Effects of Salinity,Temperature and pH on Relative Protease Activities of Two indigenous Bacillus licheniformis from Hainan

Two Bacillus licheniformis strains Pb-WC09001 and Pb-WC09002 were isolated from the tropical aquacultural systems in Hainan.The effects of salinity,temperatures,and pH on their relative protease activities were determined by the lipid-excluded milk plate assay.With the increase of salinity,the relative enzyme activities of these two strains were on a downward trend,and when salinity increased to 50,Pb-WC09001 still had the ability producing protease and the relative enzyme activity was 1.56 U·mL-1,which suggested that Pb-WC09001 might be more adaptable to high salt environment.In the range of 18—38 ℃(4 ℃ as gradient difference),both strains had the highest relative enzyme activities at 34 ℃.When the culture temperature were at 22 ℃,the relative enzyme activities of Pb-WC09001 were highest;when the culture temperature were at at 30 ℃,the relative enzyme activities of Pb-WC09002 were highest,which suggested that the two strains have produced different type protease under the same temperature,and at low temperatures,Pb-WC09001 has a higher relative enzyme activity than Pb-WC09002.When they were cultured into 2×103/mL at 30 ℃ and the salinity of 30,the most suitable pH values of the highest relative enzyme activity were 8.0 for Pb-WC09001,7.5 for Pb-WC09002,their relative enzyme activities were 2.74 U·mL-1.The results suggested that Pb-WC09001 had higher relative enzyme activities in marine aquaculture environment,especially in lower-temperature seasons.