Ring Fission by 2,3-Dihydroxybiphenyl Dioxygenase

The next step in degradation involves hydrolysis of 2-hydroxy-6-keto-6-phenylhexa-2, 4-dienoate to benzoate and 2-hydroxy-penta-2,4-dienoate encoded by the hydrolase BphD. 

FIGURE 9.6 Aerobic degradation of (a) biphenyl by biphenyl-2,3-dioxygenase, (b) a polychlorinated 4 -chlorobiphenyl. 

Collectively, these conclusions are supported by the results of a study of 33 congeners using Acinetobacter sp. strain P6 (Rhodococcus globerulus) (Asturias and Timmis 1993). The extradiol 

A rearrangement (NIH shift) occurred during the transformation of 2-chlorobiphenyl to 2-hydroxy-3-chlorobiphenyl by a methanotroph, and is consistent with the formation of an intermediate arene oxide (Adriaens 1994). The occurrence of such intermediates also offers plausible mechanisms for the formation of nitro-containing metabolites that have been observed in the degradation of 4-chlo-robiphenyl in the presence of nitrate (Sylvestre et al. 1982). 

Apart from induction of degradative enzymes by growth with biphenyl, nonrelated naturally occurring substrates have been shown to induce the enzymes for PCB degradation. 

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