Large-scale production of poly(3-hydroxyvaleric acid) by fermentation ofChromobacterium violaceum, processing, and characterization of the homopolyester

Quantification of the Monomer Compositions of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and Poly(3-hydroxyvalerate) by Alkaline Hydrolysis and Using High-Performance Liquid Chromatography

With the growing interest in bioplastics, there is an urgent need to develop rapid analysis methods linked to production technology development. This study focused on the production of a commercially non-available homopolymer, poly(3-hydroxyvalerate) (P(3HV)), and a commercially available copolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)), through fermentation using two different bacterial strains. The bacteria Chromobacterium violaceum and Bacillus sp. CYR1 were used to produce P(3HV) and P(3HB-co-3HV), respectively. The bacterium Bacillus sp. CYR1 produced 415 mg/L of P(3HB-co-3HV) when incubated with acetic acid and valeric acid as the carbon sources, whereas the bacterium C. violaceum produced 0.198 g of P(3HV)/g dry biomass when incubated with sodium valerate as the carbon source. Additionally, we developed a fast, simple, and inexpensive method to quantify P(3HV) and P(3HB-co-3HV) using high-performance liquid chromatography (HPLC). As the alkaline decomposition of P(3HB-co-3HV) releases 2-butenoic acid (2BE) and 2-pentenoic acid (2PE), we were able to determine the concentration using HPLC. Moreover, calibration curves were prepared using standard 2BE and 2PE, along with sample 2BE and 2PE produced by the alkaline decomposition of poly(3-hydroxybutyrate) and P(3HV), respectively. Finally, the HPLC results obtained by our new method were compared using gas chromatography (GC) analysis.

Polyhydroxyalkanoates (PHAs): Biopolymers for Biofuel and Biorefineries

Fossil fuels are energy recourses that fulfill most of the world's energy requirements. However, their production and use cause severe health and environmental problems including global warming and pollution. Consequently, plant and animal-based fuels (also termed as biofuels), such as biogas, biodiesel, and many others, have been introduced as alternatives to fossil fuels. Despite the advantages of biofuels, such as being renewable, environmentally friendly, easy to source, and reducing the dependency on foreign oil, there are several drawbacks of using biofuels including high cost, and other factors discussed in the fuel vs. food debate. Therefore, it is imperative to produce novel biofuels while also developing suitable manufacturing processes that ease the aforementioned problems. Polyhydroxyalkanoates (PHAs) are structurally diverse microbial polyesters synthesized by numerous bacteria. Moreover, this structural diversity allows PHAs to readily undergo methyl esterification and to be used as biofuels, which further extends the application value of PHAs. PHA-based biofuels are similar to biodiesel except for having a high oxygen content and no nitrogen or sulfur. In this article, we review the microbial production of PHAs, biofuel production from PHAs, parameters affecting the production of fuel from PHAs, and PHAs biorefineries. In addition, future work on the production of biofuels from PHAs is also discussed.

Metabolic engineering of Pseudomonas putida for the production of various types of short-chain-length polyhydroxyalkanoates from levulinic acid

Poly(3-hydroxybutyrate), a short-chain-length polyhydroxyalkanoate (scl-PHA), is considered as a good alternative to conventional synthetic plastics. However, various biopolymers with diverse characteristics are still in demand. In this study, four different types of scl-PHA were successfully produced by engineering levulinic acid (LA) utilization metabolic pathway and expressing heterologous PHA synthase (PhaEC), acetyl-CoA acetyltransferase (PhaA), and acetyl-CoA reductase (PhaB) in Pseudomonas putida EM42. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)], poly(3-hydroxyvalerate-co-4-hydroxyvalerate) [P(3HV-co-4HV)] and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) [P(3HB-co-3HV-co-4HV)] were produced by the natural LA pathway, poly(4-hydroxyvalerate) by lvaAB-deleted LA pathway, and P(3HV-co-4HV) and P(3HB-co-3HV-co-4HV) with relatively high 3HV by fadB-deleted LA pathway. PHA with different monomer fractions could be produced using different PHA synthases. Scl-PHA contents reached approximately 40% of cell dry mass under non-optimized flask culture. This demonstrates that the LA catabolic pathway may be a good alternative route to provide monomers for the production of various types of PHA.

