Polyhydroxyalkanoic Acid Research Articles

Porous red mud ceramsite for aquatic phosphorus removal: Application in constructed wetlands

Red mud (RM) and spent oyster mushroom substrate (SOMS), by-products of industrial and agricultural production, can be recycled for polluted freshwater purification, bringing about a win-win situation. In this study, unacidified RM and RM acidified with oxalic acid (O-RM) and hydrochloric acid (H-RM), respectively, were mixed with SOMS to produce a porous ceramsite as a potential constructed wetlands (CWs) substrate. The results showed that the O-RM, H-RM, and RM ceramsites displayed fine compressive strengths of 7.75 ± 1.14, 8.40 ± 1.30, and 8.84 ± 0.69 MPa after calcining at 950 °C for 30 min, respectively. The phosphorus adsorption capacities of H-RM, O-RM, and RM ceramsite at a solid-liquid ratio of 25 g/L were 1.18 mg/g, 0.88 mg/g, and 1.06 mg/g, respectively. Toxicity release experiments showed that the ceramsites did not cause secondary environmental pollution, except for arsenic (ranging from 0.210 to 0.238 mg/L). The H-RM ceramsite was tested in a tidal flow-vertical flow CW (TF-VFCW) with Iris pseudacorus L. and Canna indica L plants. In the TF-VFCW, the average chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) removal rates were 81.01, 90.25, 66.90, and 77.32 %, respectively. Plant growth had less impact on COD and NH4-N removal but had greater limited TN and TP removal. Scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis confirmed that acid pretreatment and the incorporation of SOMS significantly increased the surface and interior porous structures of the ceramsite and enhanced phosphate adsorption by the polyhydroxyl aluminum-iron complex ions. Bacteroides and Campylobacter used the energy produced during polyhydroxyalkanoic acid (PHA) catabolism to absorb phosphorus. Therefore, the synergistic effect of the substrate, plants, and microorganisms achieved the removal of phosphorus from CWs and offered effective and environmentally friendly recycling of RM and SOMS.

Using runaway replication to express polyhydroxyalkanoic acid (pha) genes from a novel marine bacterium in enteric bacteria: The influence of temperature and phasins on PHA accumulation.

While plastics have revolutionized our world, plastic waste has serious environmental and economic impacts. Polyhydroxyalkanoic acid (PHA) is a bacterial carbon and energy reserve shown to be both biodegradable and biocompatible and could potentially replace conventional plastics. However, cost-effective mass production remains elusive. Bacteria often accumulate PHA as cytoplasmic granules. PHA synthase creates the PHA polymer from acetoacyl-CoA monomers, while phasins are small multifunctional proteins that are found in abundance on the granule surface. The PHA synthase gene from a novel marine isolate, Vibrio B-18 (or B-18), was placed in the presence or absence of an upstream phasin gene in a runaway replication plasmid using polymerase chain reaction (PCR) technology. Plasmid gene expression may be induced chemically or thermally. Overexpression of the PHA genes was demonstrated by SDS-PAGE analysis, and microscopy was used to detect PHA accumulation in three different enteric bacteria (Escherichia coli, Klebsiella aerogenes, and Shigella flexneri). While the B-18 genes were clearly overexpressed at 41°C, PHA accumulation occurred more readily at the lower (30°C) non-inducing temperature regardless of chemical induction if the phasin gene was present. A mutational analysis confirmed the identity of the start codon for the PHA synthase gene and provided evidence supporting the requirement for phasins to allow for PHA accumulation in the recombinant hosts. The findings described in this study confirm the conclusions obtained from related studies from other laboratories and lend support to the importance of including a phasin gene in addition to the basic genes needed for PHA synthesis and accumulation in recombinant enteric bacteria, such as Escherichia coli, Klebsiella aerogenes, and Shigella flexneri.

Winogradskyella luteola sp.nov., Erythrobacter ani sp. nov., and Erythrobacter crassostrea sp.nov., isolated from the hemolymph of the Pacific Oyster Crassostrea gigas

