Surface Hydrophobicity Changes of Two Candida albicans Serotype B mnn4 Mutants

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 -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 -1,2-mannose acid-labile moiety, but only serotype A strains contain additional -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 mnn4 -deficient derivative has no detectable phosphate-linked -1,2-mannose in its cell wall, and hydrophobicity is increased significantly under conditions that promote the hydrophilic phenotype. The mnn4 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.