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PubMed1990

Occurrence, metabolism, metabolic role, and industrial uses of bacterial polyhydroxyalkanoates.

Polyhydroxyalkanoates (PHAs), of which polyhydroxybutyrate (PHB) is the most abundant, are bacterial carbon and energy reserve materials of widespread occurrence. They are composed of 3-hydroxyacid monomer units and exist as a small number of cytoplasmic granules per cell. The properties of the C4 homopolymer PHB as a biodegradable thermoplastic first attracted industrial attention more than 20 years ago. Copolymers of C4 (3-hydroxybutyrate [3HB]) and C5 (3-hydroxyvalerate [3HV]) monomer units have modified physical properties; e.g., the plastic is less brittle than PHB, whereas PHAs containing C8 to C12 monomers behave as elastomers. This family of materials is the centre of considerable commercial interest, and 3HB-co-3HV copolymers have been marketed by ICI plc as Biopol. The known polymers exist as 2(1) helices with the fiber repeat decreasing from 0.596 nm for PHB to about 0.45 nm for C8 to C10 polymers. Novel copolymers with a backbone of 3HB and 4HB have been obtained. The native granules contain noncrystalline polymer, and water may possibly act as a plasticizer. Although the biosynthesis and regulation of PHB are generally well understood, the corresponding information for the synthesis of long-side-chain PHAs from alkanes, alcohols, and organic acids is still incomplete. The precise mechanisms of action of the polymerizing and depolymerizing enzymes also remain to be established. The structural genes for the three key enzymes of PHB synthesis from acetyl coenzyme A in Alcaligenes eutrophus have been cloned, sequenced, and expressed in Escherichia coli. Polymer molecular weights appear to be species specific. The factors influencing the commercial choice of organism, substrate, and isolation process are discussed. The physiological functions of PHB as a reserve material and in symbiotic nitrogen fixation and its presence in bacterial plasma membranes and putative role in transformability and calcium signaling are also considered.

Bacteria↗

PubMedDate not supplied

Reduction of surgery-induced peritoneal adhesions by continuous release of streptokinase from a drug delivery system.

Postoperative abdominal adhesions may lead to intestinal obstruction and infertility. The effect of continuous release of streptokinase to the peritoneal cavity on postoperative adhesions was examined under experimental conditions. Peritoneal adhesions were induced in rats and the animals were further treated by intraperitoneal administration of streptokinase solution, polyhydroxybutyrate-co-hydroxyvalerate (PHBV) membrane alone and streptokinase loaded PHBV membrane and compared to sham operated and untreated groups. Formation of adhesions was evaluated by quantitative macroscopic grading, histopathologically with light microscopy, on the following week. Streptokinase loaded PHBV prevented postoperative adhesion formation in 90% of the cases. PHBV membrane alone also reduced the severity of adhesions due to its anti-adhesive properties. Histopathological examination revealed limited foreign body reaction due to PHBV. Continuous streptokinase activity in the peritoneal cavity during early post-surgical period prevents postoperative adhesion.

Abdomen↗

PubMed1994

Enlargement of the right ventricular outflow tract and the pulmonary artery with a new biodegradable patch in transannular position.

Absorbable, nonwoven patches made from polyhydroxybutyrate (PHB) were implanted as transannular patches into the right ventricular outflow tract and pulmonary artery in 13 weanling sheep, the test group. Six sheep, in which a transannular Dacron patch was implanted, served as control group. The test and the control patches were harvested 3-24 months later. The results were documented macroscopically, by histological examination, and by scanning electron microscopy. The 6-keto-PGF1 alpha activity was measured in the regenerated tissue and compared with that in the native pulmonary artery. No aneurysms were noted. Regeneration of a neointima and a neomedia, comparable to native arterial tissue, was observed in the test group. In the control group, a neointimal layer was present but no neomedia comparable to native arterial tissue. Scanning electron microscopy disclosed differences in the endothelial structure between the test and control groups. 6-keto-PGF1 alpha activity was present in both the test and control groups. It is concluded that absorbable, nonwoven patches of PHB can be used as a scaffold for tissue regeneration in low-pressure systems. The regenerated vessel had structural and biochemical qualities in common with the native pulmonary artery.

6-Ketoprostaglandin F1 alpha↗

PubMed2005

Degradation of P(3HB) and P(3HB-co-3HV) in biological media.

