Enzymatic degradation of poly[( R)-3-hydroxybutyrate] by Comamonas testosteroni ATSU of soil bacterium

Abstract

A bacterium capable of degrading poly(3-hydroxybutyrate) (P(3HB)) was isolated from the soil and identified as Comamonas testosteroni. The strain C.testosteroni ATSU excreted an extracellular PHB depolymerase and grew on P(3HB) as a sole carbon source. C.testosteroni also grew on 3-hydroxybutyrate P(3HB), malate, and poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (P(3HB- co-3HV)). The secretion of PHB depolymerase was induced in the presence of P(3HB) and P(3HB- co-3HV). The PHB depolymerase was purified to electrophoretic homogeneity from the culture medium by hydrophobic column chromatography, preparative isoelectric focusing and gel filtration, and its molecular weight was determined as 49 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The optimum activity of degrading P(3HB) by the depolymerase was observed at pH 8·5 and 70°C. The enzymatic hydrolysis of P(3HB) film produced water-soluble products composed of the monomer and dimer of 3-hydroxybutyric acid. The rate of production of the monomer and dimer increased to a maximum value with the concentration of PHB depolymerases, followed by a gradual decrease. The properties of PHB depolymerase from C.testosteroni ATSU were compared with those of PHB depolymerase from Alcaligenes faecalis TI, Pseudomonas pickettii YM-b and Comamonas testosteroni YM1004.