Enzymatic studies of the extracellular mucilage of two aquatic hyphomycetes, Lemonniera aquatica and Mycocentrospora filiformis

The effect of three carbohydrate-digesting enzymes, β-glucuronidase, lyticase and α-mannosidase, and three proteolytic enzymes, α-chymotrypsin, papain and pronase E, on the strength of conidial attachment of Lemonniera aquatica and Mycocentrospora filiformis was determined using the LH-Fowler Cell Adhesion Measurement Module. Carbohydratedigesting enzyme treatments showed significant differences in number of attached and detached conidia versus control samples; little or no effect was observed for the proteolytic enzymes. Scanning and transmission electron microscopy showed different degrees of mucilage digestion by the carbohydrate-digesting enzymes on the germ hyphae, hyphae subtending appressoria, and appressoria of the two species. The loss of mucilage integrity and decrease in mucilage thickness were more pronounced on the hyphal sheaths than on the appressorial sheaths. Lyticase caused the most severe damage to the mucilage and cytoplasm of both fungi, particularly L. aquatica. β-Glucuronidase and a-mannosidase exhibited more effective mucilage digestion on M. filiformis than on L. aquatica. Results indicate that the mucilage of the two species is mainly polysaccharide, containing more β-l,3-glucans than β-glucuronide and a-mannosyl residues. Variability of mucilage composition exists between these species and also between different structures of the same fungus.