The Selection for High-yield Alkaline Protease Producing Strain by Heavy-ion Irradiation

Abstract:

Strain G-41 was isolated from the soil. The strain was identified as Bacillus by 16S rRNA method. Growing in fermentative medium, the strain can produce high-yield alkaline protease (1.7×104 U/mL). We delt with the original strain (G-41) by the heavy-ion irradiation and obtained the mutant G-41-68. The mutant G-41-68 was again treated by the heavy-ion irradiation. We screened a high-yield alkaline protease producing strain 15Gy-54 from many of mutants and its enzyme activity reached to 6.22 × 104 U/mL. Compared with the original strain, the enzyme activity of mutant strains G-41-68 and 15Gy-54 increased by 1.58 and 2.65 times, respectivity. The fermentation conditions of the mutant strain 15Gy-54 were optimized and its enzyme activity further increased, reaching to 7.18 × 104 U/mL. The mutant’s optimum conditions for enzyme production consisted of 1% tryptone, 0.5% yeast extract, 5% lactose, 0.4% Na2HPO4·12H2O, 0.03% KH2PO4, 0.1% Na2CO3, 4 × 10-3 mol/L MgSO4, the initial pH 8.0, shaking culture for 42-48 h, at 41°C. These results showed that the heavy-ion irradiation is an effective method for microbe mutagenesis.

Key words:Heavy-ion irradiation, Bacillus, Alkaline protease, Fermentation