Production and Characterization of Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) from L-Valine by Ralstonia eutropha

The biosynthesis of polyesters from different L-amino acids was investigated by wild-type Ralstonia eutropha (formerly Alcaligenes eutrophus). The accumulation and degradation of the polyesters was found to occur during the cultivation time from 6 h to 48 h, when R. eutropha was cultivated on nitrogen-poor medium containing 1% (w/v) of each L-amino acid as the sole carbon source by two-step batch fermentation. L-Valine was best among different L-amino acids used for the polyester productivity. The polyester content in dried cells produced from L-valine as the sole carbon source was up to 36 wt % during the cultivation time from 24 h to 36 h in a two-step fermentation and up to 27 wt % during 120 h of culture time in a one-step fermentation, respectively. The compositions and molecular weights of the polyesters produced from L-valine were ca. 90 mol% of 3-hydroxybutyric acid (3HB) and ca. 10 mol% of 3-hydroxyvaleric acid (3HV) units and up to 5 × 10^5-8 × 10^5 g mol^-1, respectively. As-biosynthesized P(3HB-co-ca. 10 mol% 3HV) was shown to have a random sequence distribution of 3HB and 3HV units by analysis of the 13C NMR spectra and have a very narrow comonomer compositional distribution by the fractionation method with chloroform/heptane mixed solvent.