Effects of cryopreservation and freeze-drying on proteases enzymatic activity of entomopathogenic strains of Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metchnikoff) Sorokin.

Abstract

Beauveria bassiana and Metarhizium anisopliae are fungal species known for their entomopathogenic activity; they represent an important alternative to chemical control of many pest insects and appropriate preservation methods are thus necessary to maintain their properties over time. In the present study the effects of cryopreservation and freeze­drying were investigated on virulence determinants such as proteases and specifically on subtilisin-type Pr 1 and Pr 2 that seem to play a predominant role in insect fungal penetration. Three Metharizium anisopliae strains (M 13/ I05, M 13/ I12 and M 13/ I33) and three Beauveria bassiana strains (B 13/ I03, B 13/ I57 and B 13/ I63) were tested. Data obtained from our experiments show that the decrease of Pr 1 and Pr 2 enzymatic activity in B. bassiana and M. anisopliae strains 7 months after storage does not affect their entomopathogenic ability against larvae of Tenebrio molitor compared to the fresh cultures before storage. The role of Pr 1 and Pr 2 as predominant factors in the entomopathogenicity of both fungal species is discussed. No significant differences were found in any strain tested for morphological features using both preservation methods.