Cooxidation of chloro- and methylphenols by Alcaligenes xylosoxidans JH1

Alcaligenes xylosoxidans subspecies denitrificans JH1 was enriched with 2-c hlorophenol from a mixed culture degrading different chloro- and methylphen ols. The strain used all monochloro- and monomethylphenols apart from 2-met hylphenol as sole source of energy and carbon with stoichiometric release o f chloride. 4-Chlorophenol was mineralized up to a concentration of 1.3 mM. Degradation of mixtures of monochloro- and monomethylphenols occurred at l east partially except for the mixture of 2-chlorophenol and 3-methylphenol. Depending upon the growth substrates used, enzymes of the ortho and/or met a cleavage pathway catalysed the degradation of the phenols. The transforma tion of chlorophenols was concluded to occur exclusively via the ortho clea vage pathway because no chlorocatechol 2,3-dioxygenase activity was found i n chlorophenol-grown cells. Degradation of 4-methylphenol in strain JH1 occ urred both by the ortho and meta cleavage pathway as indicated by the findi ng that the ortho- and meta-cleaving dioxygenases were expressed in 4-methy lphenol-grown cells. Transformation of methylphenols by the ortho cleavage pathway led to the accumulation of methyllactones as dead-end products. Mix tures of methyl- and chlorophenols were metabolized mainly by the ortho cle avage pathway because chlorocatechols formed inactivated the constitutive c atechol 2,3-dioxygenase which caused channelling of methylphenols into the ortho cleavage pathway.