Extraction Of Polyhydroxyalkanoates Research Articles

Extraction of polyhydroxyalkanoates from mixed microbial cultures: Impact on polymer quality and recovery

Polyhydroxyalkanoates (PHAs) can be extracted from mixed microbial cultures (MMCs) by means of dimethyl carbonate (DMC) or combination of DMC and sodium hypochlorite (NaClO). The protocol based on DMC, a green solvent never used before for the extraction of PHAs from MMC, allows an overall polymer recovery of 63%; also the purity and the molecular weight of the recovered polymers are good (98% and 1.2MDa, respectively). The use of NaClO pretreatment before DMC extraction increases the overall PHA recovery (82%) but lowers the mean molecular weight to 0.6–0.2MDa. A double extraction with DMC results to be the method of choice for the recovery of high quality PHAs from attractive but challenging MMCs.

METHODS OF EXTRACTION OF POLYHYDROXYALKANOATES FROM BACTERIAL BIOMASS

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters intracellularly accumulated by many bacteria as an energy reserve material and carbon source. These biopolymers may be extracted from cells after their production phase, and the extraction process involves various individual operations to ensure adequate removal of the biopolymer from the cells. During this process, the following aspects should be considered: reduction of product losses during different stages of the process to obtain a highly pure product, preservation of physical and thermal characteristics, and use of low toxicity chemicals to achieve sustainable production and avoid harming the environment. The impact of the costs of PHA extraction on the total cost of the production process may account for over 50% of the end-value of the product. Within this context, several methods of PHA extraction have been reported in the literature. These methods include the use of solvents, chemical digestion, enzymatic digestion, mechanical extraction with high-pressure homogenization and ultrasound, extraction using supercritical fluids, or a combination of these methods. The present review of the literature shows strategies for extraction processes of PHAs produced by bacteria involving cell destabilization and/or breakage, recovery, and purification of the biopolymer.

Start a Research on Biopolymer Polyhydroxyalkanoate (PHA): A Review

With the impending fossil fuel crisis, the search for and development of alternative chemical/material substitutes is pivotal in reducing mankind’s dependency on fossil resources. One of the potential substitute candidates is polyhydroxyalkanoate (PHA). PHA is a carbon-neutral and valuable polymer that could be produced from many renewable carbon sources by microorganisms, making it a sustainable and environmental-friendly material. At present, PHA is not cost competitive compared to fossil-derived products. Encouraging and intensifying research work on PHA is anticipated to enhance its economic viability in the future. The development of various biomolecular and chemical techniques for PHA analysis has led to the identification of many PHA-producing microbial strains, some of which are deposited in culture collections. Research work on PHA could be rapidly initiated with these ready-to-use techniques and microbial strains. This review aims to facilitate the start-up of PHA research by providing a summary of commercially available PHA-accumulating microbial cultures, PHA biosynthetic pathways, and methods for PHA detection, extraction and analysis.

Screening, Optimization and Extraction of Polyhydroxyalkanoates (PHAs) from Bacillus thuringienesis

Aims: This study illustrated obtaining bacterial isolates capable to produce polyhydroxyalkanoates (PHA) under stressed conditions and also using cheap wastes for production process. Study Design: Two­step throughput screening of 50 bacterial isolates by lipophylic stain (Sudan black B) and flouroscence stain (Nile red) will be carried on, then the best condition for PHA production followed by identification of most potent isolate by molecular charterization will be investigated. Place and Duration of Study: The study were performed in physiological lab in botany & microbiology department in faculty of science, Al­azhar university and NRC from October 2012 until April 2014. Methodology: Bacterial isolates will be investigated using two different indicator stains, Sudan Black and Nile Red, for PHA productivity then the highly producing isolate will be identified. Factors controlling PHA production and stressed condition will be studied Original Research Article Desouky et al.; JABB, Article no. JABB.2014.004 41 alternatively depends on increasing of PHA production which will be assayed quantitatively by converting PHA to crotonic acid. Biopolymer will be extracted using successive solvents. Result: Five soil samples were collected from different localities contaminated with industrial wastes and 50 isolates of bacteria were purified then screened for PHA production by using Sudan black B as a primary screening and confirmed by fluorescent Nile red staining. Eleven promising bacterial isolates were selected based on their PHA yields. Out of eleven natural promising isolates, BS11 was found to be the most efficient PHA producer and identified as Bacillus thuringiensis (KJ206079). The effect of different conditions on PHA produced by B. thuringiensis including carbon sources, nitrogen sources, incubation temperatures, pH and incubation periods were studied. The highest amount of PHA was obtained from this isolate using medium containing 30 g/l molasses, 0.8 g/L ammonium sulphate at pH 7.5 and incubation temp at 35oC and after 72 hours. In conclusion, after the optimization of PHA synthesizing conditions, B. thuringiensis accumulate up to 69 % of its dry weight and can be employed for industrial production. Conclusion: The experiment indicate the efficiency of two­throughput screening systems targeting PHA producing isolates. Also optmiziation of PHA producing factors for the most potent producing strain, Bacillus thuringiensis (KJ206079), was increased from 2.5 g/L to 4.1 g/L and represent about 69% cell dry weight.

