Two different pathways are involved in the β-oxidation of n-alkanoic and n-phenylalkanoic acids in Pseudomonas putida U:: genetic studies and biotechnological applications

In Pseudomonas putida U, the degradation of rr alkanoic and n-phenylalkanoic acids is carried out by two sets of beta -oxidation enzymes (beta (I) and beta (II)) Whereas the first one (called beta (I)) is constitutive and catalyses the degradation of n-alkanoic and n-phenylalkanoic acids very efficiently, the other one (beta (II)), which is only expressed when some of the genes encoding beta (I) enzymes are mutated, catabolizes n-phenylalkanoates (n > 4) much more slowly. Genetic studies revealed that disruption or deletion of some of the beta (I) genes handicaps the growth of P. putida U in media containing n-alkanoic or n-phenylalkanoic acids with an acyl moiety longer than C-4. However, all these mutants regained their ability to grow in media containing n-alkanoates as a result of the induction of beta (II), but they were still unable to catabolize n-phenylalkanoates completely, as the beta (1)-FadBA enzymes are essential for the beta -oxidation of certain n-phenylalkanoyl-CoA derivatives when they reach a critical size. Owing to the existence of the beta (II) system, mutants lacking beta (1)-fadB/A are able to synthesize new poly 3-OH-n-alkanoates (PHAs) end poly 3-OH-n-phenylalkanoates (PHPhAs) efficiently, However, they are tenable to degrade these polymers, becoming bioplastic overproducer mutants. The genetic and biochemical importance of these results is reported and discussed.