Effects of passage on the activities of protease, chitinase and lipase and their relationships with toxicity in Beauveria bassiana

In order to explore the activities of protease, chitinase and lipase in different passage strains of Beauveria bassiana and their toxicity, we selected two high (B5, BXS) and two low toxicity strains (B11, BZ) as the original strains. Then we obtained passage strains of H1, H2, H3 and H4 by repeated passages through the larvae of Monochamus alternatus and R1, R2, R3 and R4 passage strains through a PPDA medium. Toxicity and activities of the original protease, chitinase and lipase and those in the passage strains obtained from both methods were measured, and the relationships between the activities of the three enzymes and LT50 of the corresponding strains were analyzed. The results show that the activities of protease, chitinase and lipase in the four strains (B5, BXS, B11 and BZ) all reduced with the gradual decrease in virulence to M. alternatus after being cultured on the PPDA medium. For those reared with M. alternatus larvae, the activities of three kinds of enzymes in B5, BXS and B11, which were isolated from M. alternatus, tended to increase with increasing virulence, while those of BZ, isolated from Dendrolimus, did not show any clear variation between different generations. Analysis of these relations indicated that LT50 was significantly and negatively correlated with the activities of protease, chitinase and lipase in the original and passage strains of B. bassiana.