Candida albicans SET3 Plays a Role in Early Biofilm Formation, Interaction With Pseudomonas aeruginosa and Virulence in Caenorhabditis elegans

Abstract

The yeast Candida albicans exhibits multiple morphologies dependent on environmental cues. Candida albicans biofilms are frequently polymicrobial, enabling interspecies interaction through proximity and contact. The interaction between C. albicans and the bacterium, Pseudomonas aeruginosa, is antagonistic in vitro, with P. aeruginosa repressing the yeast-to-hyphal switch in C. albicans. Previous transcriptional analysis of C. albicans in polymicrobial biofilms with P. aeruginosa revealed upregulation of genes involved in regulation of morphology and biofilm formation, including SET3, a component of the Set3/Hos2 histone deacetylase complex (Set3C). This prompted the question regarding the involvement of SET3 in the interaction between C. albicans and P. aeruginosa, both in vitro and in vivo. We found that SET3 may influence early biofilm formation by C. albicans and the interaction between C. albicans and P. aeruginosa. In addition, although deletion of SET3 did not alter the morphology of C. albicans in the presence of P. aeruginosa, it did cause a reduction in virulence in a Caenorhabditis elegans infection model, even in the presence of P. aeruginosa.

Keywords: Caenorhabditis elegans; Candida albicans; Pseudomonas aeruginosa; SET3; biofilm.

Figure 1

Effect of SET3 deletion on Candida albicans monomicrobial biofilms. Monomicrobial biofilm biomass after 6 h (A) and 48 h (B) of the homozygous mutant of SET3 (set3Δ/Δ) as well as the homozygous mutant with add-back of the wild-type gene (set3Δ/Δ::SET3). Colony forming units (CFU) of mature C. albicans biofilms are indicated in (C) as well as biofilm morphology of mature biofilms in (D) (SC5314), (E) (set3Δ/Δ) and (F) (set3Δ/Δ::SET3). Small panels on right corners indicate biofilms with lower magnification. Scale bars on all panels indicate 10 μm. *Significantly different from wild type (SC5314) (****P < 0.0001).

Figure 2

Effect of SET3 deletion on Candida albicans polymicrobial biofilms with Pseudomonas aeruginosa. Polymicrobial biofilm biomass after 6 h (A) and 48 h (B) of the homozygous mutant of SET3 (set3Δ/Δ) as well as the homozygous mutant with add-back of the wild-type gene (set3Δ/Δ::SET3) with P. aeruginosa. Colony forming units (CFU) of mature C. albicans biofilms are indicated in (C) and P. aeruginosa CFUs in (D, E) indicates the ratio of bacterial/fungal CFUs. (F) (SC5314), (G) (set3Δ/Δ) and (H) (set3Δ/Δ::SET3) indicates the morphology of mature polymicrobial biofilms. Small panels on right corners indicate biofilms with lower magnification. Scale bars on all panels indicate 10 μm. *Significantly different from wild type (SC5314) (*P < 0.05; **P < 0.005).

Figure 3

Survival of Caenorhabditis elegans infected with Candida albicans mutants and Pseudomonas aeruginosa. (A) - Percentage survival of C. elegans infected with C. albicans wild type (SC5314) or the homozygous mutant of SET3 (set3Δ/Δ) as well as the homozygous mutant with add-back of the wild-type gene (set3Δ/Δ::SET3). (B) – Percentage survival of C. elegans co-infected with C. albicans mutants and P. aeruginosa (PAO1). Controls consists of C. elegans allowed to feed on Escherichia coli OP50 (OP50). The tables represent median lifespan with standard error (S. E.) along with days to reach 50% mortality. P-values are included for the Log-rank test for overall differences in survival. *Significantly different from wild type C. albicans (SC5314).