Properties Of Polyhydroxybutyrate Research Articles

Physicochemical characterization of polyhydroxybutyrate (PHB) produced by the rare halophile Brachybacterium paraconglomeratum MTCC 13074

BackgroundPolyhydroxybutyrate is a biopolymer produced by bacteria and archaea under nitrogen-limiting conditions. PHB is an essential polymer in the bioplastic sector because of its biodegradability, eco-friendliness, and adaptability. The characterization of PHB is a multifaceted process for studying the structure and its properties. This entire aspect can assure the long-term viability and performance attributes of the PHB. The characteristics of PHB extracted from the halophile Brachybacterium paraconglomeratum were investigated with the objective of making films for application in healthcare.ResultsThis was the first characterization study on PHB produced by a rare halophile, Brachybacterium paraconglomeratum (MTCC 13074). In this study, the strain produced 2.72 g/l of PHB for.5.1 g/l of biomass under optimal conditions. Methods are described for the determination of the physicochemical properties of PHB. The prominent functional groups CH3 and C = O were observed by FT-IR and the actual chemical structure of the PHB was deduced by NMR. GCMS detects the confirmation of four methyl ester derivatives of the extracted PHB in the sample. Mass spectrometry revealed the molecular weight of methyl 3-hydroxybutyric acid (3HB) present in the extract. The air-dried PHB films were exposed to TGA, DSC and a universal testing machine to determine the thermal profile and mechanical stability. Additionally, the essential property of biopolymers like viscosity was also assessed for the extracted PHB.ConclusionsThe current study demonstrated the consistency and quality of B. paraconglomeratum PHB. Therefore, Brachybacterium sps are also a considerable source of PHB with desired characteristics for industrial production.

Impact of Multiple Reprocessing on Properties of Polyhydroxybutyrate and Polypropylene.

Biobased plastics have the potential to be sustainable, but to explore their circularity further, current end-of-life options need to be broadened. Mechanical recycling is one of the most accepted methods to bring back plastics into the loop. Polyhydroxybutyrates (PHBs) are biobased and biodegradable in nature with promising properties and varied applications in the market. This study focuses on their potential for mechanical recycling by multiple extrusion cycles (E1-E5) and multi-faceted characterization of the virgin (V) and reprocessed materials from E1 to E5. The behavior is compared to polypropylene (PP) as a reference with a similar property profile, which has also been reprocessed five times. The thermal properties of both series showed a stable melting point and thermal decomposition temperature from thermal analyses (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)). However, a steady increase in the degree of crystallinity was observed which could counterbalance the decrease in molecular weight due to repeated extrusion measured by gel permeation chromatography and resulted in similar values of tensile strength across the cycles. The strain at break was impacted after the first extrusion, but no significant change was observed thereafter; the same was observed for impact strength. Even in scanning electron microscopy (SEM) images, virgin and E5 samples appeared similar, showing the stability of morphological characteristics. Fourier transform infrared spectroscopy (FTIR) results revealed that no new groups are being formed even on repeated processing. The deviation between the PHB and PP series was more predominant in the melt mass flow rate (MFR) and rheology studies. There was a drastic drop in the MFR values in PHB from virgin to E5, whereas not much difference was observed for PP throughout the cycles. This observation was corroborated by frequency sweeps conducted with the parallel plate method. The viscosity dropped from virgin to E1 and E2, but from E3 to E5 it presented similar values. This was in contrast to PP, where all the samples from virgin to E5 had the same values of viscosity. This paper highlights the possibilities of mechanical recycling of PHB and explains why future work with the addition of virgin material and other additives is an area to be explored.

Polyhydroxybutyrate Metabolism in Azospirillum brasilense and Its Applications, a Review.

