Adherence of Candida albicans germ tubes to plastic: ultrastructural and molecular studies of fibrillar adhesins

Abstract

Germ tubes of Candida albicans produced an additional fibrillar surface layer responsible for enhanced adherence to plastic. The correlation between germination of C. albicans and adherence of germ tubes to a plastic matrix led us to consider the existence of germ tube-specific adhesive components involved in the attachment process. Using concanavalin A-sensitized latex microspheres, we first detected extracellular molecules on the plastic surface after removal of the adherent germ tubes. Electron microscopy confirmed that fibrils of the germ tube involved in cell-substratum interconnections were retained on the plastic surface. Cytochemistry with concanavalin A-gold labeling demonstrated that these fibrillar structures contained mannoproteins. Dithiothreitol and iodoacetamide treatment of washed plastic allowed us to further characterize these fibrillar adhesins. Through analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two components with molecular weights (MWs) of 68,000 and 60,000 were detected on the plastic surface. The 68,000-MW component appeared to be one of the major constituents of the germ tube surface layers. Biosynthetic labeling experiments performed with L-[35S]methionine revealed two additional proteins: a high-MW component (greater than 200,000), and a 200,000-MW component. These four proteins, strongly labeled on the plastic surface and on the germ tube cell wall layers, were in contrast slightly labeled or even nonidentified in the culture supernatant, suggesting their involvement in germ tube adherence.