Effective microbial production of poly(4-hydroxybutyrate) homopolymer byRalstonia eutropha H16

Abstract

The effective microbial production of copolyesters of 3‐hydroxybutyrate (3HB) and 4‐hydroxybutyrate (4HB) with high mole fractions of 4HB units by a wild‐type strain of Ralstonia eutropha H16 was investigated in culture solutions containing 4‐hydroxybutyric acid (4HBA) and various carbon substrates in the presence of a nitrogen source such as ammonium sulfate. The addition of glucose or acetic acid to the culture solution containing 4HBA in the presence of ammonium sulfate resulted in the production of random copolymers of P(3HB‐co‐4HB) with compositions of up to 82 mol% 4HB, but the yield of copolymers was less than 7 wt% of dried cell weights. In contrast, when n‐alkanoic acids such as propionic acid, butyric acid, valeric acid and hexanoic acid, being subject to β‐oxidation metabolism in the cell, were used as the co‐substrates of 4HBA in the presence of ammonium sulfate, a mixture of copolymers with two different 4HB compositions was produced, and copolyesters with compositions of 93–100 mol% 4HB were isolated from chloroform–n‐hexane insoluble fractions in the mixture of copolymers. Especially, when this wild‐type Ralstonia eutropha H16 was cultivated in a medium containing 4HBA (15 g litre−1), propionic acid (5 g litre−1) and ammonium sulfate (5 g litre−1), namely C/N (mol/mol) = 10, the P(4HB) homopolymer was produced at maximally 34 wt% of dry cell weight (7.8 g litre−1), and the conversion yield of 4HBA to P(4HB) homopolymer resulted in values as high as 21 mol%. © 1999 Society of Chemical Industry

Characterization of new isolated Ralstonia eutropha strain A-04 and kinetic study of biodegradable copolyester poly(3-hydroxybutyrate-co-4-hydroxybutyrate) production

“…When C/N ratio decreased, which means that ammonium sulfate was oversupplied, the mole flux of acetyl-CoA reaching the TCA cycle increased and the mole fraction of 3HB units relatively decreased while the mole flux of 4HB-CoA was likely independent on the limitation of nitrogen source. It has been reported that the molar fraction of 4HB in P(3HB-co-4HB) biosynthesis by R. eutropha strain H16 was increased significantly under C/N ratio of 10 and the P(4HB) homopolymer was produced at 120 h [10]. It was suggested that in the presence of a nitrogen source, the acetyl-CoA concentration increased and the overflowing acetyl-CoA to TCA cycle seemed to cause an inhibitory effect on the ketolysis reaction catalyzing the lysis of 4-hydroxybutyratly-CoA to two molecules of acetyl-CoA, consequently, the 4HB fraction available for polymerization increased [9].…”

Re-Use of Vegetable Wastes as Cheap Substrates for Extremophile Biomass Production

“…Notably, the polymer produced on carrot medium showed spectral features different from those of PHB recovered in standard growth conditions. The chemical shift values (Table 3) relative to three equally intense signals, matched those already reported for the three methylene groups in the 4-hydroxybutyric acid unit [21]. The chemical nature of polyhydroxybutyrate is usually affected by the type of carbon source provided as already shown in literature in the case of microbial production of different isomers of PHBs [22].…”

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

“…We reported previously that P(3HB‐ co ‐4HB) copolymers with compositions of 66–82 mol% 4HB were produced by cultivating W. eutropha H16 for 48 h in medium containing 4HBA and carbon sources unrelated to β‐oxidation metabolism such as acetic acid and glucose in the presence of ammonium sulfate 28. However, the copolymer contents in dry cell weights and polyester yields were as low as 6.5 wt% and up to 0.34 g L −1 respectively.…”

“…In a previous study, we reported that wild‐type Ralstonia eutropha (now known as Wautersia eutropha ) could biosynthesize effectively P(4HB) homopolymer and P(3HB‐ co ‐4HB) copolymers with high 4HB molar fractions when it was cultivated in a medium containing 4HBA and propionic acid as mixed carbon substrates in the presence of ammonium sulfate 28. Further, we found that the cell mass increased at initial cultivation time when different α‐amino acids as both carbon and nitrogen sources were fed to wild‐type W. eutropha 29.…”