Gram-negative Azospirillum brasilense accumulates approximately 80% of polyhydroxybutyrate (PHB) as dry cell weight. For this reason, this bacterium has been characterized as one of the main microorganisms that produce PHB. PHB is synthesized inside bacteria by the polymerization of 3-hydroxybutyrate monomers. In this review, we are focusing on the analysis of the PHB production by A. brasilense in order to understand the metabolism during PHB accumulation. First, the carbon and nitrogen sources used to improve PHB accumulation are discussed. A. brasilense accumulates more PHB when it is grown on a minimal medium containing a high C/N ratio, mainly from malate and ammonia chloride, respectively. The metabolic pathways to accumulate and mobilize PHB in A. brasilense are mentioned and compared with those of other microorganisms. Next, we summarize the available information to understand the role of the genes involved in the regulation of PHB metabolism as well as the role of PHB in the physiology of Azospirillum. Finally, we made a comparison between the properties of PHB and polypropylene, and we discussed some applications of PHB in biomedical and commercial areas.

PHB Processability and Property Improvement with Linear-Chain Polyester Oligomers Used as Plasticizers.

In 2021, global petroleum-based plastic production reached over 400 million metric tons (Mt), and the accumulation of these non-biodegradable plastics in the environment is a worldwide concern. Polyhydroxybutyrate (PHB) offers many advantages over traditional petroleum-based plastics, being biobased, completely biodegradable, and non-toxic. However, its production and use are still challenging due to its low deformation capacity and narrow processing window. In this work, two linear-chain polyester oligomers were used as plasticizers to improve the processability and properties of PHB. Thermal analyses, XRD, and polarized optical microscopy were performed to evaluate the plasticizing effect on the PHB and the reflection on the mechanical behavior. Both oligomers acted as PHB plasticizers, with a reduction in Tg and Tm as a function of the plasticizer concentration, which can make it easier to handle the material in thermal processing and reduce the probability of thermal degradation. Plasticizer 2 proved to be the most promising between the two with an optimized condition of 20%, in which there was a decrease in elastic modulus of up to 72% and an increase in the maximum elongation of 467%.

Finding a Benign Plasticizer to Enhance the Microbial Degradation of Polyhydroxybutyrate (PHB) Evaluated by PHB Degrader Microbulbifer sp. SOL66

As a biodegradable plastic, polyhydroxybutyrate (PHB) has relatively poor mechanical properties, preventing its wider use. Various plasticizers have been studied to improve the mechanical properties of PHB; however, due to the slow degradation speed in the soil environment and lack of evaluation methods, studies on the degradation of PHB with plasticizers are rarely reported. In this study, by applying Microbulbifer sp. SOL66, which is able to degrade PHB very quickly, a benign plasticizer was evaluated with good properties and good degradability, not inhibiting microbial activities. Eight different plasticizers were applied with PHB and Microbulbifer sp. SOL66, PHB film containing 10% and 20% tributyl citrate showed significant biodegradability of PHB. It was confirmed that tributyl citrate could increase the speed of PHB degradation by Microbulbifer sp. SOL66 by 88% at 1 day, although the degree of degradation was similar after 3 days with and without tributyl citrate. By the analysis of microbial degradation, physical, chemical, and mechanical properties, tributyl citrate was shown not only to improve physical, chemical, and mechanical properties but also the speed of microbial degradation.

Optimization and characterization of polyhydroxybutyrate/lignin electro-spun scaffolds for tissue engineering applications

