Microbial synthesis and properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) in Comamonas acidovorans

Comamonas acidovorans DS-17 was isolated from activated sludge and found to produce copolymers of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) at 30 degrees C under growth-limited conditions. When 1,4-butanediol or 4-hydroxybutyric acid was used as the sole carbon source, a P(4HB) homopolymer was produced. Random copolymers of 3HB and 4HB units were produced on the addition of glucose or 3-hydroxybutyric acid to the culture solution of 4-hydroxybutyric acid. The physical properties of P(3HB-co-4HB) copolyesters with high 4HB fractions (64-100 mol%) were investigated. The copolyester films with high 4HB fractions exhibited the characteristics of a thermoplastic elastomer, and the tensile strength increased from 17 to 104 MPa as the 4HB fraction was increased from 64 to 100 mol%. The biodegradabilities of P(3HB-co-4HB) films were studied in aqueous solutions of extracellular polyhydroxybutyrate (PHB) depolymerase from Alcaligenes faecalis or of lipase from Rhizopus delemer. The erosion rate of P(3HB-co-4HB) films by PHB depolymerase decreased as the 4HB fraction in copolyester was increased from 64 to 100 mol%. In contrast, the erosion rate of films by lipase increased with the 4HB fraction.