growth of Lactobacillus casei, Lactobacillus sakei, Lactobacillus delbrueckii subsp. bulgaricus, Enterococcus faecalis, Escherichia coli, Enterobacter cloacae and Pseudomonas aeruginosa. Strain ST194BZ produces two bacteriocins, viz. ST194BZ(a) of 3.3 kDa and ST194BZ(b) of 14.0 kDa, based on tricine-SDS-PAGE. Reduction in bacteriocin activity was observed after treatment with proteinase K, trypsin and pronase, but not with catalase and α-amylase. A maximum total bacteriocin activity of 12 800 AU/mL was recorded after 14 h in MRS broth. In MRS broth adjusted to pH=5.5, 6.0 or 6.5, an equal level of bacteriocin production of 12 800 AU/mL was recorded. Optimal production (12 800 AU/ mL) was recorded in the presence of tryptone (20 g/L), a combination of tryptone and meat extract (1:0.6), or tryptone and yeast extract (1:0.6). Growth of strain ST194BZ in the presence of 10 or 20 g/L of D-mannose yielded bacteriocin levels of 12 800 AU/mL. In the presence of 30 or 40 g/L of mannose the activity levels doubled to 25 600 AU/mL. No difference in antibacterial activity was recorded when strain ST194BZ was grown in the presence of 2 g/L of K₂HPO₄ and 2 g/L of KH₂PO₄. Concentrations of 10, 20 and 50 g/L of KH₂PO₄ yielded double activity (25 600 AU/mL). Supplementing MRS with 1 g/L or more glycerol inhibited the production of bacteriocin. Growth in the presence of vitamins did not stimulate bacteriocin production. No plasmids were recorded for strain ST194BZ, suggesting that the genes encoding bacteriocin production are located on the genome.

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