Biosynthesis and characterization of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) in Alcaligenes eutrophus

Copolyesters of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) were produced by Alcaligenes eutrophus at 30 degrees C in nitrogen-free culture solutions containing gamma-butyrolactone alone or with fructose or butyric acid as the carbon sources. When gamma-butyrolactone was used as the sole carbon source, the 4HB fraction in copolyester increased from 9 to 21 mol% as the concentration of gamma-butyrolactone in the culture solution increased from 10 to 25 g/l. The addition of fructose to the culture solution of gamma-butyrolactone resulted in a decrease in the 4HB fraction in copolyester. The copolyesters produced from gamma-butyrolactone and fructose by A. eutrophus were shown to have random sequence distribution of 3HB and 4HB units by analysis of the 125 MHz 13C n.m.r. spectra. In contrast, a mixture of random copolyesters with two different 4HB fractions was produced by A. eutrophus when gamma-butyrolactone and butyric acid were used as the carbon sources. These results are discussed on the basis of a proposed biosynthetic pathway of P(3HB-co-4HB). The copolyester films became soft with an increase in the 4HB fraction, and the elongation to break at 23 degrees C increased from 5 to 444% as the 4HB fraction increased from 0 to 16 mol%. The P(3HB-co-10% 4HB) film was shown to be biodegradable in an activated sludge.     

Degradation of poly (3-hydroxybutyrate) and its copolymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate) by a marine Streptomyces sp. SNG9.

A marine Streptomyces sp. SNG9 was characterized by its ability to utilize poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate P (3HB-co-HV). The bacterium grew efficiently in a simple mineral liquid medium enriched with 0.1% poly(3-hydroxybutyrate) powder as the sole carbon source. Cells excreted PHB depolymerase and degraded the polymer particles to complete clarity in 4 days. The degradation activity was detectable by the formation of a clear zone around the colony (petri plates) or a clear depth under the colony (test tubes). The expression of PHB depolymerase was repressed by the presence of simple soluble carbon sources. Bacterial degradation of the naturally occurring sheets of poly(3-hydroxybutyrate) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was observed by scanning electron microscopy (SEM). Morphological alterations of the polymers sheets were evidence for bacterial hydrolysis.     

Production of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by Ralstonia eutropha from soybean oil

High-yield production of polyhydroxyalkanoates (PHAs) by Ralstonia eutropha KCTC 2662 was investigated using soybean oil and γ-butyrolactone as carbon sources. In flask culture, it was shown that R. eutropha KCTC 2662 accumulated PHAs during the growth phase. The optimum carbon to nitrogen ratio (C/N ratio) giving the highest cell and PHA yield was 20 g-soybean oil/g-(NH(4))(2)SO(4). The 4-hydroxybutyrate (4HB) fraction in the copolymer was not strongly affected by the C/N ratio. In a 2.5-L fermentor, a homopolymer of poly(3-hydroxybutyrate) [P(3HB)] was produced from soybean oil as the sole carbon source by batch and fed-batch cultures of R. eutropha with dry cell weights of 15-32 g/L, PHA contents of 78-83 wt% and yields of 0.80-0.82 g-PHA/g-soybean oil used. By co-feeding soybean oil and γ-butyrolactone as carbon sources, a copolymer of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] could be produced with dry cell weights of 10-21 g/L, yields of 0.45-0.56 g-PHA/g-soybean oil used (0.39-0.50g-PHA/g-carbon sources used) and 4HB fractions of 6-10 mol%. Higher supplementation of γ-butyrolactone increased the 4HB fraction in the copolymer, but decreased cell and PHA yield.     

Microbial production of 4-hydroxybutyrate,poly-4-hydroxybutyrate,and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by recombinant microorganisms

4-Hydroxybutyrate (4HB) was produced by Aeromonas hydrophila 4AK4, Escherichia coli S17-1, or Pseudomonas putida KT2442 harboring 1,3-propanediol dehydrogenase gene dhaT and aldehyde dehydrogenase gene aldD from P. putida KT2442 which are capable of transforming 1,4-butanediol (1,4-BD) to 4HB. 4HB containing fermentation broth was used for production of homopolymer poly-4-hydroxybutyrate [P(4HB)] and copolymers poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-4HB)]. Recombinant A. hydrophila 4AK4 harboring plasmid pZL-dhaT-aldD containing dhaT and aldD was the most effective 4HB producer, achieving approximately 4 g/l 4HB from 10 g/l 1,4-BD after 48 h of incubation. The strain produced over 10 g/l 4HB from 20 g/l 1,4-BD after 52 h of cultivation in a 6-L fermenter. Recombinant E. coli S17-1 grown on 4HB containing fermentation broth was found to accumulate 83 wt.% of intracellular P(4HB) in shake flask study. Recombinant Ralstonia eutropha H16 grew to over 6 g/l cell dry weight containing 49 wt.% P(3HB-13%4HB) after 72 h.     

