Optimization of Fermentation Conditions of Bacillus thuringiensis EC1 for Enhanced Methionine Production

摘要

Bacillus thuringiensis EC1, isolated from the fermented oil bean seed, Pentachletra macrophila Benthan, produced a methionine yield of 1.89 mg/ml. The influence of cultural conditions on methionine accumulation by B. thuringiensis EC1 showed that a 20% medium/fermenter volume ratio and a 5% inoculum size increased methionine yield. The carbon of choice was maltose and at 8% level stimulated methionine production. Among the nitrogen sources studied, ammonium sulphate was found to be the best and at 1% concentration produced a methionine yield of 2.56 mg/ml. All growth-promoting substances and their mixtures enhanced methionine accumulation by B. thuringiensis EC1. The effect of Vitamins on methionine production showed that riboflavin and thiamine HCl at 1.0 μg/ml yielded 2.49 mg/ml and 2.80 mg/ml methionine respectively. The influence of bivalent metals on methionine accumulation indicated that Zn2+ at all concentration stimulated methionine production. Mg2+ and Ba2+ at 0.1 μg/ml and 10.0 μg/ml respectively improved methionine yield. Optimizing the cultural conditions of B. thuringiensis EC1 in submerged medium gave a methionine yield of 3.18 mg/ml.