Carbon dioxide sequestration by chemolithotrophic oleaginous bacteria for production and optimization of polyhydroxyalkanoate

The present work involved screening of a previously reported carbon concentrating oleaginous bacterial strain Serratia sp. ISTD04 for production of PHA and optimization of process parameters for enhanced PHA and biomass generation. The selected bacterial strain was screened for PHA production based on Nile red staining followed by visualization under fluorescence microscope. Spectrofluorometric measurement of Nile red fluorescence of the bacterial culture was also done. Confirmatory analysis of PHA accumulation by GC-MS revealed the presence of 3-hydroxyvalerate. Detection of characteristic peaks in the FT-IR spectrum further confirmed the production of PHA by the bacterium. Response Surface Methodology was used for optimization of pH and carbon sources' concentrations for higher PHA production. There was almost a 2 fold increase in the production of PHA following optimization as compared to un-optimized condition. The study thus establishes the production of PHA by Serratia sp. ISTD04.

Zobellella denitrificans strain MW1, a newly isolated bacterium suitable for poly(3-hydroxybutyrate) production from glycerol

AIMS

To search for new bacteria for efficient production of polyhydroxyalkanoates (PHAs) from glycerol.

METHODS AND RESULTS

Samples were taken from different environments in Germany and Egypt, and bacteria capable of growing in mineral salts medium with glycerol as sole carbon source were enriched. From a wastewater sediment sample in Egypt, a Gram-negative bacterium (strain MW1) was isolated that exhibited good growth and that accumulated considerable amounts of polyhydroxybutyrate (PHB) from glycerol and also from other carbon sources. The 16S rRNA gene sequence of this isolate exhibited 98.5% and 96.2% similarity to Zobellella denitrificans strain ZD1 and to Zobellella taiwanensis strain ZT1 respectively. The isolate was therefore affiliated as strain MW1 of Z. denitrificans. Strain MW1 grows optimally on glycerol at 41 degrees C and pH 7.3 and accumulated PHB up to 80.4% (w/w) of cell dry weight. PHB accumulation was growth-associated. Although it was not an absolute requirement, 20 g l(-1) sodium chloride enhanced both growth (5 g cell dry weight per litre) and PHB content (87%, w/w). Zobellella denitrificans strain MW1 is also capable to accumulate the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer if sodium propionate was used as cosubstrate in addition to glycerol.

CONCLUSIONS

A new PHB-accumulating strain was isolated and identified. This strain is able to utilize glycerol for growth and PHB accumulation to high content especially in the presence of NaCl that will enable the utilization of waste glycerol from biodiesel industry.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first report on accumulation of PHA in a member of the new genus Zobellella. Furthermore, utilization of glycerol as the sole carbon source for fast growth and PHB biosynthesis, growth in the presence of NaCl and high PHB contents of the cells will make this newly isolated bacterium a potent candidate for industrial production of PHB from crude glycerol occurring as byproduct during biodiesel production.

Production and characterization of homopolymer poly(3-hydroxyvalerate) (PHV) accumulated by wild type and recombinant Aeromonas hydrophila strain 4AK4

Aeromonas hydrophila 4AK4 normally produces copolyesters (PHBHHx) consisting of 3-hydroxybutyrate (C4) and 3-hydroxyhexanoate (C6). Wild type and recombinant A. hydrophila 4AK4 (pSXW02) expressing vgb and fadD genes encoding Vitreoscilla haemoglobin and Escherichia coli acyl-CoA synthase respectively, were found able to produce homopolyester poly(3-hydroxyvalerate) (PHV) (C5) on undecanoic acid as a single carbon source. The recombinant grew to 5.59 g/L cell dry weight (CDW) containing 47.74 wt% PHV in shake flasks when growth was conducted in LB medium and PHV production in undecanoic acid. The cells grew to 47.12 g/L CDW containing 60.08 wt% PHV in a 6 L fermentor study. Physical characterization of PHV produced by recombinant A. hydrophila 4AK4 (pSXW02) in fermentor showed a weight average molecular weight (M(w)) of 230,000 Da, a polydispersity of 3.52, a melting temperature of 103 degrees C and a glass transition temperature of -15.8 degrees C. The degradation temperature at 5% weight loss of the PHV was around 258 degrees C.