Three new bacterial strains, WHY3T, WH131T, and WH158T, were isolated and described from the hemolymph of the Pacific oyster Crassostrea gigas utilizing polyphasic taxonomic techniques. The 16S rRNA gene sequence analysis revealed that strain WHY3T was a member of the genus Winogradskyella, whereas strains WHI31T and WH158T were members of the genus Erythrobacter. According to the polygenomic study the three strains formed individual lineages with strong bootstrap support. The comparison of dDDH-and ANI values, percentage of conserved proteins (POCP), and average amino acid identity (AAl) between the three strains and their relatives established that the three strains represented two separate genera. Menaquinone-6 was reported as the major respiratory quinone in strain WHY3T and Ubiquinone-10 for strains WH131T and WH158T, respectively. The major cellular fatty acids for strain WHY3T were C15:0, anteiso-C15:1 ω7c, iso-C15:0, C16:1ω7c. The major cellular fatty acids for strains WH131T and WH158T were C14:02-OH and t18:1ω12 for WH131T and C17:0, and C18:1ω7c for strain WH158T. Positive Sudan Black B staining Indicated the presence of polyhydroxyalkanoic acid granules for strains WH131T and WH158T but not for strain WHY3T. The DNA G + C contents of strains WHY3T, WH131T and WH158T were 34.4, 59.7 and 56.6%, respectively. Gene clusters predicted some important genes involved in the bioremediation process. Due to the accomplishment of polyphasic taxonomy, we propose three novel species Winogradskyella luteola sp.nov. (type strain WHY3T = DSM 111804T = NCCB 100833T), Erythrobacter ani sp.nov. (WH131T = DSM 112099T = NCCB 100824T) and Erythrobacter crassostrea sp.nov. (WH158T = DSM 112102T = NCCB 100877T).

Co-upgrading of ethanol-assisted depolymerized lignin: A new biological lignin valorization approach for the production of protocatechuic acid and polyhydroxyalkanoic acid

This study presents a promising biological co-upgrading of ethanol-assisted depolymerized lignin (EDL) into protocatechuic acid (PCA) and polyhydroxyalkanoic acid (PHA) without any separation process. A depolymerized alkali lignin containing various G-lignin-type monomers at a concentration of 77 mg/mL was used for co-upgrading. An engineered Pseudomonas putida KT2440 strain was constructed by knocking out the protocatechuate 3, 4-dioxygenase, expression of the formaldehyde utilization pathway, and the expression of aldehyde dehydrogenase to enhance the efficiency of the ethanol utilization pathway. The growth and production of value-added bioproducts have been promoted by the utilization of formaldehyde, resulted in 6.73 ± 0.26 mg/L of PCA with a 17.5% (w/w) yield of total lignin monomers, and 303.66 ± 26.75 mg/L of PHA with 21.26% (w/w) of dry cell weight from 0.5 mL EDL. Moreover, the ethanol solvent used for lignin depolymerization was also utilized along with depolymerized lignin for co-upgrading to value-added products.

Nitrate removal from low C/N wastewater at low temperature by immobilized Pseudomonas sp. Y39-6 with versatile nitrate metabolism pathways

For solving the challenge in nitrate removal from low C/N wastewater at low temperature, Pseudomonas sp. Y39-6 was isolated and used in nitrate removal. It showed aerobic-heterotrophic denitrification with rate of 1.77 ± 0.31 mg/L·h and unusual aerobic-autotrophic nitrate removal (rate of 0.324 mg/L·h). The aerobic-autotrophic nitrate removal mechanisms were deep investigated by analyzing the nitrate removal process and genomic information. At aerobic-autotrophic condition, the strain Y39-6 could assimilate nitrate to amino acid (NO3− + PHA + CO2 → C5H7O2N) with the carbon source from Polyhydroxyalkanoic acid (PHA) degradation and CO2 fixation. Flagella motivation, swarming activity and extracellular polymeric substances (EPS) production regulated Pseudomonas sp. Y39-6 forming biofilm. Carriers immobilized with Pseudomonas sp. Y39-6 were used in moving bed biofilm reactor (MBBR) and achieved 24.83% nitrate removal at C/N < 1 and 4 °C. Results of this study provided a practical way for nitrogen removal from low C/N wastewater in cold region.

Engineering the Yeast Yarrowia lipolytica for Production of Polylactic Acid Homopolymer.

