Biodegradation of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by a novel P3/4HB depolymerase purified from Agrobacterium sp. DSGZ

A poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3/4HB)-degrading strain, Agrobacterium sp. DSGZ, was isolated from sewage by poly(3-hydroxybutyrate) (PHB) mineral agar plates. A novel P3/4HB depolymerase with a molecular weight of 34 kDa was purified through a novel single-step affinity chromatography method from the culture supernatant of the strain by using P3/4HB powder as a substrate. The purified depolymerase showed optimum activity at pH 7.0 and 50°C, and was stable at the pH range of 6.0 to 9.0 and temperature below 50°C. Enzyme activity was strongly inhibited by phenylmethylsulfonyl fluoride (PMSF), ethylenediaminetetraacetic acid (EDTA), hydrophobic reagents, and some metal ions. The depolymerase degraded poly(3-hydroxybutyrate) (PHB), poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV), P3/4HB, and polycaprolactone (PCL), instead of polylactic acid (PLA) or poly(butylene succinate) (PBS). Meanwhile, the depolymerase showed high hydrolytic activity against short-chain length esters, such as butyrate acid ester and caprylic acid ester. The main degradation products of the depolymerase were identified as hydroxybutyrate monomers and dimers, and the monomers were identified as 3-hydroxybutyrate (3HB) monomers and 4-hydroxybutyrate (4HB) monomers. The preparation procedure, crystallinity, and 4HB composition of the P3/4HB copolymer showed evident effect on degradation behavior, and change in crystallinity was the main factor affecting degradation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42805.