Improved detergent-based recovery of polyhydroxyalkanoates (PHAs)

Extracting polyhydroxyalkanoate (PHA) polymer from bacterial cells often involves harsh conditions, including use of environmentally harmful solvents. We evaluated different detergents under various conditions to extract PHA from Ralstonia eutropha and Escherichia coli cells. Most detergents tested recovered highly pure PHA polymer from cells in amounts that depended on the percentage of polymer present in the cell. Detergents such as linear alkylbenzene sulfonic acid (LAS-99) produced a high yield of high purity polymer, and less detergent was needed compared to the amount of SDS to produce comparable yields. LAS-99 also has the advantage of being biodegradable and environmentally safe. Chemical extraction of PHA with detergents could potentially minimize or eliminate the need to use harsh organic solvents, thus making industrial PHA production a cleaner technology process.

PHA bioplastic: A value‐added coproduct for biomass biorefineries

AbstractThe petroleum industry has optimized profits by producing value‐added coproducts, such as plastics and chemicals, in addition to primary liquid fuels. A similar coproduct strategy applied to biorefineries processing cellulosic biomass to liquid fuels and/or energy would transform a technology that is marginally economic, depending on oil prices, to a sustainable business with enhanced revenue streams from multiple coproducts. The challenge is finding a biobased coproduct that is compatible with a biorefinery scenario and where markets warrant its production on a similar scale as liquid fuels and/or energy. Polyhydroxyalkanoate (PHA) bioplastics represent a coproduct that would be entirely compatible with either production of liquid fuels by hydrolyzing the residual biomass after PHA extraction or by alternative thermochemical processes. PHA bioplastics possess properties making them suitable replacements for many of the applications currently served by petroleum‐based plastics, thus providing tremendous market potential. Proof‐of‐concept technology for production of these plastics in several crops of agronomic interest has been demonstrated. In this review, we show that the potential for developing biomass‐based biorefineries producing liquid fuels and a value‐added coproduct is both real and realizable. Examples using switchgrass producing PHA bioplastics as a coproduct are described. © 2009 Society of Chemical Industry and John Wiley & Sons, Ltd.

Screening of different contaminated environments for polyhydroxyalkanoates-producing bacterial strains

Total sixteen bacterial strains were isolated and purified from the samples collected from sugarcane molasses soil, sewage water and long-chain-hydrocarbon-contaminated area of the Punjab University, Lahore, Pakistan. Tolerance to different antibiotics was studied and strains showed multiple antibiotic resistance. All strains were characterized for Gram stain, biochemical reactions and polyhydroxyalkanoate (PHA) production. Total fourteen strains were Gram negative and two were Gram positive, while biochemically nine PHA producers showed affiliation to Pseudomonas, Enterobacter, Citrobacter, Bacillus and Escherichia. Screening for PHA production was done by Sudan black staining and nine out of sixteen strains exhibited PHA producing ability. PHA production was optimized for different growth parameters, like nitrogen concentration, pH and temperature. PHA extraction was done by solvent extraction method. Bacterial strains US1 and M1 accumulated up to 30% PHA of their cell dry weight on PHA extraction by solvent extraction method. Bacterial strain US1 was identified by 16S rRNA gene analysis as P. aeruginosa (DQ455691). PHA production was confirmed by PCR amplification of 500 bp fragment from PHA polymerase (Pha C) gene; five strains from nine PHA producers gave positive results on PCR. Pha C gene fragment of US1 was sequenced and submitted to Gene Bank under the accession number DQ455690. The amino acid sequence showed homology using the protein BLAST at 129–132 sites with different PHA synthases of the Pseudomonas sp.

Analysis of bacterial strains from contaminated and non-contaminated sites for the production of biopolymers

A total 18 strains were collected from non-contaminated and contaminated environments, and were purified. All purified strains were characterized for Gram reaction and biochemical analysis. Screening for bioplastic production was done by Sudan black staining. Strains isolated from non-contaminated sites showed no polyhydroxyalkanoate (PHA) production. Biochemical analysis showed that PHA producing strains belong to Pseudomonas, Citrobacter, Enterobacter, Klebsiella, Escherichia and Bacillus genera. PHA extraction was done by sodium hypochlorite digestion method. Strain MS2D showed maximum percentage (65%). Production of PHA was optimized for different temperatures and pH. Selected strains were also tested for exopolysaccharides (EPS) production on EPS detection medium by solvent precipitation method. Four out of nine strains exhibited EPS production ability. EPS production was also optimized for different temperatures and pH.

Analysis of bacterial strains from contaminated and non-contaminated sites for the production of biopolymers

A total 18 strains were collected from non-contaminated and contaminated environments, and were purified. All purified strains were characterized for Gram reaction and biochemical analysis. Screening for bioplastic production was done by Sudan black staining. Strains isolated from non-contaminated sites showed no polyhydroxyalkanoate (PHA) production. Biochemical analysis showed that PHA producing strains belong to Pseudomonas, Citrobacter, Enterobacter, Klebsiella, Escherichia and Bacillus genera. PHA extraction was done by sodium hypochlorite digestion method. Strain MS2D showed maximum percentage (65%). Production of PHA was optimized for different temperatures and pH. Selected strains were also tested for exopolysaccharides (EPS) production on EPS detection medium by solvent precipitation method. Four out of nine strains exhibited EPS production ability. EPS production was also optimized for different temperatures and pH.