The biodegradability of oriented fibers made of polyhydroxybutyrate (P(3HB)) and its co-polymer with beta-hydroxyvalerate (P(3HB-co-3HV)) was investigated in buffer solutions and in biological media in vitro and in vivo. The fibers of both polymer types demonstrated resistance to hydrolytic degradation in buffer solutions at 38 degrees C and pH from 4.5 to 7.0 (for up to 180 days). It has been found that the biodegradation of the fibers in vitro in blood and serum and in vivo is accompanied by weight losses and minor changes in the microstructure with no significant losses in the tensile strength over a long time (up to 180 days). The biodegradation rate of the less crystalline co-polymer P(3HB-co-3HV) fibers was 1.4-2.0-times higher than that of the homopolymer P(3HB). It has also been shown that the degradation of the fibers in vivo is influenced both by tissue fluid enzymes and cells (macrophages and foreign-body giant cells). The fibers were eroded on the surface only with no gross defects and no dramatic effects on their mechanical performance.

Animals↗

PubMed2006

Morphologies of fibroblast cells cultured on surfaces of PHB films implanted by hydroxyl ions.

Polyhydroxybutyrate (PHB) films were implanted with 40 keV hydroxyl ions with fluences ranging from 1 x 10(12) to 1 x 10(15) ions/cm2, respectively. The as-implanted PHB films were characterized by scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA) and water contact angle measurements. The surface structures and properties of the as-implanted PHB films were closely related with hydroxyl ion fluence. They were further investigated by inoculating 3T6 fibroblasts cells on their surfaces. Morphologies of the 3T6 fibroblast cells cultured on surfaces of the as-implanted PHB films were observed by SEM. Characterization of the cultural 3T6 cells was analyzed qualitatively. The preliminary experimental results reveal that the bioactivity of the PHB films modified by hydroxyl ion implantation was improved at different levels, and the fluence of 1 x 10(13) ions/cm2 is optimal for PHB film.

Animals↗

PubMed2005

Fabrication, characterization, and in vitro degradation of composite scaffolds based on PHBV and bioactive glass.

Composite scaffolds of polyhydroxybutyrate-polyhydroxyvalerate (PHBV) with sol-gel-derived bioactive glass (BG, 58S) are fabricated by compression molding, thermal processing, and salt particulate leaching method. Structure and mechanical properties of the scaffolds are determined. The bioactivity of the composites is evaluated by soaking the scaffolds in a simulated body fluid (SBF), and the formation of the apatite layer on the scaffolds is determined by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). The results show that the PHBV/BG composites are bioactive as they induce the formation of apatite on the composite scaffolds after soaking in SBF for 3 days. In addition, the measurements of the water contact angles suggest that incorporation of BG into PHBV can improve the hydrophilicity of the composites and the enhancement is dependent on the BG content. Furthermore, the degradation assessment of the scaffolds is performed in phosphate-buffered saline (PBS) solution at 37 C. Weight loss and water absorption of the scaffolds, pH of the incubation media, and molecular weight measurements of the PHBV in the scaffolds are used to monitor the degradation of the scaffolds during a nine-week incubation in PBS. It has been found that the incorporation of bioactive glass into the PHBV delayed the degradation of PHBV in the composite scaffolds for the period investigated. The present results show not only a useful method to prepare composite scaffolds with improved properties but also a way of adjusting the in vitro degradation behavior of composite scaffolds by tailoring the content of bioactive glass.

Biocompatible Materials↗

PubMed2005

A composite of hydroxyapatite with electrospun biodegradable nanofibers as a tissue engineering material.

Biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as a nanofibrous film by electrospinning and composited with hydroxyapatite (HAp) by soaking in simulated body fluid. Compared with a PHBV cast (flat) film, the electrospun PHBV nanofibrous film was hydrophobic. However, after HAp deposition, both of the surfaces were extremely hydrophilic. The degradation rate of HAp/PHBV nanofibrous films in the presence of polyhydroxybutyrate depolymerase was very fast. Nanofiber formation increased the specific surface area and HAp enhanced the invasion of enzyme into the film by increasing surface hydrophilicity. The surface of the nanofibrous film showed enhanced cell adhesion over that of the flat film, although cell adhesion was not significantly affected by the combination with HAp.

Absorbable Implants↗

PubMed2001

Introduction of bacterial metabolism into higher plants by polycistronic transgene expression.

Multiple-gene transformation is required to improve or change plant metabolisms effectively; but this many-step procedure is time-consuming and costing. We succeeded in the metabolic engineering of tobacco plants by introducing multiple genes as a bacteria-type operon into a plastid genome. The tobacco plastid was transformed with a polycistron consisting of three bacterial genes for the biosynthesis of a biodegradable polyester, polyhydroxybutyrate (PHB). Accumulation of PHB in the leaves of the transgenic tobacco indicated that the introduced genes were polycistronically expressed. This "phyto-fermentation" system can be used in plant production of various chemical commodities and pharmaceuticals.

Acetyl-CoA C-Acyltransferase↗

PubMed2001

Production of poly(3-hydroxybutyrateco-3-hydroxyvalerate) from cottonseed oil and valeric acid in batch culture of Raistonia sp. strain JC-64.

