β-1,2-Mannosyltransferases 1 and 3 Participate in Yeast and Hyphae O- and N-Linked Mannosylation and Alter Candida albicans Fitness During Infection

International audiencebeta-1,2-mannosylation of Candida albicans glycoconjugates has been investigated through the identification of enzymes involved in the addition of beta-1,2-oligomannosides (beta-Mans) to phosphopeptidomannan and phospholipomannan. beta-1,2-oligomannosides are supposed to have virulence properties that they confer to these glycoconjugates. In a previous study, we showed that cell wall mannoproteins (CWMPs) harbor beta-Mans in their O-mannosides; therefore, we analyzed their biosynthesis and impact on virulence. In this study, we demonstrate that O-mannans are heterogeneous and that alpha-mannosylated O-mannosides, which are biosynthesized by Mnt1 and Mnt2 alpha-1,2-mannosyltransferases, can be modified with beta-Mans but only at the nonreducing end of alpha-1,2mannotriose. beta-1,2-mannosylation of this O-mannotriose depends on growth conditions, and it involves 2 beta-1,2-mannosyltransferases, Bmt1 and Bmt3. These Bmts are essential for beta-1,2-mannosylation of CWMPs and expression of beta-Mans on germ tubes. A bmt1 Delta mutant and a mutant expressing no beta-Mans unexpectedly disseminated more in BALB/c mice, whereas they had neither attenuated nor enhanced virulence in C57BL/6 mice. In galectin (Gal) 3 knockout mice, the reference strain was more virulent than in C57BL/6 mice, suggesting that the beta-Mans innate receptor Gal3 is involved in C. albicans fitness during infection