补料培养提高真养产碱杆菌产3-羟基丁酸和3-羟基戊酸共聚物生产强度的研究

对Alcaligenes eutrophus进行高密度培养,研究表明在发酵过程中进行有效控制,可以较大幅度地提高3－羟基丁酸和3－羟基戊酸共聚物[P(3HB-co-3HV)]的生产强度。实验中选择使用限氮的方法积累P(3HB-co-3HV),分别采用丙酸和戊酸为3HV前体,对摇瓶种子生长状态,停氮时机对菌体生产P(3HB-co-3HV)的影响以及补酸（3HV前体）策略进行了研究,在6．6L罐中,以葡萄糖为碳源,以丙酸为3HV前体培养50h,细胞干重,PHA产量,PHA含量分别达到149．9g/L,149.9g/L,83.3%(其中3HV组分占PHA的12．4mol%),生产强度达到2．50（g.h^-1.L^-1);以戊酸为3HV前体培养45h,细胞干重,PHA产量,PHA含量分别达到160．2g/L,119.0g/L,74.2%（其中3HV组分占PHA的17．7mol%)生产强度达到2．64（g.h^-1.L^-1)。     

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by <Emphasis Type="Italic">Azotobacter chroococcum</Emphasis> strain 7B

The ability of Azotobacter chroococcum strain 7B, producer of poly(3-hydroxybutyrate) (PHB), to synthesize its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) was studied. It was demonstrated, for the first time, that A. chroococcum strain 7B was able to synthesize P(3HB-co-3HV) with various molar rates of HV in the polymer chain when cultivated on medium with sucrose and carboxylic acids as precursors of HV elements in the PHB chain, namely, valeric (13.1–21.6 mol %), propanoic (3.1 mol %), and hexanoic (2.1 mol %) acids. Qualitative and functional differences between PHB and P(3HB-co-3HV) were demonstrated by example of the release kinetic of methyl red from films made of synthesized polymers. Maximal HV incorporation into the polymer chain (28.8mol %) was recorded when the nutrient medium was supplemented with 0.1% peptone on the background of 20 mM valerate. These results suggest that that the studied strain can be regarded as a potential producer of not only PHB but also P(3HB-co-3HV).     

Sequential feeding of glucose and valerate in a fed-batch culture of Ralstonia eutropha for production of poly(hydroxybutyrate-co-hydroxyvalerate) with high 3-hydroxyvalerate fraction

Several important properties of poly(3-hydroxybutyric-co-3-hydroxyvaleric acids) (P(3HB-co-3HV) depend mainly on the HV unit fraction of the copolymer. Sequential and simultaneous feeding of glucose and valerate were employed to produce P(3HB-co-3HV) in a fed-batch culture of Ralstonia eutropha, and the effects of feeding models on the cell growth, 3HV unit fraction, and copolymer productivity have been investigated. The sequential feeding of glucose and then valerate resulted in a cell density of 110.2 g/L, 3HV unit fraction of 62.7 mol %, and copolymer productivity of 0.56 g/(L.h), while the latter simultaneous feeding strategy never achieved the 3HV fraction of P(3HB-co-3HV) higher than 50%. A nuclear magnetic resonance study confirmed that the production of random copolymer P(3HB-co-3HV) with high 3HV unit fraction was possible even with sequential feeding of glucose and valerate.     

High-level production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by fed-batch culture of recombinant Escherichia coli.

Fermentation strategies for production of high concentrations of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] with different 3-hydroxyvalerate (3HV) fractions by recombinant Escherichia coli harboring the Alcaligenes latus polyhydroxyalkanoate biosynthesis genes were developed. Fed-batch cultures of recombinant E. coli with the pH-stat feeding strategy facilitated production of high concentrations and high contents of P(3HB-co-3HV) in a chemically defined medium. When a feeding solution was added in order to increase the glucose and propionic acid concentrations to 20 g/liter and 20 mM, respectively, after each feeding, a cell dry weight of 120.3 g/liter and a relatively low P(3HB-co-3HV) content, 42.5 wt%, were obtained. Accumulation of a high residual concentration of propionic acid in the medium was the reason for the low P(3HB-co-3HV) content. An acetic acid induction strategy was used to stimulate the uptake and utilization of propionic acid. When a fed-batch culture and this strategy were used, we obtained a cell concentration, a P(3HB-co-3HV) concentration, a P(3HB-co-3HV) content, and a 3HV fraction of 141.9 g/liter, 88.1 g/liter, 62.1 wt%, and 15.3 mol%, respectively. When an improved nutrient feeding strategy, acetic acid induction, and oleic acid supplementation were used, we obtained a cell concentration, a P(3HB-co-3HV) concentration, a P(3HB-co-3HV) content, and a 3HV fraction of 203.1 g/liter, 158.8 g/liter, 78.2 wt%, and 10.6 mol%, respectively; this resulted in a high level of productivity, 2.88 g of P(3HB-co-3HV)/liter-h.     

