The inhibitory effect and substrate properties of benzoic acid were estimated for 25 yeast strains belonging to genera Candida, Hansenula, Hypopichia, Rhodosporidium, Rhodotorula, Saitoella and Trichosporon. Benzoic acid can serve as a sole carbon source for growth of yeasts belong to genera Rhodotorula, Rhodosporidium and Saitoella in synthetic mineral media. Specific growth rate is strongly dependent both on the concentration of benzoate and the pH value of the cultivation media. Maximum specific growth rate on benzoate is observed in alkaline cultivation media at pH 7.0-7.5 whereas those for growth on glucose in mildly acidic media at pH 5.0. Some of the strains showed weak growth on benzoate even at pH 8.5. Some carotenoid-containing yeasts of the genera Rhodotorula and Rhodosporidium lost their ability to synthesize carotenoid pigments during growth in alkaline benzoate media.
Xylose or glucose (≤5 g/l) was utilized simultaneously with benzoate (5 g/l) byRhodosporidium toruloides andRhodotorula rubra in batch culture. At a higher glucose concentration, benzoate was utilized only after glucose was depleted from the media. Both yeasts preferentially utilized benzoate before xylose even if there were more than 5 g xylose/l.Rhodotorula glutinis preferentially utilized glucose (≤10 g/l) before benzoate but utilized xylose and benzoate simultaneously.
The appearance of cytochrome content in the yeast Rhodosporidium toruloides depended on the substrate supporting growth. The cells of R. toruloides growing on benzoate were found to contain cytochrome P‐450. The concentration of cytochrome P‐450 was maximal at the beginning of the exponential phase and then remained at a relatively constant level, but rapidly decreased at the beginning of the stationary phase. When benzoate was exhausted from the medium, the cytochrome P‐450 level decreased to zero. On the other hand, cytochrome P‐450 was not detected when R. toruloides grew on glucose. However, cytochrome P‐450 was detected, when R. toruloides was grown on benzoate together with glucose.
The maximal content of cytochrome c in the cells was observed at the beginning of the exponential phase of growth on both substrates and decreased most rapidly during late stationary phase of growth. The content of cytochrome c in R. toruloides was 2–3 times lower during the growth on glucose as compared to the growth on benzoate.
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