Production optimization and characterization of a low molecular weight bacteriocin from Lactococcus lactis subsp. lactis

Abstract

Lactococcus lactis subsp. lactis is very important as starter culture of cheese and yogurt production. A variety of bacteriocins ranging the molecular weight 3 to 10 have been reported from L. lactis under different growth conditions. In our study, we have optimized the growth of L. lactis for the bacteriocin production. Growth kinetics of these bacteria was studied in accordance to time, pH and temperature. Optimum growth as well as optimum bacteriocin activity was obtained after 18 h at pH 5.0 and temperature 37°C. Bacteriocin activity was produced on optimal conditions and were further characterized and purified. Antibacterial assay of bacteriocin showed the strong growth inhibition of test bacteria. Bacteriocin activities were checked after their treatment with different enzymes, organic solvents, sodium chloride (NaCl) and detergents as well as their heat stability and effect of pH was studied. Bacteriocin activity was found to heat stability at 100°C for 30 min and activity was found stable in the 3 to 10 pH range but lost the activity after the treatment with proteinase-K and protease enzymes. Urea, ethylenediaminetetraacetic acid (EDTA) and 6% affected the bacteriocin activity. Bactericidal activity was further purified to homogeneity by ammonium sulphate precipitation and chromatographic techniques. Molecular weight was calculated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as 4.6 kDa. Key words: Bacteriocin activity, Lactococcus lactis, growth kinetics, antibacterial assay.