Polylactic acid is a plastic polymer widely used in different applications from printing filaments for 3D printer to mulching films in agriculture, packaging materials, etc. Here, we report the production of poly-D-lactic acid (PDLA) in an engineered yeast strain of Yarrowia lipolytica. Firstly, the pathway for lactic acid consumption in this yeast was identified and interrupted. Then, the heterologous pathway for PDLA production, which contains a propionyl-CoA transferase (PCT) converting lactic acid into lactyl-CoA, and an evolved polyhydroxyalkanoic acid (PHA) synthase polymerizing lactyl-CoA, was introduced into the engineered strain. Among the different PCT proteins that were expressed in Y. lipolytica, the Clostridium propionicum PCT exhibited the highest efficiency in conversion of D-lactic acid to D-lactyl-CoA. We further evaluated the lactyl-CoA and PDLA productions by expressing this PCT and a variant of Pseudomonas aeruginosa PHA synthase at different subcellular localizations. The best PDLA production was obtained by expressing the PCT in the cytosol and the variant of PHA synthase in peroxisome. PDLA homopolymer accumulation in the cell reached 26 mg/g-DCW, and the molecular weights of the polymer (Mw = 50.5 × 103 g/mol and Mn = 12.5 × 103 g/mol) were among the highest reported for an in vivo production.

Asymmetric Open-Closed Dimer Mechanism of Polyhydroxyalkanoate Synthase PhaC.

SummaryBiodegradable polyester polyhydroxyalkanoate (PHA) is a promising bioplastic material for industrial use as a replacement for petroleum-based plastics. PHA synthase PhaC forms an active dimer to polymerize acyl moieties from the substrate acyl-coenzyme A (CoA) into PHA polymers. Here we present the crystal structure of the catalytic domain of PhaC from Chromobacterium sp. USM2, bound to CoA. The structure reveals an asymmetric dimer, in which one protomer adopts an open conformation bound to CoA, whereas the other adopts a closed conformation in a CoA-free form. The open conformation is stabilized by the asymmetric dimerization and enables PhaC to accommodate CoA and also to create the product egress path. The bound CoA molecule has its β-mercaptoethanolamine moiety extended into the active site with the terminal SH group close to active center Cys291, enabling formation of the reaction intermediate by acylation of Cys291.

Preparation of novel mcl-PHA by green synthesis: influence of active small molecule via esterification effect on side chain

Microbial production of polyhydroxyalkanoic acid (PHA) with customized features has been attempted by humans through metabolic engineering. However, few studies have explored the green chemical synthesis of customized PHA using hydroxy fatty acids. In the present study, new mcl-PHA having C16-co-C16, blocked by esterification of hydroxy groups in the side chain, was synthesized by melt polycondensation using aleuritic acid (9, 10, 16-trihydroxyhexadecanoic acid) and lactic acid as long-chain fatty acid monomers and active blocking molecule, respectively. The results showed that when the two monomers reacted at 150 °C for 24 h, the properties of PHA were largely retained, along with free hydroxyl groups as much as possible. Comparison of the effect of different ratios of active small molecule (lactic acid) on the properties of new mcl-PHA revealed that copolymerization mainly happened between the long-chain monomers, and lactic acid served as a blocker by esterification in the side chain on the hydroxy groups of mcl-PHA. Further, the properties of side chain-esterified mcl-PHA (SCE-mcl-PHA) changed from rigid to soft with increasing ratio of active lactic acid monomer. The tensile strength of mcl-PHA was similar to that of commercially available products PLA and PHBV. The mechanical properties of SCE-mcl-PHA significantly changed by adding only 5 wt% lactic acid monomer. Besides, the cell proliferation analysis showed that the new PHA had minimum cytotoxicity, which was close to PLA and PHBV. Therefore, these new mcl-PHA and SCE-mcl-PHA have great potential for application in food, medicine, cosmetics, and other fields, and hence require further investigation.

Co-production of fully renewable medium chain α-olefins and bio-oil via hydrothermal liquefaction of biomass containing polyhydroxyalkanoic acid.

Medium chain-length linear α-olefins (mcl-LAO) are versatile precursors to commodity products such as synthetic lubricants and biodegradable detergents, and have been traditionally produced from ethylene oligomerization and Fischer–Tropsch synthesis. Medium chain-length polyhydroxyalkanoic acid (mcl-PHA) can be produced by some microorganisms as an energy storage. In this study, Pseudomonas putida biomass that contained mcl-PHA was used in HTL at 300 °C for 30 min, and up to 65 mol% of mcl-PHA was converted into mcl-LAO. The yield and quality of the bio-oil co-produced in the HTL was remarkably improved with the biomass rich in mcl-PHA. Experiments with extracted mcl-PHA revealed the degradation mechanism of mcl-PHA in HTL. Overall, this work demonstrates a novel process to co-produce mcl-LAO and bio-oil from renewable biomass.