The tissue engineering scaffolds requires efficient combination of materials, appropriate method of preparation, and precise characterization of final product. In this study, the optimal electrospinning process conditions of polyhydroxybutyrate (PHB) were investigated by Taguchi design. Then, the initial PHB solution characteristics in the presence of lignin were optimized and then electro-spun. In this regard, the uniformity of electro-spun nanofibers, observed by SEM, confirmed that 9 w/v % is the optimum concentration of PHB in Trifluoro acetic acid. Addition of 6 wt% of lignin to PHB, could alleviate both the brittleness and hydrophobicity of PHB, as DSC, XRD, and WCA results indicated decrement in crystallinity (from 46 to 39 %), crystal size (from 21.8 to 15.2 nm), and WCA (from 118 to 73°). On the other hand, FESEM results represented diameter reduction from 1318 ± 202.07 to 442 ± 111.04 nm, and transformation of nanofiber physical structure from ribbon-like to cylindrical fiber by adding lignin. In addition, the mechanical properties of PHB including elongation at break, toughness, young modulus, and tensile strength were also improved (up to twice) by adding lignin. Ultimately, reviewing the outputs of degradation, bioactivity, MG63 cell viability, proliferation, mineralization, and antioxidant activity confirm that PHB/lignin electrospun scaffold has potential application in tissue engineering.

Production and characterization of polyhydroxybutyrate (PHB) BY Burkholderia cepacia BPT1213 using waste glycerol as carbon source

This study focused on the utilization of waste glycerol, a by-product of the biodiesel industry, used as a carbon source to grow Burkholderia cepacia BPT1213 for the production of PHB. B. cepacia BPT1213 was cultivated in minimal salt media (MSM) supplemented with waste glycerol at concentrations ranging from 2% to 9% (v/v). A gradual decrease was depicted by the cell dry weight (CDW) and PHB content with increasing waste glycerol content. B. cepacia BPT1213 is able to synthesize and accumulate up to 2.41 g/L and 66.4% dry biomass and PHB yield respectively when supplemented with 2% (v/v) waste glycerol. This resulted in a total PHB concentration of 1.6 g/L. The characterization of extracted PHB was carried out by Nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR) for structural composition evaluation. Both analyses showed expected signals for PHB as reported in other studies which depicted the methyl, methylene and methine groups for NMR analyses, and certain functional groups which were the hydroxyl group, carbonyl stretch and ester group for FTIR. This study demonstrated the effects of waste glycerol concentration on the end properties of PHB, which is an important aspect for its applications.

Polyhydroxybutyrate/polylactic acid blends: An alternative feedstock for 3D printed bone scaffold model

In this research, we developed 3D printing filaments from polyhydroxybutyrate (PHB)/poly(lactic acid) (PLA) blends to further its use in a fused filament fabrication (FFF) 3D printing technique as an alternative feedstock for manufacturing bone scaffold model. The filaments were fabricated with blending ratios of PHB/PLA at 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100 %wt. using an extrusion process. Furthermore, 10 phr of polypropylene glycol (PPG) was added as a processing aid to enhance the processability. The results of MFR showed that the suitable temperature for 3D printing of all blended filaments is 190 °C. The changes in thermal properties indicate the partial compatibility between PHB and PLA in the blends. PLA plays a vital role in improving the mechanical properties of PHB. 3D printing filament from PHB/PLA blends has been successfully developed.

Structural assessment of the bioplastic (poly-3-hydroxybutyrate) produced by Bacillus flexus Azu-A2 through cheese whey valorization

The demand for the production of biodegradable plastics has significantly increased. Bioplastics have become an essential alternative to the threats of the daily consumable plastics, sourced from fossil fuels, to the environment. Polyhydroxyalkonates (PHAs) are a ubiquitous group of bioderived and biodegradable plastics, however their production is limited by the costs associated mainly with the carbon sources. Herein, this study aims to reduce the PHAs production cost by using a by-product from the dairy industry, i.e., cheese whey (CW), as a sole carbon source. The developed process recruits an aquatic isolate, Bacillus flexus Azu-A2, and is optimized via studying various parameters using the shaking flasks technique. The results showed that the maximum PHA production (0.95 g L-1) and PHA content (20.96%, w/w), were obtained after incubation period 72 h at 45 °C, 100 rpm agitation rate, 50% CWS concentration, pH 8.5, and 1.0 g L-1 ammonium chloride. Physiochemically, Fourier transform infrared spectroscopy (FTIR), gas chromatography-mass spectroscopy (GC–MS), nuclear magnetic resonance (NMR), and energy-dispersive X-ray (EDX) techniques, emphasized the type of the extracted PHA as polyhydroxybutyrate (PHB). The thermal properties of PHB were measured using differential scanning calorimetry (DSC), recording melting transition temperature (Tm) at 170.96 °C. Furthermore, a scanning electron microscope (SEM) visualized a homogenous microporous structure for the thin PHB biofilm. In essence, this study highlights the ability of Bacillus flexus Azu-A2 to produce a good yield of highly purified PHB at reduced production cost from dairy CW. Consequently, the current study paves the way for an improved whey management strategy.

