Fig. 1.

Growth (a) and riboflavin productivity (b) of P. guilliermondii WT and Δyfh1 mutant in synthetic sulfur free medium B supplemented with different sulfur containing compounds. Cultures of P. guilliermondii wild-type strain R-66 (WT) and Δyfh1 mutant were grown aerobically in YPS medium for 16 h. Cells were pelleted, washed with water and resuspended in water to an optical density OD₆₀₀ of 0.2. Aliquots of 0.3 ml were inoculated in 100 ml Erlenmeyer flasks containing 20 ml of the synthetic medium B containing 3.6 μM of iron added as ammonium ferrous sulfate and supplemented with: (NH4)₂SO₄—40 mM of ammonium sulfate, Na₂SO₃—2.5 mM of sodium sulfite, Met—0.2 mM of methionine, GSH—0.2 mM of glutathione, Cys—0.2 mM of cysteine, NACys—0.1 mM N-Acetyl-L-cysteine, Na₂S—5 mM sodium sulfide. Cell density and concentration of riboflavin were determined after 5 days of incubation at 30°C on gyro shaker at 200 rpm. Values are means ± SE of three independent experiments