Abstract
Enolase is secreted by Candida albicans and is present in its biofilms although its extracellular function is unknown. Here we show that extracellular enolase mediates the colonization of small intestine mucosa by C. albicans. Assays using intestinal mucosa disks show that C. albicans adhesion is inhibited, in a dose dependent mode, either by pretreatment of intestinal epithelium mucosa disks with recombinant C. albicans enolase (70% at 0.5 mg/ml enolase) or by pretreatment of C. albicans yeasts with anti-enolase antibodies (48% with 20 μg antiserum). Also using flow cytometry, immunoblots of conditioned media and confocal microscopy we demonstrate that enolase is present in biofilms and that the extracellular enolase is not an artifact due to cell lysis, but must represent functional secretion of a stable form. This is the first direct evidence that C. albicans' extracellular enolase mediates colonization on its primary translocation site. Also, because enolase is encoded by a single locus in C. albicans, its dual role peptide, as glycolytic enzyme and extracellular peptide, is a remarkable example of gene sharing in fungi.
Highlights
The fungus Candida albicans is a member of the microbiota of healthy individuals
We found that native enolase can be detected in the biofilm matrix of C. albicans SC5314 and in cell lysates of three different C. albicans strains including the SC5314, one clinical isolate identified as a high biofilm producer (L296) and a reference strain that is a low biofilm producer (ATCC90029), used as control (Padovan et al, 2009) (Figure 1C)
These data support previous findings that enolase is present on the cell surface of C. albicans yeasts and indicate for the first time that enolase is present on the surface of hyphae and biofilm-forming cells
Summary
The fungus Candida albicans is a member of the microbiota of healthy individuals. in immunocompromised hosts it causes infections ranging from superficial mucosal to invasive systemic, usually fatal, manifestations (Odds et al, 1988; Dalle et al, 2010). The gastrointestinal (GI) tract, not exclusive, is the main C. albicans reservoir in humans, from which systemic infections are predominantly derived by translocation (Voss et al, 1994; Nucci and Anaissie, 2001). C. albicans secretory aspartyl proteinase, that degrades intestinal mucus, may contribute to pathogenicity by facilitating the penetration of the mucus barrier and the subsequent adhesion/invasion of epithelial cells (Colina et al, 1996). The efficiency of these adhesion/invasion steps is dependent on the expression of different C. albicans molecules that interact with different host receptors. A variety of adhesins are involved in binding to a wide array of proteins on the host’s cell surfaces, including extracellular matrix components (ECM) such as laminin, fibronectin, and fibrinogen (Senet, 1997)
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