Ultrastructure of proteinase-secreting cells of Candida albicans studied by alkaline bismuth staining and immunocytochemistry

Abstract

The ultrastructure of Cundida ulbicans cells induced to secrete extracellular proteinase (EPR) has been studied. Electron microscopy employing alkaline bismuth staining, a method which stains polysaccharides, clearly revealed Golgi-like bodies and secretory vesicles in C. albicans cells. After EPR induction, there was no apparent increase in the number of these structures. Instead, many flocculent granules appeared at the periphery of induced cells. The granules were similar to secretory vesicles in size, but were more irregular in shape. Similar granules were observed in non-induced cells, though less frequently than in induced cells. Brefeldin A, a specific inhibitor of membrane transport in the secretory pathway, caused the accumulation of EPR and Golgi-like bodies in EPR-induced cells, but did not affect the accumulation of the granules, These results suggest that the granules are unrelated to EPR secretion. Electron microscope immunocytochemistry with affinity-purified anti-EPR antibodies showed that the granules in EPR-induced cells were recognized by the antibodies. This recognition was completely inhibited by the presence of glycogen, suggesting that antibodies cross-react with glycogen-like polysaccharides in the granules. Although the location of EPR within the cells remains unclear, the results suggest that EPR might be secreted via the constitutive secretory pathway, and that EYR is glycosylated to give a structure with some similarity to glycogen.

Localized accumulation of cell wall mannoproteins and endomembranes induced by brefeldin A in hyphal cells of the dimorphic yeastCandida albicans

“…1981, Schekman 1985. BFA treatment at 35 gM increased the occurrence of a stack of membrane cisternae in hyphal forms, as we already observed in yeast-form cells of C. albicans (Akashi et al 1993). The cisternae reacted with the antibodies.…”

“…We expected that these unique effects of BFA would facilitate observations of the intracellular distribution of this organelle. In C. albicans, BFA caused the accumulation of an acid phosphatase (Arioka et al 1991) and an acid proteinase (Akashi et al 1993) that would normally be secreted, but it did not appear to affect DNA replication or protein synthesis (Hayashi et al 1982). These results strongly suggest that BFA is an effective inhibitor of secretory transport in C. albicans.…”

“…Brefeldin A (BFA) is a fungal metabolite that affects membrane trafficking and has been used to analyze the mechanism of secretory transport in many organisms (for a review, see Klausner et al 1992). BFA has increased the occurrence of Golgi cisternae and the number of cisternae in the stack in the yeast form of Candida albicans (Akashi et al 1993), and it has increased the complexity of the Golgi cisternae in the filamentous fungus Magnaporthe grisea (Bourett and Howard 1996). We expected that these unique effects of BFA would facilitate observations of the intracellular distribution of this organelle.…”

KEX2 Influences Candida albicans Proteinase Secretion and Hyphal Formation

“…The tetrapeptide, YEFD, necessary for the maintenance of Kex2 in the TGN of S. cerevisiae (38) is perfectly conserved in the predicted cytoplasmic domain of the C. albicans protein. In the TGN, C. albicans Kex2 would thus be in a position to interact with the Candida Saps, which based on biochemical, ultrastructural, and genetic criteria appear to transit through the yeast classical secretory pathway (45,46).…”

A cytochemical study of acid carbohydrates on the surface of Candida lipolytica grown in tween 80-containing medium

“…The walls are composed mostly of mannoproteins and fibrous and branched glycans that link other components of the wall such as chitin, as demonstrated by biochemical and degradative techniques. Carbohydrate-containing molecules have been located on the yeast cell wall by ultrastructural cytochemistry (2,5,6,8,16,20,28,30,31,48,56).…”