Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polyhydroxybutyrates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed2002

Effect of allogeneic Schwann cell transplantation on peripheral nerve regeneration.

Transplantation of allogeneic Schwann cells (SC) would make it feasible to reconstruct immediately peripheral nerve defects, compared to using autologous SC; however, this treatment modality has not been adequately evaluated. The aim of this study was to characterize and compare the effects of allogeneic versus syngeneic SC transplantation following peripheral nerve injury. Polyhydroxybutyrate conduits were used to bridge a 10-mm gap in the rat sciatic nerve. The conduits were filled with alginate hydrogel with or without cultured allogeneic or syngeneic genetically labeled SC, without the use of immunosuppressive therapy, and examined after 2, 3, and 6 weeks with 5-bromo-4-chloro-3-indoyl-beta-D-galactosidase chemical staining and immunohistochemistry to quantify SC migration into the conduit, axonal regeneration, the state of SC differentiation, and the expression of major histocompatibility complexes (MHC) I and II, as well as to quantify macrophage and B- and T-lymphocyte infiltration. Allogeneic SC were rejected by 6 weeks, whereas syngeneic SC could still be identified. Allogeneic and syngeneic SC equally enhanced the axonal regeneration distance but the quantity of axons was greater using syngeneic SC. The ingrowth of SC into the conduits containing allogeneic SC was similar to that observed in the presence of syngeneic SC, indicating the absence of deleterious immune response. SC continued to express phenotypic markers of nonmyelination and these were highest in conduits with allogeneic SC. Expression of MHC I and II was higher in the conduits with allogeneic SC at 3 weeks and without significant difference in the number of macrophages and lymphocytes, except at 6 weeks, when there was a larger number of lymphocytes using syngeneic SC. In conclusion, allogeneic SC enhanced axonal regeneration distance and did not induce a deleterious immune response. In a clinical setting the immediate availability of allogeneic SC for transplantation may compensate for the better outcome achieved by the use of autologous SC that require a longer preparation time in culture.

Alginates↗
PubMed2001

Production of polyesters in transgenic plants.

Polyhydroxyalkanoates (PHAs) are bacterial polyesters having the properties of biodegradable thermoplastics and elastomers. Synthesis of PHAs has been demonstrated in transgenic plants. Both polyhydroxybutyrate and the co-polymer poly(hydroxybutyrate-co-hydroxyvalerate) have been synthesized in the plastids of Arabidopsis thaliana and Brassica napus. Furthermore, a range of medium-chain-length PHAs has also been produced in plant peroxisomes. Development of agricultural crops to produce PHA on a large scale and at low cost will be a challenging task requiring a coordinated and stable expression of several genes. Novel extraction methods designed to maximize the use of harvested plants for PHA, oil, carbohydrate, and feed production will be needed. In addition to their use as plastics, PHAs can also be used to modify fiber properties in plants such as cotton. Furthermore, PHA can be exploited as a novel tool to study the carbon flux through various metabolic pathways, such as the fatty acid beta-oxidation cycle.

Arabidopsis↗
PubMed1978

Growth of a photosynthetic bacterium anaerobically in darkness, supported by "oxidant-dependent" sugar fermentation.

Rhodopseudomonas capsulata can obtain energy for growth from light (anaerobically) and can also grow heterotrophically in darkness using alternative energy conversion modes, namely, aerobic respiration or an unusual type of anaerobic catabolism of sugars. Dark anaerobic growth with fructose as sole carbon and energy source is dependent on the presence of an "accessory" oxidant such as trimethylamine-N-oxide, is accompanied by production of lactate and other classical fermentation products, and yields cells with a high content of photosynthetic pigments and polyhydroxybutyrate.

Anaerobiosis↗
PubMed2004

Polyhydroxyalkanoate (PHA) granule formation in Ralstonia eutropha cells: a computer simulation.

