A Histone Deacetylase Complex Mediates Biofilm Dispersal and Drug Resistance in Candida albicans

Abstract

Biofilms are resilient, surface-associated communities of cells with specialized properties (e.g., resistance to drugs and mechanical forces) that are distinct from those of suspension (planktonic) cultures. Biofilm formation by the opportunistic human fungal pathogen Candida albicans is medically relevant because C. albicans infections are highly correlated with implanted medical devices, which provide efficient substrates for biofilm formation; moreover, biofilms are inherently resistant to antifungal drugs. Biofilms are also important for C. albicans to colonize diverse niches of the human host. Here, we describe four core members of a conserved histone deacetylase complex in C. albicans (Set3, Hos2, Snt1, and Sif2) and explore the effects of their mutation on biofilm formation. We find that these histone deacetylase complex members are needed for proper biofilm formation, including dispersal of cells from biofilms and multifactorial drug resistance. Our results underscore the importance of the physical properties of biofilms in contributing to drug resistance and dispersal and lay a foundation for new strategies to target biofilm dispersal as a potential antifungal intervention.

Plasticity of Candida albicans Biofilms

“…The rate plateaued at approximately 24 h (188). Nobile et al (190) subsequently demonstrated, in a variation of the Douglas model using Spider medium, that the rate of accumulation of budding yeast cells in the medium decreased between 24 and 60 h. It was not clear whether the yeast-phase cells accumulating in the medium originated in the adhesive yeast cell basal layer, were released from the hyphal upper layer, or were released from yeast cell pockets within the hyphal upper region of the developing biofilm. The lowest rate of release was observed in RPMI 1640 (MOPS) medium, which is consistent with the observation that biofilms formed in this medium contain vertically oriented hyphae with few lateral yeast cells (45,183,184).…”

Assessment and Optimizations of Candida albicans In Vitro Biofilm Assays

“…The 96-and 384-well optical density assays are derivatives of the previously reported 96-well protocols (17,33). These assays use flat-bottomed, non-tissue culture-treated 96-well (catalog number 351172; BD Falcon) or 384-well (catalog number 242765; Thermo) plates.…”

“…Other assays infer biofilm formation on the basis of measurements of cell viability {e.g., metabolic reduction of the tetrazolium salt reagent 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) (27,28) or 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) (29,30)} or by the uptake of dyes or stains (e.g., crystal violet incorporation into the biofilm [31]). Specialized assays have also been developed to examine specific stages of biofilm development; for example, the number of cells dispersed from an established biofilm can be monitored by CFU counts, hemocytometer counts, and/or optical density measurements (32,33). Other specialized assays examine factors like growth in a microfluidic chamber (18,34,35), active attachment to a surface other than the bottom of a polystyrene plate (34), or the ability of drugs to penetrate into an established biofilm (36).…”

“…We refer to this assay as the cell adhesion assay. Third, we developed two types of assays (called the standard dispersal assay and the sustained dispersal assay) to quantify cell dispersion at different stages of biofilm development, using only a standard plate reader for analysis (33). Finally, we developed an assay to observe biofilm formation under linear flow in a microfluidic device where adherence and cellular morphology can be visually and temporally tracked using time-lapse microscopy throughout the process of biofilm development (35).…”

“…First, we established an assay based on the OD at 600 nm (OD 600 ) to rapidly screen large numbers of conditions and to track the same condition over multiple time points (17,33,35). Second, we also developed a new assay to quantitatively determine the number of cells adhering to a surface in the first stage of biofilm development (35).…”