- Biosynthesis, Modification, and Biodegradation of Bacterial Medium-Chain-Length Polyhydroxyalkanoates
-
Do Young Kim , Hyung Woo Kim , Moon Gyu Chung , Young Ha Rhee
-
J. Microbiol. 2007;45(2):87-97.
-
DOI: https://doi.org/2528 [pii]
-
-
 Abstract
 PDF
-
Medium-chain-length polyhydroxyalkanoates (MCL-PHAs), which have constituents with a typical chain length of C6-C14, are polyesters that are synthesized and accumulated in a wide variety of Gram-negative bacteria, mainly pseudomonads. These biopolyesters are promising materials for various applications because they have useful mechanical properties and are biodegradable and biocompatible. The versatile metabolic capacity of some Pseudomonas spp. enables them to synthesize MCL-PHAs that contain various functional substituents; these MCL-PHAs are of great interest because these functional groups can improve the physical properties of the polymers, allowing the creation of tailor-made products. Moreover, some functional substituents can be modified by chemical reactions to obtain more useful groups that can extend the potential applications of MCL-PHAs as environmentally friendly polymers and functional biomaterials for use in biomedical fields. Although MCL-PHAs are water-insoluble, hydrophobic polymers, they can be degraded by microorganisms that produce extracellular MCL-PHA depolymerase. MCL-PHA-degraders are relatively uncommon in natural environments and, to date, only a limited number of MCL-PHA depolymerases have been investigated at the molecular level. All known MCL-PHA depolymerases share a highly significant similarity in amino acid sequences, as well as several enzymatic characteristics. This paper reviews recent advances in our knowledge of MCL-PHAs, with particular emphasis on the findings by our research group.
- 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
PDF
-
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.
- Purification and Characterization of Poly(3-hydroxybutyrate) Depolymerase from a Fungal Isolate, Emericellopsis minima W2
-
Do Young Kim , Ji Hye Yun , Hyung Woo Kim , Kyung Sook Bae , Young Ha Rhee
-
J. Microbiol. 2002;40(2):129-133.
-
-
-
Abstract
PDF
-
The fungus, Emericellopsis minima W2, capable of degrading poly(3-hydroxybutyrate) (PHB) was isolated from a waste water sample. Production of the PHB depolymerase from E. minima W2 (PhaZ_Emi ) was significantly repressed in the presence of glucose. PhaZ_Emi was purified by column chromatography on Octyl-Sepharose CL-4B and Sephadex G-100. The molecular mass of the PhaZ_Emi , which consisted of a single polypeptide chain, was estimated to be 48.0 kDa by SDS-PAGE and its pI value was 4.4. The maximum activity of the PhaZ_Emi was observed at pH 9.0 and 55 C. It was significantly inactivated by 1 mM dithiothreitol, 2 mM diisopropyl fluorophosphate, 0.1 mM Tween 80, and 0.1 mM Triton X-100, but insensitive to phenylmethylsulfonyl fluoride and N-ethylmaleimide. The PhaZ_Emi efficiently hydrolyzed PHB and its copolyester with 30 mol% 3-hydroxyvalerate, but did not act on poly(3-hydroxyoctanoate). It also hydrolyzed p-nitrophenylacetate and p-nitrophenylbutyrate but hardly affected the longer-chain forms. The main hydrolysis product of PHB was identified as a dimer of 3-hydroxybutyrate.
- 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
PDF
-
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.
|
MSK