Computer simulation of polyhydroxyalkanoate (PHA) granule formation in vivo could help to design strategies to optimize the fermentation process and achieve higher yields of PHA. It could also suggest biotechnological approaches to control the granule size and molecular weight of the polymer. A computer program simulating the formation of PHA granules inside a Ralstonia eutropha cell was developed, based on published experimental data. The results are applicable to R. eutropha cells or other microorganisms and transgenic plants, where polyhydroxybutyrate production is made possible by heterologous expression systems. The simulation starts at the outset of the PHA accumulation phase when the cells are small and contain no PHA granules. In the presence of abundant glucose, the cell responds to phosphorus limitation by producing 3-hydroxybutyryl-CoA which undergoes polymerization on the few PHA synthase molecules present in the cytoplasm. The amphiphilic PHA synthase-PHA complex attracts additional PHA synthase molecules and granules begin to grow from these initiation sites. Phosphorus limitation and the appearance of PHA in the cytoplasm also stimulate production of phasin molecules that attach themselves to the growing granules. As the granules grow bigger, they begin to touch each other and move to optimize their packing. The phasin coat prevents the granules from coalescing. The size of the cell increases and its prolate ellipsoid shape becomes closer to spherical. The accumulation process stops either when the supply of glucose is exhausted or when the granules become tightly packed within the cell, so that access to their surface is limited. All important variables, such as cell dimensions, granule size, counts of granule-associated molecules, PHA yield, degree of polymerization of the PHA molecules, etc., are recorded in real time during the simulation. Examples of virtual experiments with the cell and their results are shown.

Acyltransferases↗
PubMed2005

Comparative study of promoters for the production of polyhydroxyalkanoates in recombinant strains of Wautersia eutropha.

Recombinant strains of Wautersia eutropha expressing an artificial polyhydroxyalkanoate (PHA) biosynthesis operon under the control of different native promoters linked to polyhydroxybutyrate (PHB) (P(phb)), acetoin (P(acoE), P(acoD), and P(acoX)) or pyruvate (P(pdhE)) metabolism were constructed and tested. The promoters were representative either of the enterobacterial sigma70 (P(phb), P(acoE), and P(pdhE))- or sigma54 (P(acoD) and P(acoX))-dependent promoters. To obtain polymers consisting of C4-C12 monomer units, an artificial operon consisting of the PHA synthase gene from Pseudomonas sp. 61-3 (phaC1 (Ps)) tandemly linked to the W. eutropha genes encoding beta-ketothiolase (phbA (We)) and nicotinamide adenine dinucleotide phosphate dependent acetoacetyl-coenzyme A (CoA) reductase (phbB (We)) was constructed. All recombinant strains produced PHA, indicating that the PHA biosynthesis genes were expressed under the control of the different promoters. Cell growth and PHA synthesis on MS medium complemented with gluconate or octanoate, and different concentrations of acetoin (0, 0.15, and 0.3%) clearly differed among the recombinant strains. While the P(acoD) and P(acoX) promoters mediated only low PHA yields (<1%) in the presence of the inducer acetoin, the remaining promoters-independent of the addition of acetoin-resulted in the production of PHA polymers with high 3HB fractions (90-100 mol%) and with high 3HO contents (70-86 mol%) from gluconate and octanoate, respectively. Interestingly, on octanoate-MS medium with 0.15% acetoin, the P(acoE) promoter mediated the synthesis of PHA with a relatively high 3HB fraction (48 mol%). While PHAs with high 3HB contents were obtained, the overall PHA product yields were low (<10%); thus, their potential application for further commercial exploitation appears limited.

Acetoin↗
PubMed2006

A lower specificity PhaC2 synthase from Pseudomonas stutzeri catalyses the production of copolyesters consisting of short-chain-length and medium-chain-length 3-hydroxyalkanoates.