A Ralstonia sp. strain JC-64 that is capable of accumulating poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[3HB-co-3HV]) from cottonseed oil and valeric acid was isolated. By using a high limiting-nitrogen (HLN) mineral medium as the medium for the second stage of the fermentation process and by adding the two carbon sources at different times, a range of copolymers with 12-62 mol% of 3HV were produced from a series of HLN mineral mediums containing different compositions of cottonseed oil and valeric acid by Ralstonia sp. JC-64. The melting temperature (Tm) of polyhydroxybutyrate from cottonseed oil was 174 degrees C and that of P(3HB-co-3HV) with the highest 3HV-mol fraction (62%) was 81 degrees C.

Carbon↗

PubMedDate not supplied

Development of a natural degradable polymer for orthopaedic use.

Currently, there are a large variety of degradable polymers available for use in surgery, which are generally based on blends and copolymers of poly(L-lactide) (PLLA) and poly(L-glycolide) (PGA). The major demand for these materials is for suturing of wounds, but the materials are also being developed for use in orthopaedic surgery for fracture reduction. The development of these materials is on two fronts, the first involving conventional fracture fixation design of plates. The second is to produce simple devices such as rods and to use the degradable materials for treatment of specific fracture types such as fractures of the olecranon. These materials have the advantage of possessing initially enhanced mechanical properties, although their relatively quick degradation profile diminishes these properties. As an alternative we are developing polyhydroxybutyrate (PHB) and its copolymers with polyhydroxyvalerate (PHV). This range of polymers mab be easily thermally processed, are very cheap and easily available. The polymer also has the significant advantage of being piezoelectric. This is discussed.

Animals↗

PubMedDate not supplied

[Physicochemical properties of two-component polyhydroxyalkanoates based on 3-hydroxybutyrate and 3-hydroxyvalerate].

A series of two-component polyhydroxyalkanoates consisting of hydroxybutyrate and hydroxyvalerate monomer at different ratios were synthesized using the bacterium Ralstonia eutropha B5786. The properties of polyhydroxyalkanoates were compared with those of the homopolymer of hydroxybutyric acid by X-ray structure analysis, IR spectroscopy, differential scanning calorimetry, and viscosimetry. With an increase in the molar fraction of hydroxyvalerate, an equalization of the ratio of the crystalline and amorphous phases in the copolymer was observed. The degree of crystallinity of the polymer decreased from 70-80 to 45-50%; in the range of an increase in the hydroxyvalerate molar fraction from several to 25-30 mol%, the dependence was linear. The temperature characteristics, the melting temperature (T(m)), and the degradation temperature (T(d)) were lower in polyhydroxyalkanoates than in polyhydroxybutyrate, for which T(m) and T(d) were 168-170 and 260-265 degrees C, respectively. In the copolymer, as the molar fraction of hydroxyvalerate grew, both parameters decreased. In the range of variation of monomer ratio studied, they decreased to 150-160 and 200-220 degrees C, respectively. No distinct correlation between the composition of the polymer and its molecular mass was found.

Butyrates↗

PubMed2004

Enzymatic and non-enzymatic degradation of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) copolyesters produced by Alcaligenes sp. MT-16.

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.

Acyltransferases↗

PubMed2004

Polyhydroxyalkanoates production by activated sludge in a SBR using acetate and propionate as carbon sources.

In this work, sludge was submitted to aerobic dynamic substrate feeding. Two sequencing batch reactors were operated, with acetate or propionate as carbon substrates. When acetate was used the system only produced a homopolymer of polyhydroxybutyrate (PHB). In order to maximize the PHB production, tests with different concentrations of acetate and ammonia were preformed. The best results (67.2% of PHB by cell dry weight) were obtained for 0.7 Nmmol/l of ammonia and 180 Cmmol/l of acetate. The PHB cell content was further improved by pulse addition of substrate, three times 60 Cmmol/l of acetate, reaching a value of 78.5%. Propionate can be used as a precursor for hydroxyvalerate. In conjunction with other substrates, it allows for the formation of copolymers, which present better processing properties on commercial applications. Tests with different concentrations of propionate and ammonia were performed. Under the operating conditions used, the maximum PHA accumulated inside cells was 34.8%, with 30 Cmmol/l of propionate and no ammonia.

Acetates↗

PubMed1999

Chiral compounds from bacterial polyesters: sugars to plastics to fine chemicals.

