Candida albicans is a polymorphic fungus that can grow as yeast (Y) and hypha (H). The Y-H morphological switching is controlled through the MAPK, Cek1p. With the prior work showing that occidiofungin prevents C. albicans from forming hypha when added at the time of Y-H switching, we aim to identify the impact of occidiofungin on signaling events associated with morphological switching specifically looking at Cek1 MAPK cascade. Results from this work have demonstrated that Cek1 MAPK is not required for occidiofungin bioactivity. Further, we report that morphologically switching cells are more sensitive to occidiofungin than their non-switching counterparts. Moreover, later stages of hyphal formation exhibit increased sensitivity towards occidiofungin suggesting occidiofungin targets hyphal initiation and/or elongation process. This work also demonstrates that addition of occidiofungin beyond a discrete time window required for hyphal initiation has minimal effect on hyphae formation and elongation.

Several published functions associated with the CHK1 histidine kinase of Candida albicans resemble those of the MAPK Cek1p and its cognate receptor Sho1p (SSU81). To explore this further, we have compared mutants lacking the proteins mentioned above and have constructed a double sho1/chk1Δ null mutant to determine relationships among these proteins. We observed that the sensitivity to Congo red (CR), calcofluor white (CW), as well as clumping of cells, was slightly increased in the double mutant compared to the single chk1Δ or sho1Δ mutants. However, Cek1p phosphorylation via Sho1p, which occurs during log phase growth in the presence or absence of CR in Wt cells, does not require Chk1p. These data suggest that Chk1p and Sho1p are components of parallel but independent signal pathways. In addition, bulk mannan of strains was analyzed by GLC/MS and GPC MALLS and NMR. Compared to Wt and a CHK1 gene-reconstituted strain (CHK23) that contained high, intermediate and low Mw mannan species, we found that the mannan of strains CHK21 (chk1Δ null), the cek1Δ null, and the double mutant consisted only of low Mw mannan. The sho1Δ null mutant only demonstrated a reduced intermediate type of mannan. Alcian blue binding was lower in cek1Δ, chk1Δ, and the double sho1/chk1Δ null mutant lacking high and intermediate Mw mannan than in the sho1Δ null which had a partial loss of intermediate Mw mannan only. We conclude that the Chk1p HK is part of a functionally similar but parallel pathway to the Sho1p-Cek1p pathway that confers resistance to the cell wall inhibitors CR and CW. However, a functional relationship in mannan biosynthesis of Chk1p and Cek1p exists that only partially requires Sho1p.