Degradation of poly (3-hydroxybutyrate) and its copolymer poly (3-hydroxybutyrate-co-3-hydroxyvalerate) by a marine Streptomyces sp. SNG9

A marine Streptomyces sp. SNG9 was characterized by its ability to utilize poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate P (3HB-co-HV). The bacterium grew efficiently in a simple mineral liquid medium enriched with 0.1% poly(3-hydroxybutyrate) powder as the sole carbon source. Cells excreted PHB depolymerase and degraded the polymer particles to complete clarity in 4 days. The degradation activity was detectable by the formation of a clear zone around the colony (petri plates) or a clear depth under the colony (test tubes). The expression of PHB depolymerase was repressed by the presence of simple soluble carbon sources. Bacterial degradation of the naturally occurring sheets of poly(3-hydroxybutyrate) and its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was observed by scanning electron microscopy (SEM). Morphological alterations of the polymers sheets were evidence for bacterial hydrolysis.     

Production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) byPseudomonas acidovorans

Summary Terpolyesters of 3-hydroxybutyrate (3HB), 4-hydroxybutyrate (4HB) and 3-hydroxyvarelate (3HV) were produced byPseudomonas acidovorans in nitrogen-free culture solutions of 1,4-butanediol and pentanol. When 1,4-butanediol was used as the sole carbon source, a polyester with an unusually high 4HB fraction of 99 mol% was produced.     

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from structurally unrelated single carbon sources by newly isolated Pseudomonas sp. EL-2

Summary A Pseudomonas sp. EL-2 strain capable of synthesizing poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] was isolated from activated sludge. For simulation of P(3HB-co-3HV) production in the cells, deficiency of nutrients such as NH₄ ⁺, SO₄ ^2- and Mg²⁺ was crucial and the maximum content of P(3HB-co-3HV) could reach 46% on NH₄ ⁺-deficient medium. This organism synthesized P(3HB-co-3HV) with 3HV monomer in the range from 1.9 to 49.3 mol% from unrelated single carbon sources such as glucose, fructose, propionate, or sorbitol. P(3HB-co-3HV)s containing a higher fraction of 3HV were produced by adding propionic acid to glucose medium.     

Biosynthesis of poly(3-hydroxybutyrate) (PHB) by Cupriavidus necator H16 from jatropha oil as carbon source

Poly(3-hydroxybutyrate) (PHB) is a biodegradable polymer that can be synthesized through bacterial fermentation. In this study, Cupriavidus necator H16 is used to synthesize PHB by using Jatropha oil as its sole carbon source. Different variables mainly jatropha oil and urea concentrations, and agitation rate were investigated to determine the optimum condition for microbial fermentation in batch culture. Based on the results, the highest cell dry weight and PHB concentrations of 20.1 and 15.5 g/L, respectively, were obtained when 20 g/L of jatropha oil was used. Ethanol was used as external stress factor and the addition of 1.5 % ethanol at 38 h had a positive effect with a high PHB yield of 0.987 g PHB/g jatropha oil. The kinetic studies for cell growth rate and PHB production were conducted and the data were fitted with Logistic and Leudeking–Piret models. The rate constants were evaluated and the theoretical values were in accordance with the experimental data obtained.     

Structure and properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) produced by Alcaligenes latus

Summary Random copolymers of 3-hydroxybutyrate (3HB) and 4-hydroxybutyrate (4HB) with a wide range of compositions varying from 0 to 83 mol% 4HB were produced by Alcaligenes latus from the mixed carbon substrates of 3-hydroxybutyric and 4-hydroxybutyric acids. The structure and physical properties of P(3HB-co-4HB) were characterized by¹H and¹³C NMR spectroscopy, gel-permeation chromatography, and differential scanning calorimetry. The isothermal radial growth rates of spherulites of P(3HB-co-4HB) were much slower than the rate of P(3HB) homopolymer. The enzymatic degradation rates of P(3HB-co-4HB) films by a PHB depolymerase were strongly influenced by the copolymer composition.     

Production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) from unrelated carbon sources by metabolically engineered Escherichia coli

A metabolically engineered Escherichia coli has been constructed for the production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] from unrelated carbon sources. Genes involved in succinate degradation in Clostridium kluyveri and P(3HB) accumulation pathway of Ralstonia eutropha were co-expressed for the synthesis of the above copolyester. E. coli native succinate semialdehyde dehydrogenase genes sad and gabD were both deleted for eliminating succinate formation from succinate semialdehyde, which functioned to enhance the carbon flux to 4HB biosynthesis. The metabolically engineered E. coli produced 9.4 g l^?1 cell dry weight containing 65.5% P(3HB-co-11.1 mol% 4HB) using glucose as carbon source in a 48 h shake flask growth. The presence of 1.5–2 g l^?1 α-ketoglutarate or 1.0 g l^?1 citrate enhanced the 4HB monomer content from 11.1% to more than 20%. In a 6 l fermentor study, a 23.5 g l^?1 cell dry weight containing 62.7% P(3HB-co-12.5 mol% 4HB) was obtained after 29 h of cultivation. To the best of our knowledge, this study reports the highest 4HB monomer content in P(3HB-co-4HB) produced from unrelated carbon sources.     

