Degradation of insect cuticle by Paecilomyces farinosus proteases

Abstract

The entomopathogenic fungus Paecilomyces farinosus showed proteolytic activity in both solid and semi-liquid culture with gelatin as sole N and C source. Semi-liquid cultures were used to characterise proteases. Zymography of crude culture filtrates showed several bands of gelatin degradation in electrophoresis gels. Gel filtration chromatography of these filtrates revealed two peaks of proteolytic activity. Ion-exchange absorption eliminated gelatin from culture filtrates while retaining activity and was used to semipurify P. farinosus proteases. Semipurified culture filtrates had basic pH (8.5 approx.) optimum for proteolytic activity. Treatment of these filtrates with effectors revealed that P. farinosus proteases are serine proteases containing sulphydryl groups. Isoelectrofocusing combined with zymography revealed the presence of several active basic isoforms. Larvae of the lepidopteran Galleria mellonella showed cuticle damage and protein release 1h after incubation with semipurified extracts of P. farinosus. These results indicate that proteolytic enzymes could be involved in insect host penetration by P. farinosus.