Hydroxyalkanoates Research Articles

Potato Peel Waste as an Economic Feedstock for PHA Production by Bacillus circulans.

Polymers of hydroxy alkanoates (PHA), also known as biodegradable, biocompatible plastic, are potential alternatives to petrochemical-based plastics. PHA is synthesized by microbes in their cytoplasm in the form of inclusion bodies in stress conditions such as nitrogen, oxygen, and phosphorus with excessive amounts of carbon. Sugar extracted from potato peel in the form of hydrolysate was employed as a carbon source for PHA production after acidic hydrolysis. The acid hydrolysis conditions are optimized for dilute acid concentrations and temperatures. The highest sugar-yielding condition (2% 15min at 121 ℃) was used for submerged fermentation for PHA production by Bacillus circulans MTCC 8167. Fourier transform infrared spectroscopy, nuclear magnetic resonance, and differential scanning calorimetry were used for polymer characterization. Gas chromatography coupled with mass spectrometry confirmed the monomers such as hexadecenoic acid 3-hydroxy, methyl esters, pentadecanoic acid 14 methyl esters, and tetradecanoic acid 12- methyl esters. Crotonic acid assay was used for quantification of PHA and it was found highest (0.232 ± 0.04g/L) at 37°C and 36h of incubation. Hence, potato peel waste could be a potential feedstock for waste to valuable production.

Glucose metabolism in Pseudomonas aeruginosa is cyclic when producing Polyhydroxyalkanoates and Rhamnolipids

Pseudomonas aeruginosa is an important chassis for production of polyhydroxyalkanoates (PHA) and rhamnolipids (RHL). Advances in the understanding of the biosynthesis metabolism of these biocompounds are crucial for increasing yield. 13C-Metabolic Flux Ratio Analysis (13C-MFA) is a technique to estimate in vivo metabolic fluxes ratios. PHA and RHL are essentially non-growth associated products of biotechnological interest and both contain hydroxyalkanoates (HAs), whose labeling patterns could be accessed by GC-MS. In this study, to reveal the relative contributions of the Entner-Doudoroff (ED) pathway and the non-oxidative Pentose Phosphate (PP) pathway to PHA and RHL production, 13C-MFA was performed in Pseudomonas aeruginosa LFM634 when supplied with labeled glucose. This bacterial strain lacks both functional EMP and the oxidative PP branch. Labeling patterns in HAs were measured. Experiments with [U-13C] glucose indicated a low flux though PP pathway. An optimal design of labeling experiment showed that [6-13C] glucose would be the best substrate to enable an estimation of the ED flux with high accuracy. Results of experiments performed with this isotope indicated that about two-thirds of glyceraldehyde 3-phosphate is recycled through a cyclic ED architecture, suggesting that P. aeruginosa utilizes that cycle to regulate the NADPH/Acetyl-CoA ratio for PHA and RHL biosynthesis.

Gas Transport Phenomena and Polymer Dynamics in PHB/PLA Blend Films as Potential Packaging Materials.

Actually, in order to replace traditional fossil-based polymers, many efforts are devoted to the design and development of new and high-performance bioplastics materials. Poly(hydroxy alkanoates) (PHAS) as well as polylactides are the main candidates as naturally derived polymers. The intention of the present study is to manufacture fully bio-based blends based on two polyesters: poly (3-hydroxybutyrate) (PHB) and polylactic acid (PLA) as real competitors that could be used to replace petrol polymers in packaging industry. Blends in the shape of films have been prepared by chloroform solvent cast solution methodology, at different PHB/PLA ratios: 1/0, 1/9, 3/7, 5/5, 0/1. A series of dynamic explorations have been performed in order to characterize them from a different point of view. Gas permeability to N2, O2, and CO2 gases and probe (TEMPO) electron spin resonance (ESR) analyses were performed. Blend surface morphology has been evaluated by Scanning Electron Microscopy (SEM) while their thermal behavior was analyzed by Differential Scanning Calorimetry (DSC) technique. Special attention was devoted to color and transparency estimation. Both probe rotation mobility and N2, O2, and CO2 permeation have monotonically decreased during the transition from PLA to PHB, for all contents of bio-blends, namely because of transferring from PLA with lower crystallinity to PHB with a higher one. Consequently, the role of the crystallinity was elucidated. The temperature dependences for CO2 permeability and diffusivity as well as for probe correlation time allowed the authors to evaluate the activation energy of both processes. The values of gas transport energy activation and TEMPO rotation mobility are substantially close to each other, which should testify that polymer segmental mobility determines the gas permeability modality.