Characterization of poly(3-hydroxybutyrate) produced by Cupriavidus necator in solid-state fermentation

Solid-state fermentation (SSF) has recently been proposed as an alternative to submerged fermentation for the production of poly(hydroxyalkanoates). In the present work, X-ray diffraction, differential scanning calorimetry, nuclear magnetic resonance and infrared spectroscopy were employed to investigate the chemical structure, as well as the thermal properties and the crystalline morphology of poly(3-hydroxybutyrate) samples produced by SSF, using as raw material either soy cake or soy cake supplemented with 2.5% (m/m) sugarcane molasses. The results obtained showed that the biopolymer obtained by SSF presented the same properties as commercial PHB, except for the higher molar mass and the lower degree of crystallinity that were observed. Thus, the present data indicate that solid-state fermentation is an interesting alternative for the production of PHB, allowing the production of biopolymers with adequate properties from low-cost, renewable resources.     

Microbial degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in soils

[This corrects the article on p. 3236 in vol. 59.].     

Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) formation from gamma-aminobutyrate and glutamate

To provide 4-hydroxybutyryl-CoA for poly(3-hydroxybutyrate-co-4-hydroxybutyrate) formation from glutamate in Escherichia coli, an acetyl-CoA:4-hydroxybutyrate CoA transferase from Clostridium kluyveri, a 4-hydroxybutyrate dehydrogenase from Ralstonia eutropha, a gamma-aminobutyrate:2-ketoglutarate transaminase from Escherichia coli, and glutamate decarboxylases from Arabidopsis thaliana or E. coli were cloned and functionality tested by expression of single genes in E. coli to verify enzymatic activity, and uniquely assembled as operons under the control of the lac promoter. These operons were independently transformed into E. coli CT101 harboring the runaway replication vector pJM9238 for polyhydroxyalkanoate (PHA) production. Plasmid pJM9238 contains the PHA biosynthetic operon of R. eutropha under tac promoter control. Polyhydroxyalkanoate formation was monitored by nuclear magnetic resonance (NMR) spectroscopic analysis of the chloroform extracted and ethanol precipitated polyesters. Functionality of the biosynthetic pathway for copolymer production was demonstrated through feeding experiments using various carbon sources that supplied different precursors within the 4HB-CoA biosynthetic pathway.     

Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers

In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 x 10(5) to 6.65 x 10(5), were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state (1)H NMR data were used to determine polymer composition-of-matter, while solution-state (13)C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB-co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB-co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB-co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.     

In vitro biocompatibility of electrospun poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) fiber mats

In the present contribution, the potential for use of the ultrafine electrospun fiber mats of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) as scaffolding materials for skin and nerve regeneration was evaluated in vitro using mouse fibroblasts (L929) and Schwann cells (RT4-D6P2T) as reference cell lines. Comparison was made with PHB and PHBV films that were prepared by solution-casting technique. Indirect cytotoxicity assessment of the as-spun PHB and PHBV fiber mats with mouse fibroblasts (L929) and Schwann cells (RT4-D6P2T) indicated that the materials were acceptable to both types of cells. The attachment of L929 on all of the fibrous scaffolds was significantly better than that on both the film scaffolds and tissue-culture polystyrene plate (TCPS), while RT4-D6P2T appeared to attach on the flat surfaces of TCPS and the film scaffolds much better than on the rough surfaces of the fibrous scaffolds. For L929, all of the fibrous scaffolds were superior in supporting the cell proliferation to the film counterparts, but inferior to TCPS at days 3 and 5, while, for RT4-D6P2T, the rough surfaces of the fibrous scaffolds appeared to be very poor in supporting the cell proliferation when comparing with the smooth surfaces of TCPS and the film scaffolds. Scanning electron microscopy was also used to observe the behavior of both types of cells that were cultured on both the fibrous and the film scaffolds and glass substrate for 24 h.     