Development of a process for the biotechnological large-scale production of 4-hydroxyvalerate-containing polyesters and characterization of their physical and mechanical properties

A process for the large-scale production of 4-hydroxyvalerate (4HV)-containing biopolyesters with a new monomer composition was developed by means of high-cell-density cultivation applying recombinant strains of Pseudomonas putida and Ralstonia eutropha, harboring the PHA-biosynthesis genes phaC and phaE of Thiocapsa pfennigii. Cell densities of about 20 g/L revealing a PHA content of 52% (w/w) and a molar fraction of 4HV of up to 15.4 mol % were obtained by a two-stage fed-batch cultivation process at a 25-L scale using octanoic acid during the growth phase and levulinic acid for the accumulation of 4HV-containing polyesters. Besides 4HV the polyester contained significant amounts of both 3-hydroxybutyric acid (3HB) and 3-hydroxyvaleric acid (3HV) and traces of 3-hydroxyhexanoic acid (3HHx) and 3-hydroxyoctanoic acid (3HO). With glucose or gluconic acid as the growth substrate, the components of the polyester could be reduced to mainly 3HV and 4HV with only a negligible fraction of 3HB, resulting in a polyester with a new composition. Scale-up of the cultivation process to a 500-L scale was successfully performed, resulting in the production of these polyesters at a pilot plant scale. Short-term shifts in temperature and pH resulted in the formation of cell agglomerates of about 50-100 microm by which the effectiveness of the semicontinuous centrifugation process was drastically increased. Washing of the freeze-dried cells with boiling methanol significantly shortened the extraction process and resulted in a polyester of higher purity. The physical and mechanical properties of these copolyesters were characterized by means of size exclusion chromatography, dynamic mechanical analysis, differential scanning calorimetry, stress-strain measurements, and measurements of the viscosity of the solution. The copolyesters were cast into films, spun to fibers, or processed into test bars by melt spinning and injection molding, respectively. They revealed an almost entirely amorphous structure and consequently were sticky and lacked strength. However they showed high thermal stability and an unusually high elongation at break of about 200%; the molecular weights (M(w)) were between 2.0 x 10(5) and 3.3 x 10(5) g/mol. It was shown that 4HV-containing polyesters belong to the class of thermoplastic elastomeres.

Production of microbial polyesters: fermentation and downstream processes

Poly(3-hydroxyalkanoates) (PHAs) constitute a large and versatile family of polyesters produced by various bacteria. PHAs are receiving considerable attention because of their potential as renewable and biodegradable plastics, and as a source of chiral synthons since the monomers are chiral. Industrial PHA production processes have been developed for poly(3-hydroxybutyrate) (poly(3HB)) and poly(3-hydroxybutyrate-co-3-valerate) (poly(3HB-co-3HV). More than 100 other poly(3HAMCL)s, characterized by monomers of medium chain length, have been identified in the past two decades. These monomers typically contain 6-14 carbon atoms, are usually linked via-3-hydroxy ester linkages, but can occasionally also exhibit 2-, 4-, 5-, or 6-hydroxy ester linkages. Such polyesters are collectively referred to as medium chain length PHAs poly(3HAMCL)s. The vast majority of these interesting biopolyesters have been studied and produced only on the laboratory scale. However, there have been several attempts to develop pilot scale processes, and these provide some insight into the production economics of poly(3HAMCL)s other than poly(3HB) and poly(3HB-co-3HV). These processes utilize diverse fermentation strategies to control the monomer composition of the polymer, enabling the tailoring of polymer material properties to some extent. The best studied of these is poly(3-hydroxyoctanoate) (poly(3HO)), which contains about 90% 3-hydroxyoctanoate. This biopolyester has been produced on the pilot scale and is now being used in several experimental applications.

Perspectives of medium chain length poly(hydroxyalkanoates), a versatile set of bacterial bioplastics

Medium chain length (mcl) poly(hydroxyalkanoic acids) (PHAs) are polyesters accumulated by fluorescent Pseudomonads and other bacteria. Work on the genetics of mcl-PHA formation has led to polymer synthesis in recombinant bacteria and plants. Several high and medium cost applications are now emerging. With optimized bacterial mcl-PHA synthesis on inexpensive agro-substrates and the development of plant-based mcl-PHAs in the next decade, the production economics of these bioplastics will ultimately permit their sustainable production for bulk applications.

Bacterial and other biological systems for polyester production

Poly(3-hydroxybutyric acid) and other structurally related aliphatic polyesters from bacteria, referred to as polyhydroxyalkanoic acids, form biodegradable thermoplastics and elastomers that are currently in use, or being considered for use, in industry, medicine, pharmacy and agriculture. At present, they are produced by microbial fermentations; in the future, production will also be possible by in vitro methods or by agriculture using transgenic plants. Representatives from this highly diverse class of polyesters might be produced as commodity chemicals for bulk applications, and others as fine chemicals for special applications.