The role of environmental factors and medium composition on bacteriocin production by an aquaculture probiotic Enterococcus faecium MC13 isolated from fish intestine

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The aim of this study was to optimize medium composition for higher yield of total viable cells and bacteriocin by Enterococcus faecium MC13. The factors such as peptone, meat extract, yeast extract, lactose, glycerol, tween 80, triammonium citrate and K2HPO4 were selected based on the Lactobacillus MRS medium composition. Two level factorial designs (FD) and steepest ascent path were performed to identify vital factors among the variables. Through the 2−8 FD, peptone, yeast extract and lactose were found to be significant factors involved in the enhanced production of viable cells and bacteriocin. Therefore, these three foremost factors were further optimized by central composite design to achieve efficient yield. The optimum MRS composition was found to be peptone (40.0 g/L), meat extract (30.0 g/L), yeast extract (40.0 g/L), lactose (24.0 g/L), glycerol (5.8 g/L), Tween 80 (3.0 g/L), triammonium citrate (1.0 g/L), K2HPO4 (2.5 g/L), MgSO4·7H2O (0.10 g/L), MnSO4·7H2O (0.05 g/L) and dipotassium PO4 (2.0 g/L). The optimized growth medium allowed higher amount of bacteriocin activity (36,100 AUml−1) and total viable cells (14.22 LogCFUml−1) production which were two-times higher than the commercial MRS medium.