Co-metabolic degradation of mixtures of monochlorophenols by phenol-degrading microorganisms

Two phenol-degrading organisms, Ralstonia eutropha TCP and a Pseudomonas aeruginosa strain, were studied for their co-metabolic capabilities towards chlorophenol (CP) isomers at different substitution grade. R. eutropha TCP resting cells, grown on different substrates, oxidised to varying degrees and regardless the growth substrate, some CP, while the dechlorinating activity/ies of the strain was/were repressed when grown on glutamate. 4MCP was co-metabolised via meta-fission of the aromatic nucleus with the formation of a product with the same spectrophotometric features of 5-chloro-2-hydroxymuconic semialdehyde. The co-metabotites of 2,6-dichlorophenol (2,6DCP) and 2,3,6-trichlorophenol (2,3,6TCP), not yet identified, are probably related to hydroxylated derivatives of the parent CP and/or their condensation products. The growth of R. eutropha TCP was differently affected by the presence of CPs depending on CP type and concentration. After an initial exposure to monochlorophenol (MCP) isomers at 10 mg l(-1) the strain succeeded in tolerating up to 30 mg l(-1) of 2MCP and 50 mg l(-1) of 3- and 4MCP. Viable counts, on comparison with those of other isomers, confirmed the highest toxicity of 2MCP towards R. eutropha TCP adapted cells. However, the organism was capable of totally degrading all the three MCPs, each at 10 mg l(-1), also in binary and ternary combinations in mixture with phenol (POH). P. aeruginosa totally degraded 3- and 4MCP, both singly and in mixture, when supplied at 25 mg l(-1). Differently from R. eutropha TCP, this strain did not cometabolise 2MCP which remained in the cultural broths without inhibiting microbial activities.