Biosynthesis of poly(3-hydroxyalkanoate) from amino acids

It was found that an optically active copolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), denoted as P(3HB-co-3HV), is synthesized by Alcaligenes eutrophus H16 from several amino acids under various fermentation conditions. The optimum condition for the biosynthesis from one amino acid, threonine, was investigated and its biosynthetic pathway was discussed on the basis of the relation between the fermentation condition and the co-monomer composition of the produced polyesters.     

High-Level Production of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate) by Fed-Batch Culture of Recombinant Escherichia coli

Fermentation strategies for production of high concentrations of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] with different 3-hydroxyvalerate (3HV) fractions by recombinant Escherichia coli harboring the Alcaligenes latus polyhydroxyalkanoate biosynthesis genes were developed. Fed-batch cultures of recombinant E. coli with the pH-stat feeding strategy facilitated production of high concentrations and high contents of P(3HB-co-3HV) in a chemically defined medium. When a feeding solution was added in order to increase the glucose and propionic acid concentrations to 20 g/liter and 20 mM, respectively, after each feeding, a cell dry weight of 120.3 g/liter and a relatively low P(3HB-co-3HV) content, 42.5 wt%, were obtained. Accumulation of a high residual concentration of propionic acid in the medium was the reason for the low P(3HB-co-3HV) content. An acetic acid induction strategy was used to stimulate the uptake and utilization of propionic acid. When a fed-batch culture and this strategy were used, we obtained a cell concentration, a P(3HB-co-3HV) concentration, a P(3HB-co-3HV) content, and a 3HV fraction of 141.9 g/liter, 88.1 g/liter, 62.1 wt%, and 15.3 mol%, respectively. When an improved nutrient feeding strategy, acetic acid induction, and oleic acid supplementation were used, we obtained a cell concentration, a P(3HB-co-3HV) concentration, a P(3HB-co-3HV) content, and a 3HV fraction of 203.1 g/liter, 158.8 g/liter, 78.2 wt%, and 10.6 mol%, respectively; this resulted in a high level of productivity, 2.88 g of P(3HB-co-3HV)/liter-h.     

Enhanced production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by fed-batch cultures of Pseudomonas sp EL-2

Pseudomonas sp EL-2 was cultivated to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] from a structurally unrelated carbon source, glucose, by a fed-batch culture technique. Variation of the carbon to nitrogen (C/N) ratio of the medium produced optimal P(3HB-co-3HV) production at a C/N ratio of 95. Production of P(3HB-co-3HV) was favored by a dissolved oxygen tension of 40%. A maximum biomass concentration of 38 g L⁻¹ containing 53% P(3HB-co-3HV) was achieved after 45 h of cultivation. This corresponds to a volumetric productivity of 0.84 g L⁻¹ h⁻¹. The copolymer contained 7.5 mol% 3-hydroxyvalerate. Journal of Industrial Microbiology & Biotechnology (2000) 24, 36–40. Received 28 January 1999/ Accepted in revised form 11 September 1999     

Regulation of poly-(R)-(3-hydroxybutyrate-co-3-hydroxyvalerate) biosynthesis by the AtoSCDAEB regulon in phaCAB + Escherichia coli

