Reversible accumulation of p-hydroxybenzoate and catechol determines the sequential decomposition of phenolic compounds in mixed substrate cultivations in pseudomonads

Accumulation of key catabolic intermediates during degradation of phenol, p -cresol and benzoate was studied in two-substrate batch cultivations by the strains Pseudomonas mendocina PC1, Pseudomonas fluorescens PC18 and P. flu orescens PC24. According to sequence analysis of 16S rRNA genes the strains belonged to different monophyletic clusters of Pseudomonas. The catechol 2 ,3-dioxygenase (C23O) gene, xylE, of strain PC1 and the phenol monooxygenas e gene, pheA, of PC24 were localised on the chromosome, while the C23O gene , xylE, of strain PC18 and the p-cresol methylhydroxylase gene, pchF, of st rains PC18 and PC24 were on plasmids. It was shown that, if the substrates were degraded from mixtures using either catechol meta, catechol ortho or c atechol ortho and protocatechuate ortho pathways, then both substrates were catabolised simultaneously (nondiauxic growth) without the accumulation of intermediates. Exceptionally, degradation of phenol and benzoate via the c atechol ortho pathway caused irreversible accumulation of eis,cis-muconate without detectable effect on simultaneous consumption of substrates. When t he substrates were degraded from mixtures through meta and ortho catabolic pathways, the sequential consumption of substrates (diauxic growth) was obs erved due to the reversible accumulation of the catabolic intermediates p-h ydroxybenzoate or catechol. Regulation of parallel catabolic pathways by th e accumulation of catabolic intermediates depended on the concentration of growth substrates. At low concentrations simultaneous degradation occurred and the antagonistic effect of p-hydroxybenzoate on the degradation of phen ol was diminished. In strain PC18 only the accumulation of P-hydroxybenzoat e during growth on a phenol-p-cresol mixture seems to be directly metabolic ally regulated because phenol also induces the catabolic pathway for p-cres ol degradation. Partial sequencing of the pchF genes of strains PC18 and PC 24 showed considerable differences. (C) 2001 Federation of European Microbi ological Societies. Published by Elsevier Science B.V. All rights reserved.