Proteins that are covalently linked to the skeletal polysaccharides of the cell wall of Candida albicans play a major role
in the colonization of the vaginal mucosal surface, which may result in vaginitis. Here we report on the variability of the
cell-wall proteome of C. albicans as a function of the ambient O-2 concentration and iron availability. For these studies,
cells were cultured at 37C in vagina-simulative medium and aerated with a gas mixture consisting of 6% (V/V) CO2, 0.01-7%
(v/v) O-2 and N-2, reflecting the gas composition in the vaginal environment. Under these conditions, the cells grew exclusively
in the non-hyphal form, with the relative growth rate being halved at similar to 0.02% (V/V) O-2. Using tandem MS and immunoblot
analysis, we identified 15 covalently linked glycosylphosphatidylinositol (GPI) proteins in isolated walls (Als1, Als3, Cht2,
Crh11, Ecm33, Hwp1, Pga4, Pga10, Phr2, Rbt5, Rhd3, Sod4, Ssr1, Ywp1, Utr2) and 4 covalently linked non-GPI proteins (MP65,
Pir1, Sim1/Sun42, Tos1). Five of them (Als3, Hwp1, Sim1, Tos1, Utr2) were absent in cells grown in rich medium. Immunoblot
analysis revealed that restricted 02 availability resulted in higher levels of the non-GPI protein Pir1, a putative beta-1,3-glucan
cross-linking protein, and of the GPI-proteins Hwp1, an adhesion protein, and Pga10 and Rbt5, which are involved in iron acquisition.
Addition of the iron chelator ferrozine at saturating levels of O-2 resulted in higher cell wall levels of Hwp1 and Rbt5,
suggesting that the responses to hypoxic conditions and iron restriction are related.