AtoSC two-component system (TCS) upregulates the high-molecular weight poly-(R)-3-hydroxybutyrate (PHB) biosynthesis in recombinant phaCAB ⁺ Escherichia coli strains, with the Cupriavidus necator phaCAB operon. We report here that AtoSC upregulates also the copolymer P(3HB-co-3HV) biosynthesis in phaCAB ⁺ E. coli. Acetoacetate-induced AtoSC maximized P(3HB-co-3HV) to 1.27 g/l with a 3HV fraction of 25.5 % wt. and biopolymer content of 75 % w/w in a time-dependent process. The atoSC locus deletion in the ?atoSC strains resulted in 4.5-fold P(3HB-co-3HV) reduction, while the 3HV fraction of the copolymer was restricted to only 6.4 % wt. The ?atoSC phenotype was restored by extrachromosomal introduction of AtoSC. Deletion of the atoDAEB operon triggered a significant decrease in P(3HB-co-3HV) synthesis and 3HV content in ?atoDAEB strains. However, the acetoacetate-induced AtoSC in those strains increased P(3HB-co-3HV) to 0.8 g/l with 21 % 3HV, while AtoC or AtoS expression increased P(3HB-co-3HV) synthesis 3.6- or 2.4-fold, respectively, upon acetoacetate. Complementation of the ?atoDAEB phenotype was achieved by the extrachromosomal introduction of the atoSCDAEB regulon. Individual inhibition of β-oxidation and mainly fatty acid biosynthesis pathways by acrylic acid or cerulenin, respectively, reduced P(3HB-co-3HV) biosynthesis. Under those conditions, introduction of atoSC or atoSCDAEB regulon was capable of upregulating biopolymer accumulation. Concurrent inhibition of both the fatty acid metabolic pathways eliminated P(3HB-co-3HV) production. P(3HB-co-3HV) upregulation in phaCAB ⁺ E. coli by AtoSC signaling through atoDAEB operon and its participation in the fatty acids metabolism interplay provide additional perceptions of AtoSC critical involvement in E. coli regulatory processes towards biotechnologically improved polyhydroxyalkanoates biosynthesis.     

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and characterisation of its blend with oil palm empty fruit bunch fibers

Poly(3-hydroxybutyrate-co-38 mol%-3-hydroxyvalerate) [P(3HB-co-38mol%-3HV)] was produced by Cupriavidus sp. USMAA2-4 in the presence of oleic acid and 1-pentanol. Due to enormous production of empty fruit bunch (EFB) in the oil palm plantation and high production cost of P(3HB-co-3HV), oil palm EFB fibers were used for biocomposites preparation. In this study, maleic anhydride (MA) and benzoyl peroxide (DBPO) were used to improve the miscibility between P(3HB-co-3HV) and EFB fibers. Introduction of MA into P(3HB-co-3HV) backbone reduced the molecular weight and improved the thermal stability of P(3HB-co-3HV). Thermal stability of P(3HB-co-3HV)/EFB composites was shown to be comparable to that of commercial packaging product. Composites with 35% EFB fibers content have the highest tensile strength compared to 30% and 40%. P(3HB-co-3HV)/EFB blends showed less chemicals leached compared to commercial packaging.     

Accumulation of PHA and its copolyesters by Methylobacterium sp. KCTC 0048

Summary Methylobacterium sp. KCTC 0048 isolated from soil, could synthesize a variety of copolyesters when secondary carbon substrates were added to nitrogen-limited cultures containing methanol as a major carbon and energy source. The copolyester of 3-hydroxy-butyrate and 3-hydroxyvalerate, P(3HB-co-3HV) accumulated when valeric acid, pentanol or heptanoic acid was added to the nitrogen-limited medium containing methanol. The copolyester of 3-hydroxybutyrate and 4-hydroxybutyrate, P(3HB-co-4HB) was synthesized from 4-hydroxybutyrate, 1,4-butanediol, or -butyrolactone, and the copolyester of 3-hydroxybutyrate and 3-hydroxypropionate (P(3HB-co-3HP)), from 3-hydroxypropionate as the secondary carbon substrates, respectively.     

Biosynthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) by metabolically engineered Escherichia coli strains

The recombinant Escherichia coli strain, equipped with the newly cloned Aeromonas PHA biosynthesis genes, could produce a terpolymer of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 3-hydroxyhexanoate (3HHx) [P(3HB-co-3HV-co-3HHx)] from dodecanoic acid plus odd carbon number fatty acid. In addition, the orf1 gene of Aeromonas hydrophila was found to play a critical role in assimilating the 3HV monomer and in regulating the monomer fraction in the terpolymer.     

Propionic acid metabolism and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (P3HB-co-3HV) production by Burkholderia sp

Mutants of Burkholderia sp. that are unable to grow on propionic acid (prp) but still accumulate P3HB-co-3HV from carbohydrate and propionic acid were studied. In shaken flask tests, yields of 3HV from propionic acid (Y(3HV/Prop)) increased from 0.10 g g(-1) in the wild type to c.a. 0.35 g g(-1) in mutants affected in alpha-oxidation pathway or to 0.80 g g(-1) in mutants not affected in that pathway. In bioreactor tests, mutant IPT 189 showed Y(3HV/Prop) = 1.20 g g(-1), a yield very close to the theoretical maximum of 1.35 g g(-1). Accumulation of 3HV units from unrelated carbon sources was undetectable in these mutants indicating that 3HV units are produced directly from propionic acid. Thus, the industrial use of those mutants to produce the copolymer from sucrose and propionic acid could significantly reduce the production costs. The results strongly suggest the existence of at least two pathways that are involved in the oxidation of propionic acid in Burkholderia sp. Their rates would be modulated by the availability of propionic acid.     

