Mutation Breeding of Thermostable Lipase Producing Strain Wi-3 and Study on Its Lipase Properties

A thermostable lipase producing strain Wi-3 was isolated from the soil samples collected from the drain of a hot spring bathhouse in Fuzhou city.Two mutant strains of Wi-3-3 and Wi-3-5 were selected after mutation by ultraviolet(UV) combined with N-methyl-N-nitro-N-nitrosoguanidin(NTG).Compared to that of the wild type strain of Wi-3,the lipase activities of the two strains were increased 32.3% and 11.8%,respectively.Studies on the conditions of Wi-3-3 for lipase producing showed that the lipase production was highest at the culture temperature of 35℃,initial pH value of 7.0,medium volume of 35 mL in 250 mL flask and inoculum volume of 4 mL(mycelium concentration of 1.5×108 unit·mL-1).The crude lipase was extracted by ammonium sulfate precipitation,and the properties of the lipase were preliminarily studied.The results indicated that the crude lipase showed highest activity at the pH value of 8.6 and the temperature of 55℃.