Variations in the ability of galactose and mannose-specific lectins to bind to cell wall surfaces during growth of the insect pathogenic fungus Paecilomyces farinosus.

The arrangement of carbohydrate molecules on surfaces of fungal cells may play an important role in nonself recognition of these microorganisms by potential invertebrate hosts. Changes in the ability of various galactose and mannose-specific lectins to bind to surface components on cell walls of the insect pathogen Paecilomyces farinosus were therefore examined during growth and differentiation of the fungus. Fluorescein isothiocyanate conjugates of concanavalin A (Con A, specific for alpha-D-mannose) and peanut agglutinin (PNA, beta-D-galactose) bound inconsistently to blastospores and weakly to mycelia except at apical regions where strong fluorescence was observed. Labeling patterns were similar on cells tested with a galactose-specific lectin purified from Spodoptera exigua (beet armyworm) hemolymph, but Bandeiraea simplicifolia lectin (BS-I alpha-D-galactose) bound only to mycelia. Electron microscopy using ferritin and gold probes showed that the galactomannans are located in a loosely bound coating on the cell wall surface. Variations in lectin binding patterns are apparently due to absence (e.g., by shedding) of the coat or to rearrangement of carbohydrate components in the coat. Staining of Western blots of dithiothreitol (DTT) cell wall extracts further indicated that the BS-I-binding entity is a unique component of the mycelial surface since, as in the fluorescence studies, blastospore preparations were not labeled. Staining of blastospore blots with other galactose-specific probes (e.g., PNA) was comparable to staining of mycelial blots.(ABSTRACT TRUNCATED AT 250 WORDS)