Biosynthesis of Polyhydroxybutyrate with Cellulose Nanocrystals Using Cupriavidus necator.

Polyhydroxybutyrate (PHB) is a natural polyester synthesized by several microorganisms. Moreover, it has excellent biodegradability and is an eco-friendly material because it converts water and carbon dioxide as final decomposition products. However, the applications of PHB are limited because of its stiffness and brittleness. Because cellulose nanocrystals (CNCs) have excellent intrinsic mechanical properties such as high specific strength and modulus, they may compensate for the insufficient physical properties of PHB by producing their nanocomposites. In this study, natural polyesters were extracted from Cupriavidus necator fermentation with CNCs, which were well-dispersed in nitrogen-limited liquid culture media. Fourier-transform infrared spectroscopy results revealed that the additional O–H peak originating from cellulose at 3500–3200 cm−1 was observed for PHB along with the C=O and –COO bands at 1720 cm−1. This suggests that PHB–CNC nanocomposites could be readily obtained using C. necator fermented in well-dispersed CNC-supplemented culture media.

Production of blue-colored polyhydroxybutyrate (PHB) by one-pot production and coextraction of indigo and PHB from recombinant Escherichia coli

Polyhydroxyalkanoate (PHA) is a promising substitute for petroleum-based plastics. For economically feasible and sustainable production of PHA, various strains and feedstocks have been reported till date, using which, polyhydroxybutyrate (PHB) could be produced on a large scale. However, the sensory characteristics of PHA, such as color, limit its further application in industries related to packaging, textiles, and medical materials. In this study, we investigated the feasibility of simultaneous production of indigo and PHB in recombinant Escherichia coli to generate colored bioplastics. With that objective, one-pot production and extraction of both indigo and PHB were successfully performed, and biotransformation of indole to indigo was reinforced by the introduction of PHA synthetic genes. Upon further investigation of the factors responsible for the increased indigo production, groEL and grpE, related to heat-shock proteins, and CYP102G4, were found to be up-regulated when analyzed by semi-quantitative reverse transcription-PCR. In the thermograms analyzed by thermal gravimetric analysis and differential scanning calorimetry, there was no notable difference between PHB and PHB-indigo film, implying that indigo did not affect the thermal properties of PHB itself. Overall, this study demonstrates the production of blue-colored PHB and enhanced production of indigo by the introduction of PHA synthetic genes.

Cellulose nanofibrils and nano-scaled titanium dioxide-reinforced biopolymer nanocomposites: Selecting the best nanocomposites with multicriteria decision-making methods

