Phenanthrene degradation pathways

Adachi K, T Iwabuchi, H Sano, S Harayama (1999) Structure of the ring cleavage product of l-hydroxy-2-naphthoate, an intermediate of the phenanthrene-degradative pathway of Nocardioides sp. strain KP7. J Bacterial 181 757-763. 

The degradation of these was described many years ago (Evans et al. 1965), and details have since been added (Figure 8.10a) (van Herwijnen et al. 2003). Phenanthrene is more readily degraded than anthracene, and both can be degraded to o-phthalate. After hssion of the peripheral ring in phenanthrene, several pathways have been demonstrated ... 

Carbazole, A-methylcarbazole, IV-ethylcarbazole, dibenzofuran, dibenzothiophene, fluorene, dibenzo-p-dioxin, phenoxathiin, phenoxazine, phenothiazine, xanthene, biphenyl, naphthalene, phenanthrene, anthracene, and fluoranthene could be transformed by E. coli, [314] which was transformed using a plasmid bearing the carAa, Ac, and Ad genes, and expressing only the carA-encoded proteins. Further work is needed to develop a final biocatalyst and to prove the advantages that this degradative pathway would incorporate in a refining bioprocess. 

C has been used as a tracer in the study of the degradation of [1-13C]-acenaphthene both in pure cultures that were degrading naphthalene and phenanthrene by cometabolism, and in a mixed culture that was enriched with creosote (Selifonov et al. 1998). The degradation pathway that is initiated by benzylic monooxygenation could be determined by isolation of intermediate metabolites, and the method proved applicable to the situation where only limited biotransformation of the substrates takes place by partial oxidation. 

The degradation pathways of higher molecular weight PAHs—such as pyrene, benzo(e)pyrene, and benzo(a)pyrene—are less well understood (Neilson and Allard, 1998). Because these compounds are more resistant to microbial degradation processes, they tend to persist longer in contaminated environments (Van Bmmmelen et al., 1998 Neilson and Allard, 1998 Bosma et al., 2001). However, the degradation of fluoranthene, pyrene, benz(a)anthracene, benzo(a)-pyrene, benzo(b)fluorene, chrysene, and benzo(b)fluoranthene has been reported in laboratory conditions (Barnsley, 1975 Mueller et al., 1988,1990 Schneider a/., 1996 Ye etal., 1996 Neilson and Allard, 1998). Elevated temperatures increase the rate of biotransformation reactions in vitro. For example, laboratory studies have shown a 50% loss of phenanthrene after 180 d at 8 °C in water compared to 75% loss in 28 d at 25 °C (Sherrill and Sayler, 1981 Lee etal., 1981). It is widely believed that PAHs with three or more condensed rings tend not to act as sole... 

The most common degradative pathway is through quatemization of the basic nitrogen followed by Hofmann elimination to furnish a phenanthrene possessing a i3-dimethylaminoethyl side chain. Such a phenanthrene alkaloid can then suffer... 

FIGURE 8.10 Degradation of (a) anthracene, (b,c) alternative pathways for phenanthrene. 

If PAH-degrading microorganisms use broad-specificity enzymes or common pathways to transform multiple PAHs, then inducers for the metabolism of one PAH substrate might co-induce the transformation of a range of PAHs. Preliminary evidence indicated that the transformation of naphthalene, phenanthrene, fluoranthene, and pyrene by Pseudomonas saccharophila P15 was stimulated by salicylate [132], a known inducer of naphthalene metabolism in pseudomonads [43]. However, Chen and Aitken [181] reported in more detail the inducing effects of salicylate on the transformation of various HMW PAHs by Pseudomonas saccharophila P15 isolated from contaminated soil, including... 

Retene is a methyl isopropyl phenanthrene (Fig. 2). As mentioned above, Wakeham [43] was the first to address the natural non-combustion production of retene in relation to lake sediments. The starting material for retene is abietic acid, a diterpenoid found primarily in the resin of coniferous trees. When burned, the abietic acid forms retene. It can also degrade via one of two pathways to retene without combustion (Fig. 5). One pathway is through dehydro abietin and another intermediate to retene. The other proceeds through dehydroabietane, another intermediate to simonellite and finally to retene. These mechanisms can occur in both the atmosphere [44] and in aquatic systems. Therefore, where there is abietic acid, retene can follow. This becomes especially important in areas where there are high densities of conifers, and thus abietic acid. 

Phenanthrene is more readily degraded than anthracene, and two different pathways are followed after cleavage of the peripheral ring in one, the naphthalene pathway via salicylate is used (Evans et al. 1965), whereas in the other o-phthalate and 3,4-dihydroxybenzoate are involved (Kiyohara et al. 1976 Kiyohara and Nagao 1978 Barnsley 1983) (Figure 6.38). The enzymes involved, l-hydroxy-2-naphthoate dioxygenase (Iwabuchi and Harayama... 

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