A polyhydroxyalkanoate (PHA) synthase gene phaC2 (Ps) from Pseudomonas stutzeri strain 1317 was introduced into a PHA synthase gene phbC (Re) negative mutant, Ralstonia eutropha PHB(-)4. It conferred on the host strain the ability to synthesize PHA, the monomer compositions of which varied widely when grown on different carbon sources. During cultivation on gluconate, the presence of phaC2 (Ps) in R. eutropha PHB(-)4 led to the accumulation of polyhydroxybutyrate (PHB) homopolymer in an amount of 40.9 wt% in dry cells. With fatty acids, the recombinant successfully produced PHA copolyesters containing both short-chain-length and medium-chain-length 3-hydroxyalkanoate (3HA) of 4-12 carbon atoms in length. When cultivated on a mixture of gluconate and fatty acid, the monomer composition of accumulated PHA was greatly affected and the monomer content was easily regulated by the addition of fatty acids in the cultivation medium. After the (R)-3-hydroxydecanol-ACP:CoA transacylase gene phaG (Pp) from Pseudomonas putida was introduced into phaC2(Ps)-containing R. eutropha PHB(-)4, poly(3HB-co-3HA) copolyester with a very high 3-hydroxybutyrate (3HB) fraction (97.3 mol%) was produced from gluconate and the monomer compositions of PHA synthesized from fatty acids were also altered. This study clearly demonstrated that PhaC2(Ps) cloned from P. stutzeri 1317 has extraordinarily low substrate specificity in vivo, though it has only 54% identity in comparison to a previously described low-substrate-specificity PHA synthase PhaC1(Ps) from Pseudomonas sp. 61-3. This study also indicated that the monomer composition and content of the synthesized PHA can be effectively modulated by controlling the addition of carbon sources or by modifying metabolic pathways in the hosts.

Acyltransferases↗
PubMed1990

Polymers for biodegradable medical devices. V. Hydroxybutyrate-hydroxyvalerate copolymers: effects of polymer processing on hydrolytic degradation.

The effects of melt processing on those properties of polyhydroxybutyrate-hydroxyvalerate copolymers that control hydrolytic stability were studied. Initial experiments using a non-thermal preparation technique enabled the relationship between initial molecular weight and rate of hydrolytic degradation to be established. This rate was conveniently expressed in terms of the time for 10% by weight of the sample to be eroded. By varying melt processing conditions, the range of effects of processing on sample molecular weight and molecular weight distribution were investigated. These effects were found to be quite dramatic, with a reduction to 50% of the initial molecular weight being readily achieved. Temperature, shear rate and dwell time interrelated to control the extent of thermal degradation achieved during processing. The principal effect of copolymer composition resulted from the fact that an increase in hydroxyvalerate content led to a reduction in melting point and enabled milder processing conditions to be used. Enhanced crystallinity, resulting from more favourable processing conditions reduced hydrolytic degradation rates. As a result, melt processing produced a complex interrelation of effects, all of which influenced the hydrolytic stability of the fabricated specimen. In general, molecular weight effects predominated.

Biodegradation, Environmental↗
PubMed1992

Identification, cloning and sequence analysis of the poly(3-hydroxyalkanoic acid) synthase gene of the gram-positive bacterium Rhodococcus ruber.

The first polyhydroxyalkanoic acid (PHA) synthase gene (phbCRr) of a Gram-positive bacterium was cloned from a genomic library of Rhodococcus ruber in the broad-host-range plasmid vector pRK404. The hybrid plasmid harboring phbCRr allowed the expression of polyhydroxybutyric acid (PHB) synthase activity and restored the ability of PHB synthesis in a PHB-negative mutant of Alcaligenes eutrophus. Nucleotide sequence analysis of phbCRr revealed an open reading frame of 1686 bp starting with the rare codon TTG and encoding a protein of relative molecular mass 61,371. The deduced amino acid sequence of phbCRr exhibited homologies to the primary structures of the PHA synthases of A. eutrophus and Pseudomonas oleovorans. Preparation of PHA granules by discontinuous density gradient centrifugation of crude cellular extracts revealed four major bands in an SDS polyacrylamide gel. A Mr 61,000 protein was identified as the PHA synthase of R. ruber by N-terminal amino acid sequence determination.

Acyltransferases↗
PubMed1995

The development of Azospirillum as a commercial inoculant for improving crop yields.