The aim of the paper is to determine the effects of nano fillers such as cellulose nanofibrils and nano-scaled titanium dioxide on some properties of polyhydroxybutyrate and polylactic acid biopolymers; it also determined the selection of biopolymer nanocomposites with the optimum properties by using multicriteria decision-making methods such as multi-attribute utility theory, simple additive weighting, and weighted aggregated sum product assessment. Test results showed that the mechanical properties of the biopolymer nanocomposites generally increased with the addition of the cellulose nanofibrils and nano-scaled titanium dioxide. However, the addition of nano-scaled titanium dioxide decreased the tensile modulus. The addition of the cellulose nanofibrils had a higher effect on the tensile and flexure modulus of elasticity than the addition of the nano-scaled titanium dioxide. Thermal properties were generally found to improve with the addition of the cellulose nanofibrils and nano-scaled titanium dioxide. Melting temperature (Tm) generally decreased with the addition of the nano fillers. The scanning electron microscopic images showed that the nano fillers were dispersed as white dots in the biopolymer matrix. After accelerated weathering and decay test, outdoor performance of the biopolymer nanocomposites was found to be improved with the addition of the nano fillers. Multicriteria decision-making methods were conducted to determine the biopolymer nanocomposites having the optimum properties, and all the methods showed that the best biopolymer nanocomposites was polylactic acid with 1% cellulose nanofibrils.

Influence of Epoxidized Canola Oil (eCO) and Cellulose Nanocrystals (CNCs) on the Mechanical and Thermal Properties of Polyhydroxybutyrate (PHB)-Poly(lactic acid) (PLA) Blends.

Two major obstacles to utilizing polyhydroxybutyrate (PHB)—a biodegradable and biocompatible polymer—in commercial applications are its low tensile yield strength (<10 MPa) and elongation at break (~5%). In this work, we investigated the modification of the mechanical properties of PHB through the use of a variety of bio-derived additives. Poly(lactic acid) (PLA) and sugarcane-sourced cellulose nanocrystals (CNCs) were proposed as mechanical reinforcing elements, and epoxidized canola oil (eCO) was utilized as a green plasticizer. Zinc acetate was added to PHB and PLA blends in order to improve blending. Composites were mixed in a micro-extruder, and the resulting filaments were molded into 2-mm sheets utilizing a hot-press prior to characterization. The inclusion of the various additives was found to influence the crystallization process of PHB without affecting thermal stability. In general, the addition of PLA and, to a lesser degree, CNCs, resulted in an increase in the Young’s modulus of the material, while the addition of eCO improved the strain at break. Overall, samples containing eCO and PLA (at concentrations of 10 wt %, and 25 wt %, respectively) demonstrated the best mechanical properties in terms of Young’s modulus, tensile strength and strain at break.

Development and characterization of polyhydroxybutyrate biocomposites and their application in the removal of heavy metals

Polyhydroxybutyrate (PHB) is the well-known polyhydroxyalkanoate (PHA) accumulated by many bacterial species under conditions of nutrient limitation. General applications of PHB and its composites include food packaging, agriculture, medicine, drug delivery, tissue engineering, etc. Herein, we report biosynthesis of PHB from Bacillus cereus using both chemical and physical extraction methods. As a result, the physical method (0.451 g/L) was found to be advantageous when compared to chemical method (0.345 g/L). In order to improve the properties of PHB, it was blended with polyethylene glycol (PEG) and starch to obtain biocomposites viz., PHB-PEG 4000, PHB-PEG 6000 and PHB-Starch. The obtained PHB and its biocomposites were characterized by FTIR, TGA/ DSC, SEM and XRD techniques. FTIR spectroscopy results showed the vibrational frequencies for all the expected functional groups. The thermal studies revealed that the composites are thermally stable than pure PHB. The SEM images showed highly porous structure of PHB-Starch composite when compared to PHB-PEG composites. The crystalline nature of PHB and its composites were confirmed from powder XRD patterns. The application of these biocomposites in the removal of heavy metals was demonstrated by successful adsorption of Pb2+ ion from aqueous solution in a batch process mode.