Production and characterization of polyhydroxyalkanoic acid from Bacillus thuringiensis using different carbon substrates

Polyhydroxyalkanoic acids (PHA) are biodegradable microbially synthesised polymers which can act as alternatives to conventional petrochemical based plastics. Bacterial isolates from soil and sewage samples were screened for the ability to accumulate PHA using Sudan Black B dye, and growth conditions of the best PHA accumulating bacterium was optimized. The PHA produced was characterized by FTIR spectroscopy. Eight PHA-producing bacteria were isolated and isolate SBC4 which had the highest percentage accumulation of 30% was genotypically identified as Bacillus thuringiensis and selected for further studies. Glucose and ammonium sulfate supplementation afforded the optimum cultural conditions for cell growth and PHA accumulation yielding 0.33g/l and 0.40g/l respectively. B. thuringiensis SBC4 utilized corn bran, corn cob and wheat bran for PHA production, with corn cob yielding the highest PHA content of 21.05%. The optimum pH, temperature and incubation time for PHA productions were 7.0, 37°C and 48h. The use of all the optimum conditions in a newly modified medium increased the PHA content, with an overall increase in PHA accumulation from 30% to 44.96% equivalent to an increase of 50% in PHA yield. The presence of major peaks such as CO stretching, CH vibrations, COC stretching confirmed PHA production.

Mesorhizobium bacterial strains isolated from the legume Lotus corniculatus are an alternative source for the production of polyhydroxyalkanoates (PHAs) to obtain bioplastics.

Polyhydroxyalkanoic acids (PHAs) are natural polyesters that can be used to produce bioplastics which are biodegradable. Numerous microorganisms accumulate PHAs as energy reserves. Combinations of different PHAs monomers lead to the production of bioplastics with very different properties. In the present work, we show the capability of strains belonging to various phylogenetic lineages within the genus Mesorhizobium, isolated from Lotus corniculatus nodules, to produce different PHA monomers. Among our strains, we found the production of 3-hydroxybutyrate, 3-hydroxyvalerate, 3-hydroxydodecanoate, and 3-hydroxyhexadecanoate. Most of the PHA-positive strains were phylogenetically related to the species M. jarvisii. However, our findings suggest that the ability to produce different monomers forming PHAs is strain-dependent.

Amorphous poly(3‐hydroxybutyrate) nanoparticles prepared with recombinant phasins and PHB depolymerase

ABSTRACTPhasin protein (PhaP) is known to anchor into the matrix of phospholipid surrounding polyhydroxyalkanoic acid (PHA) inclusion bodies formed in bacterial cells and regulate the size of the granules, as well as the number of PHA granules. To investigate the effect of phasin on the formation of artificial poly(3‐hydroxybutyrate) (P(3HB)) granules in vitro, (His)6‐tagged or GST‐fusion recombinant phasin was prepared and utilized for the artificial granule preparation. In addition, a P(3HB) depolymerase was coloaded with the recombinant phasin to prepare self‐degradable phasin‐coated P(3HB) granules. A water/chloroform two‐phase emulsion technique was used, in which the emulsification was carried out by sonication, and the chloroform in the emulsion was removed by stirring‐aided evaporation at room temperature or 65°C. Slower chloroform removal at room temperature produced better spherically shaped P(3HB) nanogranules, which were uniformly sized (∼100 to 200 nm in diameter). The self‐degradability of P(3HB) depolymerase‐loaded P(3HB) nanogranules was investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41074.

Production of (R)-3-hydroxybutyric acid by Burkholderia cepacia from wood extract hydrolysates.

(R)-hydroxyalkanoic acids (R-HAs) are valuable building blocks for the synthesis of fine chemicals and biopolymers because of the chiral center and the two active functional groups. Hydroxyalkanoic acids fermentation can revolutionize the polyhydroxyalkanoic acids (PHA) production by increasing efficiency and enhancing product utility. Modifying the fermentation conditions that promotes the in vivo depolymerization and secretion to fermentation broth in wild type bacteria is a novel and promising approach to produce R-HAs. Wood extract hydrolysate (WEH) was found to be a suitable substrate for R-3-hydroxybutyric acid (R-3-HB) production by Burkholderia cepacia. Using Paulownia elongate WEH as a feedstock, the R-3-HB concentration in fermentation broth reached as high as 14.2 g/L after 3 days of batch fermentation and the highest concentration of 16.8 g/L was obtained at day 9. Further investigation indicated that the composition of culture medium contributed to the enhanced R-3-HB production.

