Optimization of bacteriocin production by Lactobacillus acidophilus AA11, a strain isolated from Egyptian cheese

The aim of this work was to investigate the effect of growth conditions on the maximum activity of bacteriocin production by Lactobacillus acidophilus AA11. The bacteriocin was produced at maximum activity in M17 broth supplemented with 0.5% lactose (M17L). The maximum growth of Lactobacillus acidophilus AA11 was obtained at 37 degrees C, while the optimal temperature for the bacteriocin production was 30 degrees C. The pH of bacterial culture also affected bacteriocin production. The optimal pH for bacterial growth and bacteriocin production was 6.5. Moreover, carbon and nitrogen sources significantly influenced the production of bacteriocin. The bacteriocin yield was at least 4-fold higher in M17 broth supplemented with lactose compared to other carbon sources. The optimal organic nitrogen source for bacteriocin production was yeast extract (4%). The addition of KH2PO4, CaCl2 or NH4PO4 into the medium resulted in significant suppression of bacteriocin; however, incorporation of MnSO4 resulted in an impressive increase in bacteriocin production. No increase in bacteriocin production was recorded in medium supplemented with vitamins. The addition of glycerol to the growth medium decreased bacteriocin production. Consequently, maximum bacteriocin activity was obtained in M17L medium (pH 6.5) supplemented with 4% yeast extract and MnSO4 at 30 degrees C. This optimization of bacteriocin production by modification of environmental growth conditions will greatly benefit efficient commercial application.