Glucose repression and derepression play a central role in regulating carbon source utilization in yeasts. However, the strength and dynamics of this regulation differ markedly among yeast species. In this study, invertase regulation was examined under short- and long-term derepression in several non-conventional yeasts (Pichia farinosa, Pichia anomala, Pichia jadinii and Candida milleri). Saccharomyces cerevisiae was included as a reference yeast species. Yeast cells were first grown under fermentable and nonfermentable conditions to establish short-term and long-term derepressed metabolic states, and subsequently transferred to repressed (2% glucose) or derepressed (0.05% glucose) media prior to invertase activity measurements. Growth analysis revealed clear interspecies differences in metabolic performance. Non-conventional yeasts, particularly P. jadinii, maintained relatively high growth rates under both rich and minimal conditions. Invertase activity showed distinct regulatory patterns among species. S. cerevisiae displayed strong glucose-dependent repression and robust induction under derepressed conditions, as expected. In contrast, P. farinosa exhibited no detectable invertase activity. P. anomala showed a transient increase in activity during short-term derepression, but this response was not sustained after long-term derepression. P. jadinii exhibited high and persistent invertase activity, especially following long-term derepression. C. milleri maintained elevated invertase activity under both repressed and derepressed conditions, indicating reduced sensitivity to glucose availability. Time-course experiments demonstrated that invertase regulation is highly dynamic and strongly influenced by prior growth conditions. Overall, these findings highlight the diversity of carbon regulation strategies in yeasts and emphasize the metabolic flexibility of non-conventional yeast species.
Tülay TURGUT GENÇ (Wed,) studied this question.