Journal of Microbiology

Research Support, Non-U.S. Gov't

Enzymatic and Non-enzymatic Degradation of Poly (3-Hydroxybutyrate-co-3-Hydroxyvalerate) Copolyesters Produced by Alcaligenes sp. MT-16: Gang Guk Choi , Hyung Woo Kim , Young Ha Rhee; J. Microbiol. 2004;42(4):346-352.; DOI: https://doi.org/2100 [pii]

Abstract: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3HB-co-3HV), copolyesters with a variety of 3HV contents (ranging from 17 to 60 mol%) were produced by Alcaligenes sp. MT-16 grown on a medium containing glucose and levulinic acid in various ratios, and the effects of hydrophilicity and crystallinity on the degradability of the copolyesters were evaluated. Measurements of thermo-mechanical properties and Fourier-transform infrared spectroscopy in the attenuated total reflectance revealed that the hydrophilicity and crystallinity of poly(3HB-co-3HV) copolyesters decreased as 3HV content in the copolyester increased. When the prepared copolyester film samples were non-enzymatically hydrolysed in 0.01 N NaOH solution, the weights of all samples were found to have undergone no changes over a period of 20 weeks. In contrast, the copolyester film samples were degraded by the action of extracellular polyhydroxybutyrate depolymerase from Emericellopsis minima W2. The overall rate of weight loss was higher in the films containing higher amounts of 3HV, suggesting that the enzymatic degradation of the copolyester is more dependent on the crystallinity of the copolyester than on its hydrophilicity. Our results suggest that the degradability characteristics of poly(3HB-co-3HV) copolyesters, as well as their thermo-mechanical properties, are greatly influenced by the 3HV content in the copolyesters.

Culture conditions affecting the molecular weight distribution of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesized by alcaligenaes sp. SH-69: Yoon, Joo Seok , Park, Sang Kyu , Kim, Young Baek , Maeng, Hack Young , Rhee, Young Ha; J. Microbiol. 1996;34(3):279-283.

Abstract: The weight average molecular weight of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesized by Alcaligenes sp. SH-69 was altered between 3.2 × 10^5 and 1.1 × 10^6 depending upon various culture conditions. It appeared that culture conditions favorable for the efficient production of copolyesters promoted the formation of higher molecular weight copolyesters. Polydispersity indices of isolated copolyesters were in the range of 1.5 to 2.5.

Effect of Levulinic Acid on the Production of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by Ralstonia eutropha KHB-8862: Sun Ho Chung , Gang Guk Choi , Hyung Woo Kim , Young Ha Rhee; J. Microbiol. 2001;39(1):79-82.

Abstract: The influence of levulinic acid (LA) on the production of copolyester consisting of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) by Ralstonia eutropha was investigated. Addition of LA into the culture medium greatly increased the molar fraction of 3HV in the copolyester, indicating that LA can be utilized as a precursor of 3HV. In shake flask culture, the 3HV content in the copolyester increased from 7 to 75 mol% by adding 0.5 to 4.0 g/L LA to the medium containing fructose syrup as a main carbon source. A maximal copolyester concentration of 3.6 g/L (69% of dry cell weight) was achieved with a 3HV content of 40 mol% in a jar fermentor culture containing 4.0 g/L of LA. When LA (total concentration, 4 g/L) was added repeatedly into a fermentor culture to maintain its concentration at a low level, the copolyester content and the 3HV yield from LA reached up to 85% of dry cell weight and 5.0 g/g, respectively, which were significantly higher than those when the same concentration of the LA was supplied all at once. The present results indicated that LA is more effective than propionate or valerate as a cosubstrate for the production of copolyesters with varying molar fractions of 3HV by R. eutropha.

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