REPRESSION OF PHENOL CATABOLISM BY ORGANIC-ACIDS IN RALSTONIA-EUTROPHA

During batch growth of Ralstonia eutropha (previously named Alcaligene s eutrophus) on phenol in the presence of acetate, acetate was found t o be the preferred substrate; this organic acid was rapidly metabolize d, and the specific rate of phenol consumption was considerably decrea sed, although phenol consumption was not abolished. This decrease corr esponded to a drop in phenol hydroxylase and catechol-2,3-dioxygenase specific activities, and the synthesis of the latter was repressed at the transcriptional level, Studies with a mutant not able to consume a cetate indicated that the organic acid itself triggers the repression, Other organic acids were also found to repress phenol degradation. On e of these, benzoate, was found to completely block the catabolism of phenol (diauxic growth). A mutant unable to metabolize benzoate was al so unable to develop on benzoate-phenol mixtures, indicating that the organic acid rather than a metabolite involved in benzoate degradation was responsible for the repression observed.