The role of mucilage in the attachment of conidia, germ tubes, and appressoria in the saprobic aquatic Hyphomycetes Lemonniera aquatica and Mycocentrospora filiformis

Abstract

Spore attachment of the saprobic aquatic Hyphomycetes Lemonniera aquatica and Mycocentrospora filiformis was compared on Thermanox cover slips at the scanning and transmission electron microscope levels. The strength of attachment to Perspex discs was measured with the Fowler cell adhesion measurement module. Data are presented on the initial attachment of conidia and subsequent attachment of germ tubes, hyphae, and appressoria. Attachment at all stages was mediated by mucilage. Both fungi exhibited a similar strength of initial conidial attachment, but attachment resulted from different strategies: (i) in L. aquatica, by active release of mucilage as a result of a thigmotropic response to the substratum; (ii) in M. filiformis, by a passive process involving attachment by pre-existing conidial mucilage prior to contact with the substratum. The strength of attachment increased with settlement time. A fast germination rate, concurrent with mucilage production, resulted in the firm attachment of L. aquatica conidia, while initial germination in M. filiformis was slow and this corresponded to a comparatively weaker conidial attachment. Further increase in the strength of attachment was the result of greater hyphal development, and most importantly, by appressorium formation. All these structures were enrobed in a mucilaginous sheath, although variations were observed in the morphology and texture of mucilages. This suggested differences in chemical composition of mucilage (i) between the two fungi, and (ii) among different structures of the same fungus. Keywords: aquatic Hyphomycetes, appressorium, attachment, germination, mucilage, ultrastructure.