Fucose-specific adhesins on germ tubes of Candida albicans

Abstract

Lectin-like adhesins of hyphal-form Candida albicans were investigated by conventional fluorescence microscopy, fluorescence microscopy with image analysis, spectrofluorimetry and flow cytometry. Labelling was done with neoglycoprotein probes consisting-of sugars (fucose, mannose, glucose, galactose, lactose) covalently linked to bovine serum albumin (BSA), which itself was labelled with fluorescein. The fucose probe bound to both the yeast and germ-tube portions of hyphal-form cells, not especially at the tip, but in the adjacent region of the germ-tube portion. Probes with the other sugars did not label the hyphal-form cells. Fucose-probe binding to the cells was optimal at pH 5.0 in citrate buffer, and was a time-dependent reaction requiring 30-60 min and reaching saturation concentration at 100 mu g ml(-1). Each hyphal-form cell of C. albicans grown in 199 medium was calculated to have about 2x10(7) fucose probe-binding sites. There appeared to be no requirement for Ca2+ or Mg2+ in binding. Binding of the fucose probe to the hyphal-form cells was higher at 37 degrees C than at 22 degrees C or 4 degrees C, Fluorescence intensity of the fucose-labelled yeast forms was not increased over the hyphal-form cells. A germ-tube-deficient mutant when exposed to hyphal-form growth conditions for 2 h showed much less binding of the fucose probe than the wild-type which produced germ tubes. Confirmation of specificity and the need for a carrier molecule was obtained by showing that Fuc-BSA (without fluorescein) effectively inhibited the binding of the fucose probe, although L-fucose itself was inactive, as was Gal-BSA. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.