Candida Tropicalis Biofilm Formation Under Secondary Bile Salt Sodium Deoxycholate

Candida species are components of the normal intestinal microbiota and are under constant exposure to bacterial metabolites, including secondary bile salts. Secondary bile salts are produced by commensal bacteria in the intestine and not only affect lipid absorption through emulsification but also have great effects on other microorganisms. Here, we examined the effect of a secondary bile salt, sodium deoxycholate (NaDCA), on the formation of biofilms by Candida tropicalis. In contrast to C. albicans, C. tropicalis tended to maintain its absolute biofilm biomass and surface hydrophobicity in the presence of NaDCA. Fluorescent 3D microscopic imaging of the biofilm revealed that NaDCA treatment reduced filamentous projection to the top of the biofilm. RNA-seq analysis revealed that some genes, especially those associated with iron metabolism, were differentially expressed in NaDCA-treated C. tropicalis. Although NaDCA altered the appearance of C. tropicalis biofilms, analysis of the expression of key virulence factor genes encoding agglutinin-like sequences and candidalysin revealed that these genes were less affected by NaDCA in C. tropicalis than in C. albicans. High-iron exposure had a negative effect on C. tropicalis biofilm biomass. These results suggest a difference in the intestinal niche occupied by C. albicans and C. tropicalis according to the local availability of secondary bile salts.