Degradation of 4-Chlorophenol via the meta Cleavage Pathway by Comamonas testosteroni JH5

Abstract

Comamonas testosteroni JH5 used 4-chlorophenol (4-CP) as its sole source of energy and carbon up to a concentration of 1.8 mM, accompanied by the stoichiometric release of chloride. The degradation of 4-CP mixed with the isomeric 2-CP by resting cells led to the accumulation of 3-chlorocatechol (3-CC), which inactivated the catechol 2,3-dioxygenase. As a result, further 4-CP breakdown was inhibited and 4-CC accumulated as a metabolite. In the crude extract of 4-CP-grown cells, catechol 1,2-dioxygenase and muconate cycloisomerase activities were not detected, whereas the activities of catechol 2,3-dioxygenase, 2-hydroxymuconic semialdehyde dehydrogenase, 2-hydroxymuconic semialdehyde hydrolase, and 2-oxopent-4-enoate hydratase were detected. These enzymes of the meta cleavage pathway showed activity with 4-CC and with 5-chloro-2hydroxymuconic semialdehyde. The activities of the dioxygenase and semialdehyde dehydrogenase were constitutive. Two key metabolites of the meta cleavage pathway, the meta cleavage product (5-chloro-2-hydroxymuconic semialdehyde) and 5-chloro-2-hydroxymuconic acid, were detected. Thus, our previous postulation that C. testosteroni JH5 uses the meta cleavage pathway for the complete mineralization of 4-CP was confirmed. The aerobic microbial degradation of many aromatic compounds occurs via catechols as key metabolites. The breakdown of catechols proceeds via the central step of ortho or meta ring fission. In general, methyl-substituted aromatic compounds are degraded via the meta cleavage pathway, whereas xenobiotics like chloroaromatic compounds are mineralized via the ortho cleavage pathway (9, 21). The degradation of methyl-and chloroaromatic substrates in mixture is often incomplete, leading to the accumulation of dead-end metabolites like chlorocatechols, chlorinated hydroxymuconic semialdehydes, or 4-carboxymethyl-methylbut-2-en-1,4-olides (31, 33). As a possible metabolite of chloroaromatic breakdown, 3-chlorocatechol (3-CC) reversibly inhibits the meta-cleaving catechol 2,3-dioxygenase or totally blocks the meta cleavage pathway by the irreversible suicide inactivation of this dioxygenase (4, 16, 20). Recently, we described Comamonas testosteroni JH5, which completely mineralizes a mixture consisting of 4-chlorophenol (4-CP) and monomethylphenols (16). The degradation of 4methylphenol (4-MP) and 4-CP occurred successively. Mixtures consisting of 4-CP and 2-MP or 3-MP were mineralized simultaneously. Since a catechol 2,3-dioxygenase, but no orthocleaving enzyme, was detected in cells grown on 4-CP, the mineralization of 4-CP via meta ring fission was postulated (16). Furthermore, a Pseudomonas species is able to completely mineralize 5-chlorovanillate via meta cleavage (18). Kersten et al. (18) showed that the formed acylchloride undergoes cyclization, which leads to a spontaneous removal of the chloride substituent. This mechanism is restricted to orthosubstituted halogens and therefore would not work with 4-CP. Recently, the meta cleavage of 4-chlorobenzoate by Pseudomonas cepacia ...

A GAC biofilm reactor for the continuous degradation of 4-chlorophenol: treatment efficiency and microbial analysis

“…In addition, this may indicate that typical degrading laboratory species may fail to implant successfully within treatment populations, compared to bacterial communities established naturally in biofilms. The degradation of 4-CP by single species has also been reported by other authors (Bae et al 1996;Kafkewitz et al 1996;Hollender et al 1997;Finkel'shtein et al 2000).…”

“…Chloroaromatic compounds are susceptible to biodegradation, and aerobic degradation often involves their mineralization to innocuous products, thereby making the utilization of these reactions especially attractive in remediation applications. It has been reported that 4-chlorophenol (4-CP) can be partially or completely degraded aerobically by several bacteria including Pseudomonas (Knackmuss and Hellwig 1978), Azotobacter (Wieser et al 1994), Alcaligenes (Hill et al 1996), and Rhodococcus (Finkel'shtein et al 2000), and via different biodegradation pathways (Bae et al 1996;Hollender et al 1997).…”

Effect of biogenic substrate concentration on chlorophenol degradation kinetics

“…Then 3,5‐dichlorocatechol is converted to 2,4‐dichloro‐ cis,cis ‐muconate, which is catalysed by 3,5‐dichlorocatechol 1,2‐dioxygenase 28. It was reported that phenol hydroxylase has broad substrate specificity and can also catalyse the turnover of 2,4‐DCP 29. It is also known that 2,4‐dichlorophenol hydroxylase can convert 4‐CP to 4‐chlorocatechol 30.…”

Quantification of catechol dioxygenase gene expression in soil during degradation of 2,4-dichlorophenol

“…GP1, Comamonas testosteroni JH5 and BRC60 Sphingomonas putida GJ31 and Sphingomonas sp. BN6 have been isolated that transform chlorophenols via meta cleavage (Nakatsu & Wyndham, 1993;Wieser et al, 1994;Hollender et al, 1997;Koh et al, 1997;Kaschabek et al, 1998;Riegert et al, 1998;Mars et al, 1999). Environmentally, it remains unclear which of these pathways (ortho or meta) is used during in situ degradation.…”