Candida albicans biofilm formation is associated with increased anti-oxidative capacities

Candida albicans is a common, opportunistic, human fungal pathogen that causes a variety of mucosal and systemic afflictions. It exists in nature both in the biofilm or the sessile phase, as well as in the free-floating or the planktonic phase. Candida biofilms, in particular, display unique characteristics that confer survival advantages over their planktonic counterparts, such as their recalcitrance to common antifungals. The mechanisms underlying Candida biofilm formation and their attributes are poorly understood. In this study, we used a 2-DE-based approach to characterize the protein markers that are differentially expressed in Candida biofilms in comparison to their planktonic counterparts. Using tandem mass spectrometric analysis, we have identified a significant number of proteins including alkyl hydroperoxide reductase, thioredoxin peroxidase, and thioredoxin involved in oxidative stress defenses that are upregulated in the biofilm phase. These proteomic findings were further confirmed by real-time PCR and lucigenin-based chemiluminescence assays. In addition, we demonstrate that a drug target for the new antifungal agent echinocandin, is abundantly expressed and significantly upregulated in Candida biofilms. Taken together, these data imply that the biofilm mode, Candida, compared with their planktonic counterparts, exhibits traits that can sustain oxidative stress (anti-oxidants), and thereby exert resistance to commonly used antifungals.