Appl Environ Microbiol, January 1998, p. 1-6, Vol. 64, No. 1
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Centre de Bioingénierie Gilbert Durand, Unité Mixte de Recherche 5504 du Centre National de la Recherche Scientifique, Laboratoire associé à l'Institut National de Recherche Agronomique, Institut National des Sciences Appliquées, Complexe Scientifique de Rangueil, 31077 Toulouse Cedex 4, France
Received 11 August 1997/Accepted 4 October 1997
During batch growth of Ralstonia eutropha (previously named Alcaligenes eutrophus) on phenol in the presence of acetate, acetate was found to be the preferred substrate; this organic acid was rapidly metabolized, and the specific rate of phenol consumption was considerably decreased, although phenol consumption was not abolished. This decrease corresponded 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 acetate indicated that the organic acid itself triggers the repression. Other organic acids were also found to repress phenol degradation. One of these, benzoate, was found to completely block the catabolism of phenol (diauxic growth). A mutant unable to metabolize benzoate was also 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.
Present address: ORSTOM-Laboratoire de Biotechnologie et de
Microbiologie Tropicale, 34032 Montpellier Cedex 1, France.
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