Figure 4.

Hyphal growth stimulated by S. oralis is dependent on the Efg1 transcriptional regulator. (A) C. albicans efg1 homozygous deletion mutant (efg1Δ/Δ) and efg1 revertant were grown with or without teal protein expressing S. oralis 34 (green) in 10% BHI-supplemented SSM medium, on Permanox® plastic chamber slides, for 48 hours. Candida cells were stained with Calcoflour White® (blue) and cultures were observed under a fluorescence microscope. The revertant strain formed a mix of yeast and short hyphae in SSM, which were elongated when growing with S. oralis. Bars: 20 μm. (B) Fungal biomass expressed as “genome equivalents” of the efg1Δ/Δ mutant and efg1 revertant strains growing in biofilms with or without S. oralis 34. Biofilms were grown in 6-well polystyrene plates with SSM as the sole nutrient source for 24 h or 48 h. Genome equivalents were extrapolated by analyzing 18 S rRNA gene copy numbers with qPCR in each biofilm well and comparing to a standard curve. Means ± SD are shown from 3 experiments. A higher Candida biomass was noted in biofilms with S. oralis and the efg1 revertant, but not the efg1Δ/Δ mutant, in agreement with the hyphal elongation observed microscopically in the revertant (A). *p < 0.05 and **p < 0.01, for a comparison to C. albicans alone.