Enhanced L-lysine Production by UV-irradiated and S-2-aminoethyl-L-cysteine Resistant Mutants Derived from Bacillus species Using Agricultural Products as Carbon and Nitrogen Sources

Abstract

L-Lysine is essential for human and animal nutrition and may be added to food and feed materials to improve the protein quality. It is utilized in human medicine, in cosmetics and in the pharmaceutical industry, particularly in the formulation of diets with balanced amino acid concentration and in amino acid infusions. Enhanced L-lysine production by UV irradiated and S-2-aminoethyl-L-cysteine resistant (AECR) mutants derived from Bacillus species, using agricultural products as carbon and nitrogen sources was studied. The L-lysine producing bacteria had already been isolated from Nigerian soil. They were purified and identified as B. subtilis PR13, B. subtilis PR9 and B. pumilus SS16, using cultural and biochemical characteristics. UV irradiated mutants were obtained by exposing the parent strains which include B. subtilis PR13, B. subtilis PR9 and B. pumilus SS16,  to UV light while, AECR mutants were derived by exposing the parent strains to various concentrations of AEC. The mutants were screened for L-lysine production by cultivating in fermentation media. The results obtained showed that, UV mutants PRMU-8 and PRMU-14 derived from Bacillus subtilis PR13 accumulated higher lysine yield of 2.47 and 2.55 mg/ml compared to the wild type. Also, UV mutant MUPR-4 derived from Bacillus subtilis PR9 recorded a higher lysine yield of 1.77 mg/ml while, enhanced lysine yields of 1.96 and 2.34 mg/ml were observed in UV mutants SSMU-4 and SSMU-9 respectively. AECR mutant PRT-2 derived from Bacillus subtilis PR13, accumulated higher lysine yield of 2.35 mg/ml compared to the wild type. Enhanced  lysine production of 1.47 and 1.32 mg/ml was observed in mutants ART-5 and ART-8 derived from B. subtilis PR9 while, mutant SRT-4 derived from B. pumilus SS16 recorded enhanced lysine accumulation of 2.18 mg/ml. The results obtained in the study showed that L-lysine production by some UV irradiated and AECR mutants was enhanced.