Effect of inactivation of poly(hydroxyalkanoates) depolymerase gene on the properties of poly(hydroxyalkanoates) in Pseudomonas resinovorans
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- Solaiman, D.K.Y., Ashby, R.D. & Foglia, T.A. Appl Microbiol Biotechnol (2003) 62: 536. doi:10.1007/s00253-003-1317-4
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The phaZ gene of Pseudomonas resinovorans codes for a poly(hydroxyalkanoates) (PHA) depolymerase. Two phaZ mutants of Pseudomonas resinovorans NRRL B-2649, FOAC001 and FOAC002, were constructed by an in vitro transposition procedure followed by chromosomal integration via homologous recombination. A detailed mapping of the transposon insertion sites and an analysis of the resultant sequences showed that putative fusion polypeptides PhaZFOAC001 (239 amino-acid residues) and PhaZFOAC002 (85 amino-acid residues) could result from the mutant phaZ genes of FOAC001 and FOAC002, respectively. In vivo PHA degradation data indicated that PhaZFOAC001 might still retain a partial PHA depolymerization activity, while PhaZFOAC002 is completely devoid of this function. The cell yields and PHA contents of B-2649, FOAC001, and FOAC002 were similar when the cells were grown either under a limiting nitrogen-source (low-N) condition for up to 5 days or in excess N-source (high-N) for 3 days. A dramatic decrease in PHA content was observed in the PhaZ-active B-2649 and FOAC001 cells during prolonged cell growth (5 days) in high-N medium or in response to a shift-up in nitrogen-source. The repeat-unit compositions of the PHAs from FOAC001 and FOAC002 contained slightly lower amounts of β-hydroxyoctanoate and higher β-hydroxytetradecenoate than that of the wild-type B-2649 when grown under a high-N condition. While the molecular masses of the PHAs from FOAC001 and FOAC002 did not vary under any conditions used in this study, those of the wild-type B-2649 were markedly increased in cells either grown for 5 days under a high-N condition or subjected to a nitrogen-source shift-up. These phaZ mutants thus provide a valuable system to study the influence of PHA depolymerase on the accumulation and properties of medium-chain-length PHA.