1-Ethyl-3-methylimidazolium Diethylphosphate Based Extraction of Bioplastic “Polyhydroxyalkanoates” from Bacteria: Green and Sustainable Approach

An eco-friendly approach toward downstream processing of bacterial biomass for extraction of an intracellular potential bioplastic material polyhydroxyalkanoates replacing chlorinated organic solvents is reported using ionic liquid (IL) 1-ethyl-3-methylimidazolium diethylphosphate ([C2mim][(C2)2OPO3]) as an extractant. [C2mim][(C2)2OPO3] dissolved wet bacterial biomass of Halomonas hydrothermalis (MTCC accession no. 5445; NCBI Genbank accession no. GU938192), with ease on account of its high hydrogen bond basicity (β = 1.07). The recovered polymer with a yield of 60% ± 2% was characterized using 1H NMR, FT-IR, and TGA techniques and confirmed to be polyhydroxybutyrate (PHB). The properties of PHB were found to be in close proximity to the standard PHB. The [C2mim][(C2)2OPO3] was recovered with 60% yield and retention of chemical structure after two consecutive dissolution cycles, which minimized the cost of developed process. The recovered PHB was used to prepare a bioplastic film, which showed good therm...

Microbial production, ultrasound-assisted extraction and characterization of biopolymer polyhydroxybutyrate (PHB) from terrestrial (P. hysterophorus) and aquatic (E. crassipes) invasive weeds

This study reports synthesis of biodegradable poly(3-hydroxybutyrate) (PHB) polymer from two invasive weeds, viz. P. hysterophorus and E. crassipes. The pentose and hexose-rich hydrolyzates obtained from acid pretreatment and enzymatic hydrolysis of two biomasses were separately fermented using Ralstonia eutropha MTCC 8320 sp. PHB was extracted using sonication and was characterized using FTIR, 1H and 13C NMR and XRD. PHB content of dry cell mass was 8.1–21.6% w/w, and the PHB yield was 6.85×10−3–36.41×10−3% w/w raw biomass. Thermal properties of PHB were determined by TGA, DTG and DSC analysis. PHB obtained from pentose-hydrolyzate had glass transition temperatures of 6°–9°C, while PHB from hexose-rich hydrolyzate had maximum thermal degradation temperatures of 370°–389°C. These thermal properties were comparable to the properties of commercial PHB. Probable causes leading to differences in thermal properties of pentose and hexose-derived PHB are: extent of crystallinity and presence of impurity in the polymer matrix.

Biocomposites from polyhydroxybutyrate and bio-fillers by solvent casting method

Biocomposites from polyhydroxybutyrate (PHB) and some bio-fillers such as lignin (L), alpha cellulose (AC) and cellulose nanofibrils (CNFs) were prepared to investigate the effect of the bio-fillers on the properties of PHB by a solvent casting method. The thermal properties by thermogravimetry analysis (TGA–DTG and DTA) and differential scanning calorimetry (DSC) were determined; morphological characterization by scanning electron microscopy (SEM) and structural analysis by X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) of the biocomposites were performed. TGA curves showed that the highest values for T 10%, T 50% of the biocomposites were 278.2∘C for PHB+2%AC and 291.7∘C for PHB+2%CNFs; however, the best value for T 75% was obtained as 381.5∘C for PHB+2%L. According to DTG curves, the best results were found for PHB+0.5%L and PHB+0.5%CNFs. DTA showed an increase in temperature of maximum degradation with loading of lignin and CNFs. The addition of bio-fillers increases T c and T m for both first cooling/heating and second cooling/heating. T c and T m values for first cooling/healing were found to be lower as compared with second cooling/healing. Furthermore, the addition of bio-fillers acts as a nucleating agent in PHB and SEM pictures showed the porous structure in all biocomposites. SEM images revealed uniform distribution of the reinforcing particles in the polymer at low loadings (0.5 wt%), while higher loadings (2 wt%) of L and CNFs contributed to easy aggregation within the PHB matrix. In XRD studies, PHB in the range 5–55∘ shows 6 main peaks. XRD patterns of the PHB biocomposites revealed 3 main peaks at 13.57∘, 16.87∘ and 22.1∘, and the other peaks disappeared in the patterns. The largest and lowest values of X c were found for PHB+2%AC and PHB+2%CNFs, respectively.

