Biodegradation of poly(3-hydroxybutyrate)-derived polymers with different 4-hydroxybutyrate fractions by a novel depolymerase from Paecilomyces sp. 1407

Abstract A poly(3-hydroxybutyrate- co -4-hydroxybutyrate) [P(3HB- co -4HB)]-degrading strain was isolated and identified as Paecilomyces sp. A novel P(3HB- co -4HB) depolymerase with a molecular weight of 55 kDa was purified by column chromatography from the culture supernatant of the strain. The purified depolymerase showed optimum activity at pH 6.0 and 30 °C, and it was stabilized at pH 4.0–7.0 and below 40 °C. The depolymerase degraded poly(3-hydroxybutyrate) (PHB), poly(hydroxybutyrate- co -hydroxyvalerate), and several short-chain-length esters other than P(3HB- co -4HB) but showed no remarkable activity on poly(e-caprolactone) and poly(L-lactic acid). The main enzymatic products comprised hydroxybutyrate monomers, including 3HB and 4HB. The enzymatic erosion rate on the films increased markedly with increasing fraction of 4HB units. Enzymatic hydrolysis processes of PHB and P(3HB- co -4HB) were systematically analyzed in three aspects: enzyme adsorption, single-polymer-chain dissociation, and chemical linkage breakdown. Results indicate that 4HB insertion caused no effect on the degradation of solid-phase PHB-derived material at the molecular chain level but affected enzyme adsorption and crystallinity of the materials. Hindering single-chain stripping by crystallinity dominantly affects the degradation behavior of the polymer.