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.     

Synthesis of biodegradable polyesters by Gram negative bacterium isolated from Malaysian environment

A locally isolated Gram negative bacterium, Cupriavidus sp. USMAA9-39 was able to produce various types of biodegradable polyesters through a two-step cultivation process. These are copolymer poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)], copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] and terpolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxybutyrate) [P(3HB-co-3HV-co-4HB)]. These polymers were synthesized by this bacterium when grown with a combination of some carbon sources. The biosynthesis of P(3HB-co-4HB) was achieved by using carbon sources such as γ-butyrolactone or 1,4-butanediol or by a combination of oleic acid with either γ-butyrolactone or 1,4-butanediol. Meanwhile, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was produced using 1-pentanol or valeric acid or by a combination of oleic acid with either 1-pentanol or valeric acid. When γ-butyrolactone or 1,4-butanediol with either valeric acid or 1-pentanol were used as mixed carbon sources, P(3HB-co-3HV-co-4HB) terpolymer were produced. The presence of 3HB, 3HV or/and 4HB monomers were confirmed by gas chromatography and nuclear magnetic resonance (NMR) spectroscopy.     

n-Amyl alcohol as a substrate for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by bacteria

Abstract n -Amyl alcohol was examined as a source for the synthesis of the 3-hydroxyvalerate (3HV) unit of the biopolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)), by Alcaligenes sp., Pseudomonas sp. and several methylotrophic bacteria. A. eutrophus and Ps. lemoignei synthesized P(3HB-co-3HV) from glucose and n -amyl alcohol under nitrogen-deficient conditions. Many of methylotrophic bacteria grown on methanol synthesized the copolyester from methanol and n -amyl alcohol under nitrogen-deficient conditions. The content and composition of the polyester varied from strain to strain. Paracoccus denitrificans differed from all others in having a higher content of 3-hydroxyvalerate units in the copolyester synthesized.     

Comparative evaluation of physico-chemical characteristics of biopolyesters P(3HB) and P(3HB-co-3HV) produced by endophytic <Emphasis Type="Italic">Bacillus cereus</Emphasis> RCL 02

Background

Bacteria endogenously residing within the plant tissues have attracted significant attention for production of biopolyester, polyhydroxyalkanoates (PHAs). Bacillus cereus RCL 02 (MCC 3436), a leaf endophyte of oleaginous plant Ricinus communis L. accumulates 81% poly(3-hydroxybutyrate) [P(3HB)] of its cell dry biomass when grown in mineral salts (MS) medium.

Methods

The copolymer production efficiency of B. cereus RCL 02 was evaluated in valeric acid supplemented MS medium under biphasic cultivation condition. The copolymer so produced has been compared with the P(3HB) isolated from RCL 02 in terms of thermal, mechanical and chemical properties.

Results

Valeric acid supplementation as co-substrate in the medium has led to the production of copolymer of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) [P(3HB-co-3HV)] with 14.6 mol% 3HV. The identity of the polymers has been confirmed by X-ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic studies. Thermogravimetric analysis (TGA) revealed that P(3HB) and P(3HB-co-3HV) films degraded at 278.66°C and 273.49°C, respectively. The P(3HB-co-3HV) showed lower melting temperature (165.03°C) compared to P (3HB) (170.74°C) according to differential scanning calorimetry (DSC). Incorporation of 3HV monomers decreased the tensile strength (21.52 MPa), tensile modulus (0.93 GPa), storage modulus (E′) (0.99 GPa) and increased % elongation at break (12.2%) of the copolyester. However, P(3HB) showed better barrier properties with lower water vapor transmission rate (WVTR) of 0.55 g-mil/100 in²/24 h.

Conclusion

These findings emphasized exploration of endophytic bacterial strain (RCL 02) to produce biodegradable polyesters which might have significant potential for industrial application.