Commercialization of bacterial cell factories for the sustainable production of polyhydroxyalkanoate thermoplastics: progress and prospects.

Ubiquitous conventional plastics, generally manufactured from finite, nonsustainable fossil fuels are non-biodegradable wonder entities but their ill effect on Mother Nature has subsequently raised major environmental concerns like their safe disposal, solid waste management and several potential hazards. Such concerns have fuelled initiatives for research globally towards development of sustainable and eco-friendly bioplastics. The new generation of plastics called 'bioplastics' are polymers of long chain of repeating monomer units that are classified as photodegradable, semi-biodegradable, chemically synthesized and polyhydroxyalkanoates (PHAs). The commonly emerged novel bioplastics are polyesters of hydroxyalkanoates (HAs) called PHAs, which are lipoidic storage materials found in the cytosol of vast and diverse forms of bacteria. Among 150 different PHAs known so far, poly- 3-hydroxybutyrate is the most common and comprehensively characterized PHA. Interestingly, PHAs are only completely biodegradable plastics with material properties comparable to conventional plastics that can be achieved by regulating the co-monomers incorporation into PHAs backbone. PHA bioplastics are exploited in the form of user-friendly goods viz. films, absorbable sutures, bone plates, drug carriers, etc. Besides advantages, such useful entity(s) has major shortcomings as well like high production cost compared to conventional plastics. Precisely, in PHAs production, about fifty percent of the overall price is due to the carbon substrates. Consequently, exploring novel cost-effective substrates is a major compulsion for successful commercialization of this bioplastic, which is anticipated to reduce the cost of production as a result of advancing and intensifying research work. This review presents an insight and patent developments in the field of PHAs bioplastics.

Processing and Properties of Biopolymer/Polyhydroxyalkanoates Blends

In this paper, the processability and the performance of a biodegradable polymer, Mater-Bi, and of its blends with either a sample of poly (hydroxy alkanoates) (PHA) or with bacterial biomass containing PHAs were compared. Adding PHA or directly the biomass containing it allows improving the processability of the matrix. Moreover, the mechanical behaviour of the systems was compared considering two different preparation methods, namely compression and injection moulding. The injection moulded samples show poorer mechanical performances than those of the compression moulded systems. The impact strength significantly improves when PHA is added while it reduces when bacterial biomass is used instead. In this latter case this was likely due to the easier propagation of micro-cracks during the impact tests.

A thermostable #x003B2;-ketothiolase of polyhydroxyalkanoates (PHAs) in Thermus thermophilus: Purification and biochemical properties

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesised by numerous bacteria as intracellular carbon and energy storage compounds which accumulate as granules in the cytoplasm of the cells. The biosynthesis of PHAs, in the thermophilic bacterium T. thermophilus grown in a mineral medium supplemented with sodium gluconate as sole carbon source has been recently reported. Here, we report the purification at apparent homogeneity of a beta-ketoacyl-CoA thiolase from T. thermophilus, the first enzyme of the most common biosynthetic pathway for PHAs. B-Ketoacyl-CoA thiolase appeared as a single band of 45.5-kDa molecular mass on SDS/PAGE. The enzyme was purified 390-fold with 7% recovery. The native enzyme is a multimeric protein of a molecular mass of approximately of 182 kDa consisting of four identical subunits of 45.5 kDa, as identified by an in situ renaturation experiment on SDS-PAGE. The enzyme exhibited an optimal pH of approximately 8.0 and highest activity at 65 degrees C for both direction of the reaction. The thiolysis reaction showed a substrate inhibition at high concentrations; when one of the substrates (acetoacetyl CoA or CoA) is varied, while the concentrations of the second substrates (CoA or acetoacetyl CoA respectively) remain constant. The initial velocity kinetics showed a pattern of a family of parallel lines, which is in accordance with a ping-pong mechanism. beta-Ketothiolase had a relative low Km of 0.25 mM for acetyl-CoA and 11 microM and 25 microM for CoA and acetoacetyl-CoA, respectively. The enzyme was inhibited by treatment with 1 mM N-ethylmaleimide either in the presence or in the absence of 0.5 mM of acetyl-CoA suggesting that possibly a cysteine is located at/or near the active site of beta-ketothiolase.