Bacteria of the genus Azospirillum are nitrogen-fixing organisms that live in close association with plants in the rhizosphere. The Azospirillum-plant association leads to the enhanced development and yield of different host plants under appropriate growth conditions. This increase in yield is attributed mainly to an improvement in root development, an increase in the rate of water and mineral uptake by roots, and to a lesser extent, biological N(2) fixation. Worldwide data accumulated in the field over the past 20 years indicates that Azospirillum is capable of promoting the yield of agriculturally important crops in different soils and climatic regions. A.brasilense shows both chemotaxis and chemokinesis in response to temporal gradients of different chemoeffectors, thereby increasing the chance of root-bacterial interactions. Phytohormones synthesized by Azospirillum influence the host root respiration rate, metabolism and root proliferation and hence better the mineral and water uptake in inoculated plants. Positive effects of combined inoculation with Rhizobium have been reported for different legumes and were related to the favorable influence of Azospirillum on the nodule number, plant development, dry weight, and N(2) fixation. Additionally, A. brasilense produces the reserve material polyhydroxybutyrate comprising up to 70% of the cell dry weight This substance has received much attention recently as it can be extracted and formed into a biodegradable thermoplastic.

Journal Article↗
PubMed2004

Fabrication and characterization of bioactive wollastonite/PHBV composite scaffolds.

Composite scaffolds of polyhydroxybutyrate-polyhydroxyvalerate (PHBV) with bioactive wollastonite were fabricated by a compression moulding, thermal processing, and salt particulate leaching method. Structure and mechanical properties of the scaffolds were determined. The bioactivity of the composites was evaluated by soaking in a simulated body fluid (SBF), and the formation of the hydroxyapatite (HAp) layer was determined by Scanning Electron Microscope (SEM) and Energy-Dispersive Spectrometer (EDS). The results showed that the wollastonite/PHBV composites were bioactive as it induced the formation of HAp on the surface of the composite scaffolds after soaking in SBF for 14 days. In addition, the measurements of the water contact angles suggested that incorporation of wollastonite into PHBV could improve the hydrophilicity of the composites and the enhancement was dependent on the wollastonite content. Furthermore, the pH and ion concentration changes of SBF solutions with composite scaffolds showed that the composites released Ca and Si ions, which could neutralize the acidic by-products of the PHBV and stabilize the pH of the SBF solutions between 7.2 and 7.8 within a 3-week soaking period. All of these results suggest that the incorporation of wollastonite was a useful approach to obtain composite scaffolds with improved properties.

Biocompatible Materials↗
PubMed2006

The effect of D,L-beta-hydroxybutyric acid on cell death and proliferation in L929 cells.

As a prerequisite for tissue engineering applications, researchers must understand the effect on local cell types of the degradation products of biodegradable polymers. Polyhydroxybutyrate (PHB) has received special interest as an implant material, because it degrades to release a normal component of blood and tissue, D,L-beta-hydroxybutyrate (HB). We report that HB (0.02 g/l) promoted cell proliferation in cultured L929 cells plated at high cell density (1 x 10(5) cells/well) but not lower cell densities. While HB did not affect cell cycle progression, it significantly inhibited cell death. HB treatment prevented necrosis, reducing cell membrane permeability 4h following serum withdrawal from the medium, and for all subsequent time points. In summary, HB promotes proliferation of L929 cells in high-density cultures by preventing apoptotic and necrotic cell death. This property makes biodegradable polymers containing HB, such as PHBHHx, attractive candidates for tissue engineering applications, especially those requiring the regeneration of large numbers of cells.

3-Hydroxybutyric Acid↗
PubMed2003

Characterization of aldehyde ferredoxin oxidoreductase gene defective mutant in Magnetospirillum magneticum AMB-1.

A non-magnetic mutant of Magnetospirillum magneticum AMB-1, designated as NMA21, was generated by mini-Tn5 transposon mutagenesis to identify genes involved in bacterial magnetic particle (BMP) synthesis. Alignment of the DNA sequences flanking the transposon allowed the isolation of an open reading frame (ORF2) within an operon consisting of five genes. The amino acid sequence of ORF2 showed homology with tungsten-containing aldehyde ferredoxin oxidoreductase (AOR) from Pyrococcus furiosus (48% identity and 64% similarity), which functions for aldehyde oxidation. AOR was found to be expressed under microaerobic conditions and localized in the cytoplasm of AMB-1. Iron uptake and growth of NMA21 were lower than wild type. Transmission electron microscopy (TEM) of NMA21 revealed that no BMPs were completely synthesized, but polyhydroxybutyrate (PHB)-like granules were persistently produced. These results indicate that AOR may contribute to ferric iron reduction during BMP synthesis in M. magneticum AMB-1 under microaerobic respiration.

