Regulation of Candida albicans morphogenesis by fatty acid metabolites

Abstract

Candida albicans is an opportunistic dimorphic fungus that inhabits various host mucosal sites. Conversion from the yeast to the hyphal form has been associated with increased virulence and mucosal invasiveness. C. albicans morphogenesis is regulated by multiple signals and signaling pathways. However, signals that control morphogenesis in vivo are unknown. We investigated the effects of host long chain fatty acids, eicosanoids, and bacterial short chain fatty acids on control of germination. None of the C18 or C20 fatty acids tested had an effect on enhancing germ tube formation (arachidonic acid, oleic acid, linolenic acid, or gamma-linolenic acid). Among the different eicosanoids, both prostaglandin E2 and thromboxane B2 significantly enhanced serum-induced germination by C. albicans. Addition of antiprostaglandin or antithromboxane antibodies to serum alone inhibited germ tube formation by almost 30%, while control antibody had no effect, indicating that these eicosanoids are major morphogenic factors in the serum. Since these molecules also bind to albumin, this may also explain the hyphal transforming activity in serum that associates with albumin. Interestingly, short chain fatty acids (butyric acid), the product of lactic acid bacteria (LAB), inhibited germination. In addition, LAB culture supernatants as well as live LAB also inhibited C. albicans morphogenesis. Overall, these results indicate that fatty acid metabolites and fatty acid pathways can up-regulate and down-regulate germination in C. albicans.

Figures

FIG. 1.

Effect of long chain fatty acids on C. albicans morphogenesis. Long chain fatty acids (Caymen Chemicals) or carrier (1× PBS) was added to C. albicans diluted in 100% FBS to a final concentration of 0.1 nM at neutral pH. Cultures were incubated at 37°C to induce germination, and germ tube formation was measured after 2 h with the crystal violet germ tube assay. Results are expressed as percent control (% control = A540 for experimental well/A540 for control well). Background absorbances (A450 of the well containing 100% PBS) were subtracted out. The assay was performed in triplicate and repeated two times with similar results. *, P < 0.05 as determined by the Student's t test. AA, arachidonic acid; LNA, linolenic acid; OA, oleic acid.

FIG. 2.

Effect of eicosanoids on C. albicans morphogenesis. Eicosanoids (Caymen Chemicals) or carrier (1× PBS) was added to C. albicans diluted in 100% FBS to a final concentration of 0.1 nM at neutral pH. Germination was measured as described in the legend to Fig. 1. Background absorbances (A450 of the well containing 100% PBS) were subtracted out. The assay was performed in triplicate and repeated two times with similar results. PG, prostaglandin; Tx, thromboxane; HHT, hydroxyheptadecatrienoic acid; LT, leukotriene. *, P < 0.05 as determined by Student's t test.

FIG. 3.

Effect of antiprostaglandin or antithromboxane antibody on C. albicans morphogenesis in FBS. Polyclonal antiprostaglandin antibody, anti-TxB2 antibody (Cayman Chemicals), control rabbit IgG (BD Pharmingen, San Diego, Calif.), or carrier (1× PBS) was added to C. albicans yeast diluted in 100% FBS. Germination was measured as described in the legend to Fig. 1. The assay was performed in triplicate and repeated two times with similar results. Anti-PG, antiprostaglandin antibody *, P < 0.05 as determined by Student's t test.

FIG. 4.

Effect of live or heat-killed LAB on C. albicans morphogenesis. Lactobacillus spp. were grown in MRS broth for 24 h under microaerophilic conditions at 37°C at neutral pH. Live or heat-killed lactobacilli diluted in MRS broth or carrier (MRS broth) were added to C. albicans diluted in 100% FBS at various ratios of LAB to C. albicans. Germination was measured as described in the legend to Fig. 1. The assay was performed in triplicate and repeated two times with similar results. *, P < 0.05 as determined by Student's t test. CA, C. albicans.

FIG. 5.

Effect of LAB culture supernatants on C. albicans morphogenesis. Lactobacillus spp. were grown in Lactobacillus MRS broth for (a) 2 h or (b) 24 h under microaerophilic conditions at 37°C. Lactobacillus culture supernatants (sups) from these two time points or carrier (MRS broth) was added to C. albicans diluted in 100% FBS at neutral pH. Germination was measured as described in Materials and Methods. The assay was performed in triplicate and repeated two times with similar results. *, P < 0.05 as determined by Student's t test.

FIG. 6.

Effect of SCFA on C. albicans morphogenesis. SCFA at various concentrations (Sigma Chemical Co., St. Louis, Mo.) or carrier (1× PBS) was added to C. albicans diluted in 100% FBS and adjusted to neutral pH. Germination was measured as described in the legend to Fig. 1. The assay was performed in triplicate and repeated two times with similar results. *, P < 0.05 as determined by Student's t test.