Rhamnolipids Obtained from a PHA‐Negative Mutant of Pseudomonas aeruginosa 47T2 ΔAD: Composition and Emulsifying Behavior

AbstractPseudomonas aeruginosa 47T2 (NCBIM 40044) synthesizes polyhydroxyalkanoic acids (PHAs) and rhamnolipids (Rhls). The knockout mutant for PHAs biosynthesis, P. aeruginosa 47T2 ΔAD prepared in this study, increased the cellular yield of Rhls production by 28 %. The Rhls mixture (composed up to eight homologs) reduced the water surface tension to 31.67 mN/m with a critical micelle concentration of 105 mg/L. The IC50 (μg/mL) of the neutral red uptake assay and methylthiazol tetrazolium assay ranged between 53.9 and 72 μg/mL, which is similar to that of sodium dodecyl sulfate (SDS). Rhamnolipids had a lower hemolytic effect at 110.8 μg/ml than SDS, a commercial anionic surfactant, at 43.6 μg/mL. This suggests that the Rhls mixture could be used in topical pharmaceutical and cosmetic applications or cleansers as a biosurfactant. The emulsifying properties in water/oil dispersions were determined using ternary phase diagrams at 25 °C. Isopropyl myristate, soybean oil, olive oil and Casablanca oil were used as the oil components. Total emulsions were obtained with most of the oils.

Simultaneous Inhibition of Rhamnolipid and Polyhydroxyalkanoic Acid Synthesis and Biofilm Formation in Pseudomonas aeruginosa by 2-Bromoalkanoic Acids: Effect of Inhibitor Alkyl-Chain-Length

Pseudomonas aeruginosa, an opportunistic human pathogen is known to synthesize rhamnolipid and polyhydroxyalkanoic acid (PHA) of which the acyl-group precursors (e.g., (R)-3-hydroxydecanoic acid) are provided through RhlA and PhaG enzyme, respectively, which have 57% gene sequence homology. The inhibitory effect of three 2-bromo-fatty acids of 2-bromohexanoic acid (2-BrHA), 2-bromooctanoic acid (2-BrOA) and 2-bromodecanoic acid (2-BrDA) was compared to get an insight into the biochemical nature of their probable dual inhibition against the two enzymes. The 2-bromo-compounds were found to inhibit rhamnolipid and PHA synthesis simultaneously in alkyl-chain-length dependent manner at several millimolar concentrations. The separate and dual inhibition of the RhlA and PhaG pathway by the 2-bromo-compounds in the wild-type cells was verified by investigating their inhibitory effects on the rhamnolipid and PHA synthesis in P. aeruginosa ΔphaG and ΔrhlA mutants. Unexpectedly, the order of inhibition strength was found 2-BrHA (≥90% at 2 mM) > 2-BrOA > 2-BrDA, equally for all of the rhamnolipids and PHA synthesis, swarming motility and biofilm formation. We suggest that the novel strongest inhibitor 2-BrHA could be potentially exploited to control the rhamnolipid-associated group behaviors of this pathogen as well as for its utilization as a lead compound in screening for antimicrobial agents based on new antimicrobial targets.

Polyhydroxyalkanoic acids from structurally-unrelated carbon sources in Escherichia coli

Polyhydroxyalkanoates (PHAs) that contain varied monomers with different chain lengths/structures were normally synthesized when a structurally-related precursor was present. The biosynthesis of PHAs from unrelated carbon sources in microorganisms including Escherichia coli met many challenges in the past. Recently, with the development of metabolic engineering and synthetic biology, the production of PHAs from unrelated carbon sources obtained a breakthrough. Polyesters containing 2-hydroxypropionate, 3-hydroxypropionate, 4-hydroxybutyrate, 3-hydroxyvalarate, and medium-chain-length 3-hydroxyalkanoate monomers can all be synthesized in E. coli by integrating exogenous or endogenous pathways and/or genes. This review will summarize the progresses in this area. In addition, the strategies that lead to the production of PHAs with varied monomers and high polymer content in the cell are discussed.

Hydroxy-fatty acid production in a Pseudomonas aeruginosa 42A2 PHA synthase mutant generated by directed mutagenesis

Pseudomonas aeruginosa 42A2 growing on waste frying oils is capable to synthesize polyhydroxyalkanoic acids (PHAs) and hydroxy-fatty acids as a result of several enzymatic conversions. In order to study the physiological role of PHA biosynthesis in P. aeruginosa with respect to the synthesis of hydroxy-fatty acids, an unmarked deletion mutant deficient for PHA biosynthesis was generated in P. aeruginosa 42A2. A combination of the sacB-based negative selection system with a cre-lox antibiotic marker recycling method was used for mutant isolation. Electron microscopy, nuclear magnetic resonance analysis, and transmission electron microscopy confirmed that PHA accumulation was completely abolished in the mutant strain. Interestingly, the new mutant strain showed higher carbon and oxygen uptake rate than the wild-type strain and higher efficiency in the conversion of oleic acid into (E)-10-hydroxy-8-octadecenic acid-octadecenoic acid.

