Fig. 7

Proposed pathway for PHA production associated with biphenyl degradation. The biodegradation pathway for biphenyl (shown to the left) has already been described (Brenner et al. 1994). HOPDA, 2-hydroxy-6-oxo-phenylhexa-2,4-dienoate, is degraded to HPDA, 2-hydroxypenta-2,4-dienoate, and benzoate. HPDA is metabolized to pyruvate and acetyl-CoA, and the pyruvate is further converted to acetyl-CoA through common cellular functions such as that by pyruvate dehydrogenase. Acetyl-CoAs generated here would be used to produce polyhydroxybutyrate (PHB) via β-ketothiolase (encoded by phaA), NADPH-dependent reductase (encoded by phaB), and PHA synthase (encoded by phaC1). As for the generation of 3HV-CoA, it can be speculated that a possible sequential conversion from succinyl-CoA to methylmalonyl-CoA, and consequently to propionyl-CoA, would be carried out by the intracellular metabolism. Finally, 3HV-CoA would be generated by the condensation of propionyl-CoA with acetyl-CoA. Accordingly, copolymer P(3HB-co-3HV) can be biosynthesized by the copolymerization of two molecules, 3HB-CoA and 3HV-CoA