Effective biosynthesis of poly(3‐hydoxy‐ butyrate‐ co ‐4‐hydroxybutyrate) with high 4‐hydroxybutyrate fractions by Wautersia eutropha in the presence of α‐amino acids

BACKGROUND: Biopolymers produced by microbes are in demand as their biodegradable and biocompatible properties make them suitable for disposable products and for potential use as biomaterials for medical applications. The effective microbial production of copolyesters of 3‐hydroxybutyrate (3HB) and 4‐hydroxybutyrate(4HB) with high molar fractions of 4HB unit by a wild‐type Wautersia eutropha H16 was investigated in culture media containing 4‐hydroxybutyric acid (4HBA) and different carbon substrates in the presence of various α‐amino acids. RESULTS: The addition of carbon sources such as glucose, fructose and acetic acid to the culture medium containing 4HBA in the presence of α‐amino acids resulted in the production of random poly(3HB‐ co ‐4HB) with compositions of up to 77 mol% 4HB unit, but the yields of copolyesters with 60–77 mol% 4HB units were less than 15 wt% of dried cell weights. In contrast, when carbon sources such as propionic acid and butyric acid were used as the co‐substrates of 4HBA in the presence of α‐amino acids, poly(3HB‐ co ‐4HB) copolyesters with compositions of 72–86 mol% 4HB were produced at maximally 47.2 wt% of dried cell weight (11.3 g L −1 ) and the molar conversion yield of 4HBA to 4HB fraction in copolyesters was as high as 31.4 mol%. Further, poly(3HB‐ co ‐4HB) copolyesters with compositions of 93–96 mol% 4HB were isolated at up to 35.2 wt% of dried cell weights by fractionation of the above copolymers with chloroform/n‐hexane. CONCLUSION: The productivity of copolyesters with over 80 mol% 4HB fractions was as high as 0.146 g L −1 h −1 (3.51 g L −1 for 24 h) by flask batch cultivation. Copyright © 2007 Society of Chemical Industry