Metabolic relationship between polyhydroxyalkanoic acid and rhamnolipid synthesis in Pseudomonas aeruginosa: Comparative 13C NMR analysis of the products in wild-type and mutants

Polyhydroxyalkanoic acids (PHAs) and rhamnolipids considered as biotechnologically important compounds are simultaneously produced by Pseudomonas aeruginosa. Both are synthesized from common precursors, ( R)-3-hydroxyfatty acids. To find the probable metabolic relationship between their syntheses, we investigated the PHA and rhamnolipids production in four pha ( phaC1, phaC2, phaZ, and phaG), four rhl ( rhlA, rhlB, rhlR, and rhlI) and rpoS mutant strains of P. aeruginosa PA14 and PAO1 grown in minimal medium containing 70 mM fructose or 30 mM decanoic acid. Higher PHA accumulation was found in the rhamnolipid-negative mutants than in the wild-type strains, suggesting that 3-hydroxyfatty acid precursors become more available for PHA synthesis when rhamnolipids synthesis is absent. However, compared to the wild-type strains, rhamnolipids production was not enhanced in the four pha mutants of P. aeruginosa PA14 and PAO1 which indicates that rhamnolipids production in P. aeruginosa could be tightly regulated at the transcriptional level by a quorum-sensing response. The metabolic pathways for PHA and rhamnolipid synthesis from medium-chain-length fatty acids were also investigated using octanoic- 1- 13 C acid. 13C NMR analysis revealed that the monomer-unit ( R)-3-hydroxyoctanoate- 1- 13 C being converted from the octanoic acid substrate was effectively incorporated into PHA. In the rhamnolipid synthesis, the ( R)-3-hydroxyoctanoate- 1- 13 C is suggested to be firstly converted to ( R)-3-hydroxydecanoate- 1, 3- 13 C via fatty acid de novo biosynthesis pathway and then further processed into ( R)-3-(( R)-3-hydroxyalkanoyloxy)alkanoic acids (HAAs) via RhlA. The ratio of mono- to dirhamnolipids in the product depended on the type of carbon sources. The rhlB mutant could be exploited as an efficient producer of the important biosurfactant HAAs (e.g., ∼700 mg/L HAAs was obtained when grown on 60 mM octanoic acid).

Evaluation of bacterial strains isolated from oil-contaminated soil for production of polyhydroxyalkanoic acids (PHA)

Abstract Samples of eight geographically distinct soils contaminated with crude oil were screened for polyhydroxyalkanoic acid (PHA) producing bacterial strains. Twenty three bacterial strains were able to accumulate PHA when sodium gluconate or sodium octanoate was used as the sole carbon source. Biochemical tests and 16S rRNA sequencing identified bacteria of the genera Pseudomonas, Acinetobacter, Sphingobacterium, Brochothrix, Caulobacter, Ralstonia, Burkholderia and Yokenella. Three of the bacterial strains have never been reported to produce PHA. The phylogenetic analysis of the PHA synthase (phaC) gene of these bacteria showed a close homology with the phaC gene of different Pseudomonas species. This study indicates that stressed environments like oil-contaminated sites can be potential sources of medium-chain-length PHA producers.

Perspectives to produce positively or negatively charged polyhydroxyalkanoic acids

An overview is provided on the possibilities of producing positively and negatively charged poly(β-hydroxyalkanoates), PHAs. A large variety of bacterial polyesters with functionalized terminal side chains can be produced in microbial fermentation processes by a direct polymerization of respective carbon sources, that is, carbon sources that carry functional groups in their ω-position. However, charged PHAs are not accessible by a direct approach and must be synthesized via polymer-analogous reactions of functionalized bacterial polyesters. PHA polyanions are produced by converting the terminal functional groups into carboxylate groups, while PHA polycations are produced by introducing terminal amino groups. PHAs with terminal vinyl groups emerged as most suitable PHA precursors, as they can be produced in relatively high yields and the double bonds are sufficiently reactive. The oxidation of vinyl groups yields PHA polyanions. The conversion of terminal vinyl groups into epoxides with a subsequent ring-opening reaction with an amine yields PHA polycations. Other functionalized PHA that potentially lend themselves to polymer-analogous reactions are reviewed.