Enzymatic degradation of poly(hydroxyalkanoates) by Pseudomonas pickettii

A bacterium capable of degrading poly(3-hydroxybutyrate) [P(3HB)] was isolated from laboratory media and identified as Pseudomonas pickettii. The strain P. pickettii excreted an extracellular poly(hydroxyalkanoate) (PHA) depolymerase and grew on P(3HB) as the sole carbon source. P. pickettii also grew on 3-hydroxybutyrate, glucose, fructose, citrate or succinate. However, only 3-hydroxybutyrate apart from P(3HB) induced the secretion of PHA depolymerase. The PHA depolymerase was purified from the culture medium containing 3-hydroxybutyrate at the sole carbon source by hydrophobic column chromatography and gel filtration, and its molecular weight was determined as about 40,000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The optimum activity of degrading P(3HB) by the depolymerase was observed at pH 5.5 and 40 degrees C. The enzymatic degradation of microbial copolyesters was studied by the weight loss (erosion) of solution-cast films of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate). 1H-n.m.r. analysis of the water-soluble products after the hydrolysis of P(3HB) film by PHA depolymerase revealed that the main product was the monomer 3-hydroxybutyric acid.