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) depolymerase from Aspergillus sp. NA-25

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) degrading thermophilic fungus was isolated from soil sample collected from waste disposal site, Islamabad, Pakistan. It was able to grow efficiently on a medium containing PHBV as a sole source of carbon and has been identified as Aspergillus sp. NA-25 by 18S rRNA. Using 9% of inoculum maximum production of PHBV depolymerase was observed at 45°C, pH 7.0 in the presence of 0.2% lactose as an additional carbon source. PHBV depolymerase was purified by precipitation with 80% ammonium sulfate and gel filtration chromatography on Sephadex G-75. The four enzyme forms obtained after gel filtration were analyzed on SDS-PAGE and their molecular weights (36, 68, 72 and 90 kDa) were determined. They were characterized on the basis of effect of different temperatures, pH, metal ions and different reagents on the PHBV activity and stability. It is obvious that the fungal strain Aspergillus sp. NA-25 is capable of degrading PHBV with the help of different types of depolymerases.     

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyalkanoates) by recombinant bacteria expressing the PHA synthase gene phaC1 from Pseudomonas sp. 61-3

Pseudomonas sp. 61-3 accumulated a blend of poly(3-hydroxybutyrate) [P(3HB)] homopolymer and a random copolymer consisting of 3-hydroxyalkanoate (3HA) units of 4–12 carbon atoms. The genes encoding β-ketothiolase (PhbA_Re) and NADPH-dependent acetoacetyl-CoA reductase (PhbB_Re) from Ralstoniaeutropha were expressed under the control of promoters for Pseudomonas sp. 61-3 pha locus or R. eutropha phb operon together with phaC1 _Ps gene (PHA synthase 1 gene) from Pseudomonas sp. 61-3 in PHA-negative mutants P. putida GPp104 and R. eutropha PHB⁻4 to produce copolyesters [P(3HB-co-3HA)] consisting of 3HB and medium-chain-length 3HA units of 6–12 carbon atoms. The introduction of the three genes into GPp104 strain conferred the ability to synthesize P(3HB-co-3HA) with relatively high 3HB compositions (up to 49 mol%) from gluconate and alkanoates, although 3HB units were not incorporated at all or at a very low fraction (3 mol%) into copolyesters by the strain carrying phaC1 _Ps gene only. In addition, recombinant strains of R. eutropha PHB⁻4 produced P(3HB-co-3HA) with higher 3HB fractions from alkanoates and plant oils than those from recombinant GPp104 strains. One of the recombinant strains, R. eutropha PHB⁻4/pJKSc46-pha, in which all the genes introduced were expressed under the control of the native promoter for Pseudomonas sp. 61-3 pha locus, accumulated P(3HB-co-3HA) copolyester with a very high 3HB fraction (85 mol%) from palm oil. The nuclear magnetic resonance analyses showed that the copolyesters obtained here were random copolymers of 3HB and 3HA units. Received: 12 July 1999 / Received revision: 1 October 1999 / Accepted: 2 October 1999     

Production of 3-hydroxypropionate homopolymer and poly(3-hydroxypropionate-co-4-hydroxybutyrate) copolymer by recombinant Escherichia coli

Conversion of 3-hydroxypropionate (3HP) from 1,3-propanediol (PDO) was improved by expressing dehydratase gene (dhaT) and aldehyde dehydrogenase gene (aldD) of Pseudomonas putida KT2442 under the promoter of phaCAB operon from Ralstonia eutropha H16. Expression of these genes in Aeromonas hydrophila 4AK4 produced up to 21 g/L 3HP in a fermentation process. To synthesize homopolymer poly(3-hydroxypropionate) (P3HP), and copolymer poly(3-hydroxypropionate-co-3-hydroxybutyrate) (P3HP4HB), dhaT and aldD were expressed in E. coli together with the phaC1 gene encoding polyhydroxyalkanoate (PHA) synthase gene of Ralstonia eutropha, and pcs' gene encoding the ACS domain of the tri-functional propionyl-CoA ligase (PCS) of Chloroflexus aurantiacus. Up to 92 wt% P3HP and 42 wt% P3HP4HB were produced by the recombinant Escherichia coli grown on PDO and a mixture of PDO+1,4-butanediol (BD), respectively.     

Biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) produced by Burkholderia cepacia D1.

Copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) were produced by Burkholderia cepacia D1 at 30°C in nitrogen-free culture solutions containing n-butyric acid and/or n-valeric acid. When n-valeric acid was used as the sole carbon source, the 3HV fraction in copolyester increased from 36 to 90 mol% as the concentration of n-valeric acid in the culture solution increased from 1 to 20 g/l. The addition of n-butyric acid to the culture solution resulted in a decrease in the 3HV fraction in copolyester. The copolymers biosynthesized by this method were mixtures of random copolymers having a wide variety of composition of the 3HV component. The melting points of the fractionated copolymers show a concave curve with the minimum at the 3HV content of ≈40 mol%. The a-parameter of lattice indices of the P(3HB) crystal for the fractionated copolymers largely increased as the 3HV composition increased. Biodegradability of the copolymer increased with the lower content of 3HV composition and/or the lower crystallinity.