Isolation of microbial strain producing thermostable protease and characterization of the enzyme

In order to provide protease for potential use in aquaculture feed industry,the strain producing thermostable protease was screened from the environment of maar lake.Thirty strains were isolated from soil by milk plates.Strain HL-3,which showed the highest production,was screened according to fermenting in shaking flasks,and the enzymatic activity of protease in culture solution of HL-3 was 399.2 U / mL.Based on physiological and biochemical identification,16S rDNA sequence and phylogenetic analysis,the strain HL- 3 was preliminarily identified as Bacillus licheniformis. The protease activity preformed optimally at70 ℃ and p H7.0. The protease retained 75.12% of its original activity after incubation for 10 min at 90 ℃. When ion concentration reached 1.0 × 10~(-3)mol / L,metal ions of Cu~(2+) and Mn~2+) would strongly inhibit the protease activity,metal ions of Fe~(2+),Zn~(2+)and Ca~(2+) would activate the protease activity,metal ions of Mg~(2+) and K~+would not affect the protease activity.The protease produced by strain HL-3 in this study may have the potential in aquaculture feed industry.