Utilization of Various Starch Hydrolysates and Defatted Proteins by Bacillus cereus for Microbial Synthesis of Methionine in Submerged Medium

Abstract

Three of the methionine-producing bacteria previously isolated from different soil ecovars in Owerri, characterized as Bacillus cereus no: DS13, RS16 and AS9, based on 16s rRNA sequencing, were screened for utilization agricultural products for production of methionine. Experimental studies on the Bacillus strains were carried out to examine the use of various starch hydrolysates from different agricultural products: wheat, sorghum, cassava, cocoyam, yam, plantain, millet, corn, potato, rice and defatted plant proteins: pigeon pea, cowpea, bambaranut, groundnut and soybean meal as source of carbon and nitrogen, respectively for the production of methionine. The result of the influence of various carbon and nitrogen sources on methionine production showed that 2.32mg/ml methionine accumulation in the culture broth of B. cereus DS13 when corn-starch hydrolysate/defatted groundnut meal was used, while B. cereus RS16 and Bacillus cereus DS13 gave the same methionine yield of 2.22mg/ml with corn-starch hydrolysate/defatted groundnut meal and sorghum hydrolysate/soyabean meal respectively. Bacillus cereus AS9 utilized wheat starch hydrolysate/soaybean meal, followed by plaintain-starch hydrolysate/bambaranut to produced 1.79mg/ml and 1.78mg/ml methionine respectively. Methionine was accumulated in the fermentation broth of the Bacillus strains after a fermentation period of 96h. This study indicates the possible utilization of agricultural products as substrates for L-methionine production in submerged medium especially when considering the limitations of producing methionine by fermentation processes.