Contribution of N-Linked Mannosylation Pathway to Candida parapsilosis and Candida tropicalis Biofilm Formation

BACKGROUND: Mycoses are a growing threat to human health, and systemic candidiasis caused by Candida parapsilosis and Candida tropicalis is frequent in immunocompromised patients. Biofilm formation is a virulence factor found in these organisms, as sessile cells adhere to surfaces, the stratification and production of extracellular matrix provides protection and resistance to antifungal drugs. Previous evidence indicated that the N-linked mannosylation pathway is relevant to C. albicans biofilms, but its contribution to other species remains unknown. METHODS: C. parapsilosis and C. tropicalis och1∆ mutants, which have a disrupted N-linked mannosylation pathway, were used to form biofilms. In addition, wild-type and mutant cells were also treated to remove N-linked mannans or block this pathway. Biofilms were analyzed by quantifying the included fungal biomass, and extracellular matrix components. Moreover, gene expression and secreted hydrolytic enzymes were also quantified in these biofilms. RESULTS: The och1∆ mutants showed a reduced ability to form biofilms in both fungal species when compared to the wild-type and control strains. This observation was confirmed by trimming N-linked mannans from walls or blocking the pathway with tunicamycin B. According to this observation, mutant, and treated cells showed an altered composition of the extracellular matrix and increased susceptibility to antifungal drugs when compared to control or untreated cells. The gene expression of secreted virulence factors, such as aspartyl proteinases and phospholipases, was normal in all the tested cells but the secreted activity was reduced, suggesting a defect in the secretory pathway, which was later confirmed by treating cells with brefeldin A. CONCLUSION: Proper N-linked mannosylation is required for biofilm formation in both C. parapsilosis and C. tropicalis. Disruption of this posttranslational modification affected the secretory pathway, offering a link between glycosylation and biofilm formation.