Recent advances in microbial polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesised by numerous bacteria as an intracellular carbon and energy storage compound. These are accumulated in the cytoplasm of cells. A number of bacteria including Alcaligenes, Pseudomonas, recombinant Escherichia coli and methylotrophs have been used for the production of PHAs and high productivities have been achieved. Production of PHA by transgenic plants has been demonstrated on a laboratory-scale and large-scale production will be feasible in the near future. By controlling the monomer composition of PHA, it has been indicated that the physical properties of polymers can be regulated to a great extent. Even though PHAs have been recognised as a good candidate for biodegradable polymers, their high production cost limits their industrial application. It is hoped that with improvement in fermentation and downstream processing techniques, development of new recombinant strains and large-scale production by transgenic plants will reduce the cost of production of PHAs thereby making them competitive with conventional plastics.

Production of Hydroxyalkanoate Monomers by Microbial Fermentation

Hydroxyalkanoates (HA) can be widely used as chiral building blocks for the synthesis of fine chemicals. In this study, HA monomers were produced directly using genetic engineering techniques. The recombinant E. coli HB101 harboring β-ketothiolase (PhbA) and acetoacetyl-CoA reductase (PhbB) of Ralstonia eutropha was found to be able to produce more than 1 g L-' of 3HB monomer extracellularly after 48 h of fermentation. Heterogenous expression of (R)-3-hydroxydecanol-ACP: CoA transacylase gene (phaG) isolated from Pseudomonas putida in E. coli HB101 led to 587 mg L-' extracellular production of 3-hydroxydecanoic acid (3HD) from fructose. The results demonstrated that HA can be produced by recombinant organisms directly without going through the PHA hydrolyzation process.

Bacterial polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyalkanoates (HAs) synthesized by numerous bacteria as intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells. More than 80 HAs have been detected as constituents of PHAs, which allows these thermoplastic materials to have various mechanical properties resembling hard crystalline polymer or elastic rubber depending on the incorporated monomer units. Even though PHAs have been recognized as good candidates for biodegradable plastics, their high price compared with conventional plastics has limited their use in a wide range of applications. A number of bacteria including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, methylotrophs, pseudomonads, and recombinant Escherichia coli have been employed for the production of PHAs, and the productivity of greater than 2 g PHA/L/h has been achieved. Recent advances in understanding metabolism, molecular biology, and genetics of the PHA-synthesizing bacteria and cloning of more than 20 different PHA biosynthesis genes allowed construction of various recombinant strains that were able to synthesize polyesters having different monomer units and/or to accumulate much more polymers. Also, genetically engineered plants harboring the bacterial PHA biosynthesis genes are being developed for the economical production of PHAs. Improvements in fermentation/separation technology and the development of bacterial strains or plants that more efficiently synthesize PHAs will bring the costs down to make PHAs competitive with the conventional plastics.

Production of polyesters consisting of medium chain length 3-hydroxyalkanoic acids by Pseudomonas mendocina 0806 from various carbon sources.

Pseudomonas mendocina strain 0806 was isolated from oil-contaminated soil and found to produce polyesters consisting of medium chain length 3-hydroxyalkanoates (mclPHAs). The monomers of mclPHAs contained even numbers of carbon atoms, such as 3-hydroxyhexanoate (HHx or C6), 3-hydroxyoctanoate (HO or C8), and/or 3-hydroxydecanoate (HD or C10) as major components when grown on many carbon sources unrelated to their monomeric structures, such as glucose, citric acid, and carbon sources related to their monomeric structures, such as myristic acid, octanoate, or oleic acid. On the other hand, PHA containing both even and odd numbers of hydroxyalkanoates (HA) monomers was synthesized when the strain was grown on tridecanoic acid. The molar ratio of carbon to nitrogen (C/N) had a significant effect on PHA composition: the strain produced PHAs containing 97-99% of HD monomer when grown in a glucose ammonium sulfate medium of C/N<20, and 20% HO, and 80% of the HD monomer when growth was conducted in media containing C/N>40. It was demonstrated that the HO/HD ratio in the polymers remained constant in media with a constant C/N ratio, regardless of the glucose concentration. Up to 3.6 g/L cell dry weight containing 45% of PHAs was produced when the strain was grown for 48 h in a medium containing 20 g/L glucose with a C/N ratio of 40.

Starch alkanoates as models for thermoplastic polysaccharides

AbstractThe low degree of internal molecular mobility of stiff polysaccharide chains prevent any thermal transition in the temperature range of their chemical stability. Substituted starches were synthesised to find the structural range, i.e. the necessary amount and length of mobile side chains which support the molecule with high enough level of internal degrees of freedom. Esterification and transesterification with hydroxy alkanoates, their polymers and lactones were used. The reaction was best catalysed with strong delocalised bases. The thermal properties of these model substances were characterised.