In Pseudomonas putida U, the degradation of n-alkanoic and n-phenylalkanoic acids is carried out by two sets of β-oxidation enzymes (βI and βII). Whereas the first one (called βI) is constitutive and catalyses the degradation of n-alkanoic and n-phenylalkanoic acids very efficiently, the other one (βII), which is only expressed when some of the genes encoding βI enzymes are mutated, catabolizes n-phenylalkanoates (n > 4) much more slowly. Genetic studies revealed that disruption or deletion of some of the βI genes handicaps the growth of P. putida U in media containing n-alkanoic or n-phenylalkanoic acids with an acyl moiety longer than C4. However, all these mutants regained their ability to grow in media containing n-alkanoates as a result of the induction of βII, but they were still unable to catabolize n-phenylalkanoates completely, as the βI-FadBA enzymes are essential for the β-oxidation of certain n-phenylalkanoyl-CoA derivatives when they reach a critical size. Owing to the existence of the βII system, mutants lacking βI-fadB/A are able to synthesize new poly 3-OH-n-alkanoates (PHAs) and poly 3-OH-n-phenylalkanoates (PHPhAs) efficiently. However, they are unable to degrade these polymers, becoming bioplastic overproducer mutants. The genetic and biochemical importance of these results is reported and discussed.
ASJC Scopus subject areas
- Molecular Biology