Production of Bio-plastics (Polyhydroxy Butyrate) from Industrial Effluent using Batch and Two Stage Batch Culture Studies

The present study focuses on the improvement of production of Poly Hydroxy Butyrate (PHB) using Bacillus megaterium MTCC 8075. The culture media and conditions were studied critically and was found that the maximum PHB production was attained in the presence of glucose as carbon source at 6% concentration with a yield of 55.0 mg/g cell weight and peptone as nitrogen source with a yield of 17.2mg/g cell weight. The optimum pH was found to be 7(22.8mg/g) and it was also investigated that PHB production was maximum corresponding to a temperature of 35°C (35.46mg/g) and at an incubation time of 72 hours (52.2mg/g). PHB was qualitatively analysed using Sudan Black staining method, extracted using sodium hypochlorite, and quantified using crotonic acid assay in UV spectrophotometer at a wavelength of 235nm. PHB production was carried out in various selected effluents like corn stalk waste and petroleum refinery effluent and corn corb yielded the maximum PHB production of 3.1mg/L. The produced PHB was confirmed using Fourier Transform Infrared (FTIR) analysis and NMR spectroscopic studies. PHB production was further improved using two-stage batch culture studies in which PHB production was compared in various nutrient limited conditions of nitrogen and phosphorous. The thermal properties of PHB was studied using Differential Scanning Calorimetry(DSC) and Thermogravimetric Analysis (TGA).

Effect of Clamshells Filler Loading on the Tensile Properties of Polyhydroxybutyrate

In this study, the abundant availability of clamshell, as the potential of the biomass resources for the production of the inorganic filler such as calcium carbonate (CaCO3) and calcium oxide (CaO) is fully utilized. In addition, the effect of filler loadings toward mechanical properties of polyhydroxybutyrate (PHB) biopolymer was studied using various ranges of loadings such as 10, 20, 30, 40 and 50 wt%. The tensile strength and modulus of PHB showed significant improvement with the incorporation of the filler up to 30 wt %, and this finding was supported by micrographs obtained from scanning electron microscope (SEM) which revealed uniform distribution of the filler in the polyhydroxybutyrate region. However, the elongations at break of the specimen shows vice versa, they start to deteriorate with the addition of the filler.

Sustainable autotrophic production of polyhydroxybutyrate (PHB) from CO2 using a two-stage cultivation system

The technical feasibility of Cupriavidus necator DSM 545 for sustainable autotrophic polyhydroxybutyrate (PHB) production from CO2 using a two-stage cultivation system was evaluated. In this cultivation method, cell mass growth occurred under heterotrophic conditions using two different organic substrates, namely glucose and waste glycerol. In both cases, PHB biosynthesis was triggered by applying nitrogen and oxygen limitation at three different cell mass concentrations under autotrophic conditions using a gas mixture of H2, O2 and CO2. To ensure that the test conditions were relevant for later industrial application, O2 concentration was kept below the safety value during autotrophic PHB production. PHB production from CO2 on waste-glycerol grown cell mass resulted in a PHB concentration of 28g/L, which is the highest reported value in literature for PHB synthesized from CO2 at an O2 concentration below the lower explosion limit of 5vol%. The fermentation performance decreased when nutrient limitation was delayed at higher cell mass concentrations. Furthermore, it was shown that PHB production from CO2 at high cell mass concentration is metabolically feasible, but under the tested conditions the mass transfer of O2 was limiting PHB accumulation. Characterization of the produced polymers showed that the organic carbon source affected the properties of PHB and that the cultivation method developed in this study provided PHB with properties similar to a commercial PHB and PHB typically found in literature. It can be concluded that heterotrophic–autotrophic production of PHB by C. necator is a promising cultivation method to reduce the overall production cost of PHB. In order to compete with the current heterotrophic cultivation system, the oxygen transfer rate must however be enhanced to achieve a higher PHB productivity.