Lectin Binding Characteristics of Several Entomogenous Hyphomycetes: Possible Relationship to Insect Hemagglutinins

The hyphomycetous insect pathogens Nomuraea rileyi, Paecilomyees farinosus, Metarhizium anisopliae and Beauveria bassiana were tested with fluorescein isothiocyanate (FITC)-labeled lectins in order to determine cell surface sugars. Concanavalin A, specific for glucose and mannose residues, bound to cell surfaces (hyphal body and/or mycelium) of all fungi examined. Soybean and wheat germ agglutinins (affinities for N-acetylgalactosamine and N-acetylglucosamine, respectively) bound inconsistently to some cell surface areas. Peanut agglutinin, specific for galactose residues, bound to walls of only P. farinosus and B. bassiana. Fungal surface sugar residues may be important with respect to insect defense mechanisms against invading cells. Lectins produced by insects (e.g. Anticarsia gemmatalis and Spodoptera exigua) are known to be specifically inhibited by galactose (or higher concentrations of glucose or mannose). Fungal cells (P. farinosus, B. bassiana) which have exposed galactose residues as detected by FITC-peanut agglutinin appear to be especially efficient in removing hemagglutinin activity from A. gemmatalis and S. exigua hemolymph indicating adsorption of the hemagglutinins to fungal surfaces. Such adsorption may render the fungal cells more susceptible to phagocytosis or other insect defense mechanisms.