Characterisation of the bacteriocins produced by two probiotic Lactobacillus isolates from idli batter

Lactobacillus plantarum JJ18 and Lactobacillus plantarum subsp. plantarum JJ60, probiotics from idli batter, produce bacteriocins JJ18 and JJ60 having a wide spectrum of activity. After optimising the environmental conditions for bacteriocin production the effect of various media components was determined. Maximum bacteriocin production was observed in MRS broth, pH 6.4 at 37 °C after 36 h. Tryptone (as nitrogen source) and glucose (as carbon source) are required for optimal production of bacteriocins JJ18 and JJ60. Activity was not affected by surfactants like Triton X-100, Tween 80 and Tween 20 or by treatment with NaCl, urea and EDTA. Protease treatment resulted in complete loss of activity of the partially purified bacteriocins JJ18 and JJ60, while lipase and α-amylase had no effect, indicating that the bacteriocin is a simple protein. Tris tricine SDS-PAGE electrophoresis depicted a single band of less than 3.5 kDa. However, the strain Lactobacillus plantarum JJ18 was inhibited by bacteriocin JJ60 and Lactobacillus plantarum JJ60 by bacteriocin JJ18, whereas no inhibition was observed against the respective producer strains, indicating that the two bacteriocins are different. The bacteriocins remained active over a wide range of pH and temperature. The bacteriocins were able to adsorb onto producer and target cells, Lactobacillus plantarum and Listeria monocytogenes and differentially in the presence of various surfactants, salts and solvents. A bactericidal mode of action was observed against Listeria monocytogenes. Given their wide spectrum of activity against various pathogens, the bacteriocins JJ18 and JJ60 can be applied as bio-preservatives in the food industry.