Aldehyde Oxidoreductases↗
PubMed2001

New developments in our understanding of the beta-hydroxyacid dehydrogenases.

The beta-hydroxyacid dehydrogenases are a structurally conserved family of enzymes that catalyze the NAD(+) or NADP(+)-dependent oxidation of specific beta-hydroxyacid substrates like beta-hydroxyisobutyrate. These enzymes share distinct domains of amino acid sequence homology, most of which now have assigned putative functions. 6-phosphogluconate dehydrogenase and beta-hydroxyisobutyrate dehydrogenase, the most well-characterized members, both appear to be readily inactivated by chemical modifiers of lysine residues, such as 2,4,6-trinitrobenzene sulfonate (TNBS). Peptide mapping by ESI-LCMS showed that inactivation of beta-hydroxyisobutyrate dehydrogenase with TNBS occurs with the labeling of a single lysine residue, K248. This lysine residue is completely conserved in all family members and may have structural importance relating to cofactor binding. The structural framework of the beta-hydroxyacid dehydrogenase family is shared by many bacterial homologues. One such homologue from E. coli has been cloned and expressed as recombinant protein. This protein was found to have enzymatic activity characteristic of tartronate semialdehyde reductase, an enzyme required for bacterial biosynthesis of D-glycerate. A homologue from H. influenzae was also cloned and expressed as recombinant protein. This protein was active in the oxidation of D-glycerate, but showed approximately ten-fold higher activity with four carbon substrates like beta-D-hydroxybutyrate and D-threonine. This enzyme might function in H. influenzae, and other species, in the utilization of polyhydroxybutyrates, an energy storage form specific to bacteria. Cloning and characterization of these bacterial beta-hydroxyacid dehydrogenases extends our knowledge of this enzyme family.

Amino Acid Sequence↗
PubMed2003

Effect of periodic feeding in sequencing batch reactor on substrate uptake and storage rates by a pure culture of Amaricoccus kaplicensis.

A pure culture of Amaricoccus kaplicensis was aerobically cultured at a long culture residence time (Theta(C)>12d), under periodic acetate feeding in a sequencing batch reactor (SBR). The cycle length and, correspondingly, the volumetric organic load rate (vOLR) were varied in the range 4-24h and 0.76-0.12gCODl(-1)d(-1), respectively. The transient response of the microorganism to the acetate spike was investigated throughout batch tests, as a function of SBR cycle length and vOLR. In all tested conditions, a rapid transient response was observed, mainly due to acetate storage in the form of polyhydroxybutyrate, since growth (production of active biomass) played a minor role. Apart from this general trend, the maximum rates under transient conditions increased as the cycle length increased from 4 to 24h. In the SBR, the longest cycle also caused a decrease in floc size and settleability as well as an increase in the observed yield. The observed effect of SBR operating conditions on the physiological state of cells and their related transient response may have great significance on the performance of full scale activated sludge processes.

Biomass↗
PubMed2004

The degradability of biodegradable plastics in aerobic and anaerobic waste landfill model reactors.

Degradabilities of four kinds of commercial biodegradable plastics (BPs), polyhydroxybutyrate and hydroxyvalerate (PHBV) plastic, polycaprolactone plastic (PCL), blend of starch and polyvinyl alcohol (SPVA) plastic and cellulose acetate (CA) plastic were investigated in waste landfill model reactors that were operated as anaerobically and aerobically. The application of forced aeration to the landfill reactor for supplying aerobic condition could potentially stimulate polymer-degrading microorganisms. However, the individual degradation behavior of BPs under the aerobic condition was completely different. PCL, a chemically synthesized BP, showed film breakage under the both conditions, which may have contributed to a reduction in the waste volume regardless of aerobic or anaerobic conditions. Effective degradation of PHBV plastic was observed in the aerobic condition, though insufficient degradation was observed in the anaerobic condition. But the aeration did not contribute much to accelerate the volume reduction of SPVA plastic and CA plastic. It could be said that the recalcitrant portions of the plastics such as polyvinyl alcohol in SPVA plastic and the highly substituted CA in CA plastic prevented the BP from degradation. These results indicated existence of the great variations in the degradability of BPs in aerobic and anaerobic waste landfills, and suggest that suitable technologies for managing the waste landfill must be combined with utilization of BPs in order to enhance the reduction of waste volume in landfill sites.

