Biosynthesis and characterization of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) in Alcaligenes eutrophus

Abstract

Copolyesters of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) were produced by Alcaligenes eutrophus at 30°C in nitrogen-free culture solutions containing γ-butyrolactone alone or with fructose or butyric acid as the carbon sources. When γ-butyrolactone was used as the sole carbon source, the 4HB fraction in copolyester increased from 9 to 21 mol% as the concentration of γ-butyrolactone in the culture solution increased from 10–25 g/l. The addition of fructose to the culture solution of y-butyrolactone resulted in a decrease in the 4HB fraction in copolyester. The copolyesters produced from γ-butyrolactone and fructose by A. eutrophus were shown to have a random sequence distribution of 3HB and 4HB units by analysis of the 125 MHz 13C n.m.r. spectra. In contrast, a mixture of random copolyesters with two different 4HB fractions was produced by A. eutrophus when γ-butyrolactone and butyric acid were used as the carbon sources. These results are discussed on the basis of a proposed biosynthetic pathway of P(3HB-co-4HB). The copolyester films became soft with an increase in the 4HB fraction, and the elongation to break at 23°C increased from 5 to 444% as the 4HB fraction increased from 0 to 16 mol%. The P(3HB-co-10%4HB) film was shown to be biodegradable in an activated sludge.