Partial characterisation of two bacteriocins produced byLactobacillus paracasei subsp.paracasei ST242BZ and ST284BZ and the effect of medium components on their production

The influence of medium components on production of bacteriocins ST242BZ (10.0 kDa) and ST284BZ (3.5 kDa) byLactobacillus paracasei subsp.paracasei ST242BZ and ST284BZ have been studied. Growth in MRS broth (pH of 6.5) yielded bacteriocin levels of 12800 AU/ml. Modified MRS with tryptone as the only nitrogen source, MRS supplemented with KH₂PO₄ (10–100 g/l), or MRS supplemented with thiamine increased bacteriocin ST242BZ production to 25600 AU/ml. Tryptone, combinations of tryptone, meat extract and yeast extract, or thiamine did not increase bacteriocin ST284BZ production. However, MRS supplemented with K₂HPO₄ (50–100 g/l) increased bacteriocin ST284BZ production up to 25600 AU/ml. Our results suggest that production of bacteriocins ST242BZ and ST284BZ are stimulated by potassium ions.