Surface Hydrophobicity Changes of Two Candida albicans Serotype B mnn4Δ Mutants
Department of Pathology, University of Virginia Health System, Charlottesville, Virginia 22908-0904, USA. Eukaryotic Cell
(Impact Factor: 3.18).
05/2005; 4(4):639-48. DOI: 10.1128/EC.4.4.639-648.2005
Cell surface hydrophobicity (CSH) of Candida species enhances virulence by promoting adhesion to host tissues. Biochemical analysis of yeast cell walls has demonstrated
that the most significant differences between hydrophobic and hydrophilic yeasts are found in the acid-labile fraction of
Candida albicans phosphomannoprotein, suggesting that this fraction is important in the regulation of the CSH phenotype. The acid-labile fraction
of C. albicans is unique among fungi, in that it is composed of an extended polymer of β-1,2-mannose linked to the acid-stable region of
the N-glycan by a phosphodiester bond. C. albicans serotype A and B strains both contain a β-1,2-mannose acid-labile moiety, but only serotype A strains contain additional
β-1,2-mannose in the acid-stable region. A knockout of the C. albicans homolog of the Saccharomyces cerevisiae MNN4 gene was generated in two serotype B C. albicans patient isolates by using homologous gene replacement techniques, with the anticipation that they would be deficient in the
acid-labile fraction and, therefore, demonstrate perturbed CSH. The resulting mnn4Δ-deficient derivative has no detectable phosphate-linked β-1,2-mannose in its cell wall, and hydrophobicity is increased
significantly under conditions that promote the hydrophilic phenotype. The mnn4Δ mutant also demonstrates an unanticipated perturbation in the acid-stable mannan fraction. The present study reports the
first genetic knockout constructed in a serotype B C. albicans strain and represents an important step for dissecting the regulation of CSH.
Available from: Susan K Brumfield
- "Presumably cell to cell cohesion within a biofilm could be maintained by a subset of the more specific interactions, while loss of CSH would weaken adhesion to the hydrophobic silicone elastomer surface. Genes implicated in determining CSH include CSH1 [48,49], MNN4  and three genes that contain an eight cysteine domain that shows similarity to a class of fungal hydrophobins (CSA1, PGA10 and RBT5) . CSH1 was upregulated during the time course of detachment, a result that is difficult to interpret since this would presumably enhance binding to the silicone elastomer surface. "
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ABSTRACT: Dispersal from Candida albicans biofilms that colonize catheters is implicated as a primary factor in the link between contaminated catheters and life threatening blood stream infections (BSI). Appropriate in vitro C. albicans biofilm models are needed to probe factors that induce detachment events.
Using a flow through system to culture C. albicans biofilms we characterized a detachment process which culminates in dissociation of an entire early stage biofilm from a silicone elastomer surface. We analyzed the transcriptome response at time points that bracketed an abrupt transition in which a strong adhesive association with the surface is weakened in the initial stages of the process, and also compared batch and biofilm cultures at relevant time points. K means analysis of the time course array data revealed categories of genes with similar patterns of expression that were associated with adhesion, biofilm formation and glycoprotein biosynthesis. Compared to batch cultures the biofilm showed a pattern of expression of metabolic genes that was similar to the C. albicans response to hypoxia. However, the loss of strong adhesion was not obviously influenced by either the availability of oxygen in the medium or at the silicone elastomer surface. The detachment phenotype of mutant strains in which selected genes were either deleted or overexpressed was characterized. The microarray data indicated that changes associated with the detachment process were complex and, consistent with this assessment, we were unable to demonstrate that transcriptional regulation of any single gene was essential for loss of the strong adhesive association.
The massive dispersal of the early stage biofilm from a biomaterial surface that we observed is not orchestrated at the level of transcriptional regulation in an obvious manner, or is only regulated at this level by a small subpopulation of cells that mediate adhesion to the surface.
Available from: Anna Kolecka
- "Indeed, we observed a reduction in biofilm formation, most likely due to a decreased adherence capacity mediated by blocking CR3- RP, by about 28 % in comparison with the control (P,0.001) (Fig. 4). As hydrophobicity of the yeast cell wall is an important factor affecting adherence to different substrates (Hazen et al., 2001; Singleton et al., 2005) and is directly correlated with the surface protein composition, we investigated how it is affected by CR3-RP. The percentage of hydrophobic cells decreased after the preincubation of C. albicans with polyclonal anti-CR3-RP serum from 20.1 to 9.5 % (P,0.001), "
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ABSTRACT: The Candida antigen CR3-RP (complement receptor 3-related protein) is supposed to be a 'mimicry' protein because of its ability to bind antibody directed against the alpha subunit of the mammalian CR3 (CD11b/CD18). This study aimed to (i) investigate the specific humoral isotypic response to immunization with CR3-RP in vivo in a rabbit animal model, and (ii) determine the role of CR3-RP in the adherence of Candida albicans in vitro using the model systems of buccal epithelial cells (BECs) and biofilm formation. The synthetic C. albicans peptide DINGGGATLPQ corresponding to 11 amino-acids of the CR3-RP sequence DINGGGATLPQALXQITGVIT, determined by N-terminal sequencing, was used for immunization of rabbits to obtain polyclonal anti-CR3-PR serum and for subsequent characterization of the humoral isotypic response of rabbits. A significant increase of IgG, IgA and IgM anti-CR3-RP specific antibodies was observed after the third (P<0.01) and the fourth (P<0.001) immunization doses. The elevation of IgA levels suggested peptide immunomodulation of the IgA1 subclass, presumably in coincidence with Candida epithelial adherence. Blocking CR3-RP with polyclonal anti-CR3-RP serum reduced the ability of Candida to adhere to BECs, in comparison with the control, by up to 35 % (P<0.001), and reduced biofilm formation by 28 % (P<0.001), including changes in biofilm thickness and integrity detected by confocal laser scanning microscopy. These properties of CR3-RP suggest that it has potential for future vaccine development.
Available from: Tamara Doering
- "The protein is then further glycosylated in one of two ways, either by the addition of several a(1,3)-linked mannose residues or by extension of the a(1,6)-mannosylation to yield a product known as mannan (Dean, 1999). Commonly found in the outer layer of fungal cell walls, mannans are not essential for in vitro viability, but do influence various characteristics such as cell surface hydrophobicity (Singleton et al., 2005) and flocculation (Stratford, 1992). Generally, mannans have a long a(1,6)-mannose backbone with numerous mannose side chains in various linkages (Ballou et al., 1994; Cutler, 2001; Munro, 2001). "
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ABSTRACT: Glycosyltransferases are specific enzymes that catalyse the transfer of monosaccharide moieties to biological substrates, including proteins, lipids and carbohydrates. These enzymes are present from prokaryotes to humans, and their glycoconjugate products are often vital for survival of the organism. Many glycosyltransferases found in fungal pathogens such as Cryptococcus neoformans do not exist in mammalian systems, making them attractive potential targets for selectively toxic agents. In this article, we present the features of this diverse class of enzymes, and review the fungal glycosyltransferases that are involved in synthesis of the cell wall, the cryptococcal capsule, glycoproteins and glycolipids. We specifically focus on enzymes that have been identified or studied in C. neoformans, and we consider future directions for research on glycosyltransferases in the context of this opportunistic pathogen.
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