Anaerobiosis↗
PubMed2000

Carbon and nitrogen metabolism in Rhizobium.

One of the paradigms of symbiotic nitrogen fixation has been that bacteroids reduce N2 to ammonium and secrete it without assimilation into amino acids. This has recently been challenged by work with soybeans showing that only alanine is excreted in 15N2 labelling experiments. Work with peas shows that the bacteroid nitrogen secretion products during in vitro experiments depend on the experimental conditions. There is a mixed secretion of both ammonium and alanine depending critically on the concentration of bacteroids and ammonium concentration. The pathway of alanine synthesis has been shown to be via alanine dehydrogenase, and mutation of this enzyme indicates that in planta there is likely to be mixed secretion of ammonium and alanine. Alanine synthesis directly links carbon catabolism and nitrogen assimilation in the bacteroid. There is now overwhelming evidence that the principal carbon sources of bacteroids are the C4-dicarboxylic acids. This is based on labelling and bacteroid respiration data, and mutation of both the dicarboxylic acid transport system (dct) and malic enzyme. L-malate is at a key bifurcation point in bacteroid metabolism, being oxidized to oxaloacetate and oxidatively decarboxylated to pyruvate. Pyruvate can be aminated to alanine or converted to acetyl-CoA where it either enters the TCA cycle by condensation with oxaloacetate or forms polyhydroxybutyrate (PHB). Thus regulation of carbon and nitrogen metabolism are strongly connected. Efficient catabolism of C4-dicarboxylates requires the balanced input and removal of intermediates from the TCA cycle. The TCA cycle in bacteroids may be limited by the redox state of NADH/NAD+ at the 2-ketoglutarate dehydrogenase complex, and a number of pathways may be involved in bypassing this block. These pathways include PHB synthesis, glutamate synthesis, glycogen synthesis, GABA shunt and glutamine cycling. Their operation may be critical in maintaining the optimum redox poise and carbon balance of the TCA cycle. They can also be considered to be overflow pathways since they act to remove or add electrons and carbon into the TCA cycle. Optimum operation of the TCA cycle has a major impact on nitrogen fixation.

Alanine↗
PubMed2002

Biomaterial patches sutured onto the rat stomach induce a set of genes encoding pancreatic enzymes.

Asymmetric patches of polyhydroxybutyric acid with one smooth and one rough surface were produced by a dipping procedure. These patches were implanted into the rat gastrointestine and tissue samples were generated at distinct time intervals after surgery. The host's response towards the foreign material was analyzed by Differential Display and RNA profiles were compared to each other. One to two weeks after surgery a group of mRNAs encoding pancreatic enzymes was transiently present after biomaterial implantation.

Animals↗
PubMed2002

Effect of surface treatment on the biocompatibility of microbial polyhydroxyalkanoates.

The biocompatibility of microbial polyesters polyhydroxybutyrate (PHB) and poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) were evaluated in vitro. The mouse fibroblast cell line L929 was inoculated on films made of PHB, PHBHHx and their blends, polylactic acid (PLA) as control. It was found that the growth of the cells L929 was poor on PHB and PLA films. The viable cell number ranged from 8.8 x 10(2) to 1.8 x 10(4)/cm2 only. Cell growth on the films made by blending PHB and PHBHHx showed a dramatic improvement. The viable cell number observed increased from 9.7 x 10(2) to 1.9 x 10(5) on a series of PHB/PHBHHx blended film in ratios of 0.9/0.1:0/1, respectively, indicating a much better biocompatibility in the blends contributed by PHBHHx. Biocompatibility was also strongly improved when these polymers were treated with lipases and NaOH, respectively. However, the effects of treatment were weakened when PHBHHx content increased in the blends. It was found that lipase treatment had more increased biocompatibility than NaOH. After the treatment biocompatibility of PHB was approximately the same as PLA, while PHBHHx and its dominant blends showed improved biocompatibility compared to PLA.

Animals↗