[Adaptation of Candida tropicalis yeasts to increasing hydroquinone concentrations]

The optimal concentration of hydroquinone in the Rieder medium for Candida tropicalis is 0.2 to 0.25%. This yeast is capable of growing in a medium containing up to 0.7-0.9% of hydroquinone. C. tropicalis cultures capable of growing in the Rieder medium containing 2.5% of hydroquinone have been obtained by the method of experimental adaptation. Comparative studies of yeast cultures adapted to 0.5 and 1.5% of hydroquinone have shown that the lag period in the batch culture decreases noticeably as the result of adaptation. The coloured products of hydroquinone transformation are not accumulated any more in the cultural broth and the cells. The generation time of the yeast is the same during cultivation on 0.2 and 0.5% hydroquinone but differs if the content of hydroquinone in the medium is 1%. No increase in the economic coefficient has been found during cultivation of the yeast cultures adapted to 1.5% hydroquinone in media containing 0.2 and 0.5% of hydroquinone, although the activity of phenol monooxygenase increased. The latter peculiarity of the adapted cultures was most pronounced during cultivation in media containing 0.5 to 1% of hydroquinone. No changes have been detected in the regulation mechanisms for biosynthesis of phenol monooxygenase or in the resistance of the enzyme to the substrate and the products of its spontaneous oxidation.