Production of cuticle - degrading proteases by Beauveria bassiana and their induction in different media

Abstract

The concern for the development of hyphomycete fungi as suitable biocontrol agents of insect pests leads to the isolation of various insect pathogenic fungi. Amongst them, one of the most studied entomopathogenic fungus is Beauveria bassiana. The conidia of mitosporic fungi adhere to the host cuticle and germinate to produce an infectious propagule, and produce a sequential release of extra cellular enzymes to breach the insect cuticle. Protease is one of the most important and earliest enzymes involved in the host invasion. Extracellular protease production by seventeen B. bassiana isolates was investigated in the present study. High protease activity was observed during four to six days of culture incubation. Induction mechanism of subtillisin type Pr1 and trypsin type Pr2 activity were investigated utilizing different media. Minimal medium supplemented with casein (1%) showed high protease production and minimal medium supplemented with colloidal chitin (2%) was also able to induce Pr1 activity. The pH, ammonia and oxalic acid production in in vitro conditions was also investigated and the alteration in pH for protease production was not significant irrespective of the medium used. The protease activity gel was also studied and a common 66 kDa protease was observed in all the seven isolates studied. Key words: Ammonia, B. bassiana, oxalic acid, subtillisin type Pr1, trypsin type Pr2, protease, pH.