     

Production and characterization of poly-beta-hydroxyalkanoate copolymers from Burkholderia cepacia utilizing xylose and levulinic acid

Poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (P(3HB-co-3HV)) copolymers were prepared via shake-flask fermentations of Burkholderia cepacia (formerly Pseudomonas cepacia) containing 2.2% (w/v) xylose and concentrations of levulinic acid ranging from 0.07% to 0.67% (w/v). Periodic harvest of shake-flask cultures from 48 to 92 h post-inoculation yielded 4.4-5.3 g/L of dry cell biomass, containing 42-56% (w/w) P(3HB-co-3HV), with optimal product yield occurring between 66 and 74 h. Growth and PHA accumulation enhancement were observed with concentrations of levulinic acid from 0.07 to 0.52% (w/v), producing dry cell biomass and P(3HB-co-3HV) yields of 9.5 and 4.2 g/L, respectively, at the 0.52% (w/v) concentration of levulinic acid. Representative samples were subjected to compositional analysis by 300 MHz 1H and 150 MHz 13C NMR, indicating that these random copolymers contained between 0.8 and 61 mol % 3-hydroxyvalerate (3HV). Solvent-cast film samples were characterized by differential scanning calorimetry, which demonstrated melting temperatures (Tm) to decrease in a pseudoeutectic fashion from 174.3 degrees C (0.8 mol % 3HV) to a minimum of 154.2 degrees C (25 mol % 3HV) and the glass transition temperatures (Tg) to decrease linearly from 2.1 to -11.9 degrees C as a function of increasing mol % 3HV. Thermogravimetric analysis of the copolymer series showed the temperature for onset of thermal decomposition (T(decomp)) to vary as a function of mol % 3HV from 273.4 to 225.5 degrees C. Intrinsic viscosities (eta) varied from 3.2 to 5.4 dL/g, as determined by dilute solution viscometry. Viscosity average molecular weights (Mv) of the copolymers were determined to range from 469 to 919 kDa, indicating that these P(3HB-co-3HV) copolymers are of sufficient molecular mass for commercial application.     

Estimation of the Number of Polyhydroxyalkanoate (PHA)-Degraders in Soil and Isolation of Degraders Based on the Method of Most Probable Number (MPN) Using PHA-Film

A new method to estimate the number of polyhydroxyalkanoates (PHA)-degraders in soil and to isolate degraders, called the film-MPN method, is proposed. The incubation time was measured by the first order reaction (FOR) model. This method was used to estimate numbers of poly (3-hydroxybutyrate-co-3-hydroxyvalerate)[P(3HB-co-3HV)]- and poly(3-hydroxyvalerate-co-4-hydroxybutyrate)[P(3HB-co-4HB)]-degraders in garden soil (4.30 × 10⁵ and 2.15 × 10⁵ aerobic degraders per gram of dry soil, respectively). The number of P(3HB-co-3HV)-degraders in paddy field soil was 5.06 × 10⁵ aerobic degraders per gram dry soil. Also, several P(3HB-co-3HV)-degraders were isolated directly from positive-growth tubes of high dilution.     

Production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with high molar fractions of 3-hydroxyvalerate by a threonine-overproducing mutant of Alcaligenes sp. SH-69

A threonine overproducing mutant of Alcaligenes sp. SH-69 was isolated and its ability to produce poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3HB-co-3HV), was investigated. The 3HV fraction in poly(3HB-co-3HV) produced from glucose as the sole carbon source exceeded 22 mol%, which is approximately six times higher than that achieved by the wild type under the same culture conditions. Furthermore, the addition of a relatively low concentration (10 mM) of propionic acid, valeric acid or levulinic acid to the glucose medium greatly increased the molar fraction of 3HV in the copolyester, to 38–77 mol%. The results suggest that metabolic engineering of the biosynthetic pathways supplying polyhydroxyalkanoate monomers, such as the threonine biosynthetic pathway, can lead to new poly(3HB-co-3HV)-producing strains.     

A novel <Emphasis Type="Italic">Bacillus</Emphasis> sp. accumulating poly (3-hydroxybutyrate-co-3-hydroxyvalerate) from a single carbon substrate

The objective of this paper was to report a bacterium designated as 88D, capable of producing poly (3-hydroxybutyrate-co-3-hydroxyvalerate) [P (3HB-co-3HV)] copolymer from a single carbon source, which was isolated from a municipal sewage treatment plant in Hyderabad, India. This microorganism, based on the phenotypical features and genotypic investigations, was identified as Bacillus sp. The optimal growth of Bacillus sp. 88D occurred between 28 and 30°C and at pH 7. The strain yielded a maximum of 64.62% dry cell weight (DCW) polymer in the medium containing glucose as carbon source, which was followed by 60.46% DCW polymer in glycerol containing medium. Bacillus sp. 88D produced P (3HB-co-3HV) from glucose or glycerol, when they were used as a single carbon substrate. This bacterium produced polyhydrxybutyrate (PHB) when sodium acetate was used as sole carbon substrate. The viscosity average molecular mass (Mv) of the copolymers ranged from 523 to 627 kDa. The physical, chemical and mechanical properties of the biopolymers were characterized.