Mutation Breeding Of Lysozyme-producing Strain And Studies On Fermentation Condition

With UV and ⁶⁰Coγray as the mutation agency radiating lysozyme-producting strain Lysobacter s2-6b, optimal mutagenic conditions were:, UV lamp of 18W, irradiated distance of 28cm, time 15s; ⁶⁰Coγradiation dose of 25Gy. Many high production activity strains were obtained by the first screening and first re-screening.The result of many fermentation experiments in shake flask showed that the enzyme activity of strain UCo1 was 8148.60U/mL and the averyge production of lysozyme was raised by more than 50%.The ability of enzyme production was steady after 10 continuous subcultures.To identify high-yielding strains of UCO1 obtained from mutagenesis, the morphology and the size of the strains were observed by the optical microscope, and the shape, size, color and other characteristics of a single colony on its nutrient agar plate were described. By comparison with the original strain, the results show that the sizes of UCO1 and a single colonie were smaller, the color was deeper but other characteristics changed little.The fermentation conditions of UCo1, including nitrogen source, carbon source, surfactant, inorganic salt, formation time, temperature, pH value and so on, were investigated on shake flask level. The response surface test of the three factors showed that the optimized culture medium was malt sugar 2.0%, Tween-20 0.065%, soybean peptone2.75%. Through shake flask experiments, the optimum fermentation conditions for UCo1 strain were 28℃incubation, formation time 48⁵4 h and initial pH7.0. The enzymatic property test of crude enzyme indicated that optimal temperature was 60⁶5℃, the half life of reaction temperature was 15 min.Optimal pH was 7.0 and it was stable at pH 3.0¹1.0 at room temperature. The inhibition of Li+, Ca2+, Al3+, Cu2+, Pb2+, Mn2+, Zn2+, Fe3+, K+, Mg2+, Na+ on the lysozyme are obvious, in which, the enzyme activity was decreased by 75.8%, 75.3%, 66.8%, 65.6% by Pb2+, Al3+, Mg2+, Ca2+ others by 40 50%. After enzymatic Properties the maximal activity was 11266.7U/mL under the optimum conditions.