Fig 3.

Growth of C. albicans in the presence of cysteine results in sulfite formation in culture supernatants. (A) Sulfite production was inspected in the supernatants of the wild type, mutants CDG1M4A/B (cdg1Δ), and complemented strains CDG1KS2A/B (cdg1Δ + CDG1) after 24 h of growth in SD medium containing 10 mM cysteine. Supernatants of the wild type grown for 24 h in SD medium without cysteine and uninoculated SD medium with 10 mM cysteine were used as controls. The results are means ± the SD from three independent experiments. Sulfite as SO₂ was not detectable in supernatants of the cdg1Δ mutant compared to wild type and complemented strain. The asterisk (*) indicates that the detected difference was significant (P < 0.05). The independently constructed A/B mutants behaved identically, and the results for only one of them are shown. (B) Overnight precultures of wild type, SSU1M4A (ssu1Δ), CDG1M4A/B (cdg1Δ), complemented strains CDG1KS2A/B (cdg1Δ + CDG1), and ssu1Δ cdg1Δ double mutants were diluted 1:100 in fresh SD medium containing various concentrations of cysteine. The optical densities of the cultures were measured after growth for 8 h and 24 h at 30°C. The results are means ± the SD from three independent experiments. (C) qRT-PCR measurements show an upregulation of CDG1 and SSU1 gene expression levels in the wild type in the presence or absence of 5 mM cysteine after 6 h of growth in SD medium.