A novel and efficient method for the production of enantiomerically pure (R)-(-)-hydroxycarboxylic acids by in vivo depolymerization of microbial polyester polyhydroxyalkanoates (PHAs) was developed. Using this method, several model compounds, (R)-(-)-3-hydroxyalkanoic acids, consisting of 4 to 12 carbon atoms, and (R)-(-)-3-hydroxy-5-phenylvaleric acid, could be prepared. In particular, (R)-(-)-3-hydroxybutyric acid could be efficiently prepared by this method. By providing the environmental condition in which cells possess high activity of intracellular PHA depolymerase and low activity of (R)-(-)-3-hydroxybutyric acid dehydrogenase, (R)-(-)-3-hydroxybutyric acid could be produced with a yield of 96% in only 30 min by in vivo depolymerization of polyhydroxybutyrate (PHB) accumulated in Alcaligenes latus.

Bacteria↗

PubMed2001

Metabolic flux modeling of detoxification of acetic acid by Ralstonia eutropha at slightly alkaline pH levels.

Ralstonia eutropha grows on and produces polyhydroxyalkanoates (PHAs) from fermentation acids. Acetic acid, one major organic acid from acidogenesis of organic wastes, has an inhibitory effect on the bacterium at slightly alkaline pH (6 g HAc/L at pH 8). The tolerance of R. eutropha to acetate, however, was increased significantly up to 15 g/L at the slightly alkaline pH level with high cell mass concentration. A metabolic cell model with five fluxes is proposed to depict the detoxification mechanism including mass transfer and acetyl-CoA formation of acetic acid and the formation of three final metabolic products, polyhydroxybutyrate (PHB), active biomass, and CO(2). The fluxes were measured under different conditions such as cell mass concentration, acetic acid concentration, and medium composition. The experimental results indicate that the acetate detoxification by high cell mass concentration is attributed to the increased fluxes at high extracellular acetate concentrations. The fluxes could be doubled to reduce and hence detoxify the accumulated intracellular acetate anions.

Acetates↗

PubMed2004

Empirical modeling of batch fermentation kinetics for poly(glutamic acid) production and other microbial biopolymers.

An empirical kinetic model is proposed for the batch production of poly(glutamic acid) from Bacillus subtilis IFO 3335. In addition, the proposed model was used to fit the kinetic data of poly(glutamic acid) production from other bacterial strains using different media, as well as kinetic data from different strains for the production of the exocellular biopolymers dextran, hyaluronic acid, xanthan, alginate, and the endocellular biopolymer polyhydroxybutyrate. The empirical model treats the biopolymer as a component of the biomass and fits the experimental biomass data using a sigmoidal relationship that includes the maximum specific growth rate, mu(max), and the substrate saturation parameter, K(S). An empirical parameter, the relative coefficient (r), quantifies, in relative terms, the degree of nongrowth-associated biopolymer formation.

Bacillus subtilis↗

PubMed2005

Strong fibers and films of microbial polyesters.

Poly[(R)-3-hydroxybutyrate] (P(3HB)) and its copolymers are accumulated by a wide variety of microorganisms as intracellular carbon and energy material, and are extensively studied as biodegradable and biocompatible thermoplastics. However, these microbial polyesters have not been recognized as practical because of their stiffness and brittleness. Recently, by new drawing techniques, we succeeded in obtaining strong fibers and films from microbial polyesters, produced by both wild-type and recombinant bacteria. The improvement in mechanical properties of the fibers and films is due not only to the orientation of molecular chains, but also to the generation of a zigzag conformation and network structure, formed by fibrillar and lamellar crystals. The structure of strong fibers with a tensile strength over 1.0 GPa was analyzed by micro-beam X-ray diffraction with synchrotron radiation. The strong fibers and films were completely degraded in natural, river freshwater or by extracellular polyhydroxybutyrate depolymerases. In this feature article, the processing, mechanical properties, highly ordered structure and biodegradability of strong fibers and films produced from microbial polyesters are presented.

3-Hydroxybutyric Acid↗

PubMed2001

Class I and III polyhydroxyalkanoate synthases from Ralstonia eutropha and Allochromatium vinosum: characterization and substrate specificity studies.

Class I and III polyhydroxyalkanoate (PHA) synthases catalyze the conversion of beta-hydroxybutyryl coenzyme A (HBCoA) to polyhydroxybutyrate. The Class I PHA synthase from Ralstonia eutropha has been purified by numerous labs with reported specific activities that vary between 1 and 160 U/mg. An N-terminal (His)6-PHA synthase was constructed and purified with specific activity of 40 U/mg. The variable activity is shown to be related to the protein's propensity to aggregate and not to incomplete post-translational modification by coenzyme A and a phosphopantetheinyl transferase. The substrate specificities of this enzyme and the Class III PHA synthase from Allochromatium vinosum have been determined with nine analogs of varied chain length and branching, OH group position within the chain, and thioesters. The results suggest that in vitro, both PHA synthases are very specific and provide further support for their active site structural similarities. In vitro results differ from studies in vivo.

Acyltransferases↗