Induction of phenol assimilation in chemostat cultures of Candida maltosa L4

Abstract To investigate the induction of phenol hydroxylase and catechol 1,2‐dioxygenase in Candida maltosa L4 during chemostat cultivation, changes in the growth‐limiting substrate were carried out at different dilution rates. No activity of phenol hydroxylase and catechol 1,2‐dioxygenase could be detected in the cells during chemostat cultivation of C. maltosa L4 under glucose limitation independent of the dilution rate. However, once the feed line was changed from glucose medium ( s r = 28 mM) to a medium containing either phenol ( s r = 28 mM) or a mixture of phenol ( s r = 18 mM) and glucose ( s r = 10 mM), both the phenol hydroxylase and the catechol 1,2‐dioxygenase were fully induced. After 5 hours at all dilution rates tested ( D = 0.05 h −1 , D = 0.11 h −1 , and D = 0.2 h −1 ). In spite of this enzyme synthesis, the cells were washed out if C. maltosa L4 was shifted from glucose to phenol at a higher dilution rate than D = 0.05 h −1 , probably due to accumulation of inhibiting concentrations of phenol in the medium and starvation of NADPH. If being shifted from glucose to a mixture of phenol and glucose, however, the cells reached a new steady state even at a higher dilution rate of D = 0.2 h −1 . The specific activity of phenol hydroxylase in crude extracts of C. maltosa L4 was nearly independent of the growth rate in the range D = 0.05 h −1 to D = 0.2 h −1 on both phenol and a mixture of phenol and glucose, respectively, as the growth‐limiting substrates. In contrast, catechol 1,2‐dioxygenase activity correlated with the growth rate when the cells were cultivated on phenol. In the presence of mixtures of phenol and glucose, the observed decrease of specific activity of this enzyme at a high dilution rate ( D = 0.2 h −1 ) is possibly a result of repression by glucose or an glucose metabolite.