Evaluation of by-products from the biodiesel industry as fermentation feedstock for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production by Cupriavidus necator

Exploiting latent microbial potentials for producing polyhydroxyalkanoates: A holistic approach

Plastics are versatile, however, nonbiodegradable polymers that are primarily derived from fossil fuels and pose notable environmental challenges. However, biopolymers, such as polyhydroxyalkanoates (PHAs), poly(lactic acid), starch, and cellulose have emerged as sustainable alternatives to conventional plastics. Among these, PHAs stand out as strong contenders as they are completely bio-based and biodegradable and are synthesized by microbes as an energy reserve under stress conditions. Despite their limitations, including low mechanical strength, susceptibility to degradation, a restricted scope of application, and high production costs, biopolymers have promising potential. This review explores strategies for enhancing PHA production to address these challenges, emphasizing the need for sustainable PHA production. These strategies include selecting robust microbial strains and feedstock combinations, optimizing cell biomass and biopolymer yields, genetically engineering biosynthetic pathways, and improving downstream processing techniques. Additives such as plasticizers, thermal stabilizers, and antioxidants are crucial for modifying PHA characteristics, and its processing for achieving the desired balance between processability and end-use performance. By overcoming these complications, biopolymers have become more viable, versatile, and eco-friendly alternatives to conventional plastics, offering hope for a more sustainable future.

Corn or Soybean Oil as the Sole Carbon Source for Polyhydroxybutyrate Production in a Biofuel Biorefinery Concept

The use of polyhydroxybutyrate (PHB) can help diminish fossil chemical dependency because it can partially replace petrochemical plastics due to its biodegradability and similar mechanical properties. However, its production costs are high compared with fossil-based plastics. Alternative carbon sources can be used in the fermentation media because they are renewable and low-cost. Vegetable oils are especially attractive due to their high carbon content, contributing to high production rates per gram of substrate. This work aimed to produce PHB from Cupriavidus necator LPB1421 using either corn or soybean oil as the sole carbon source. Urea was the best nitrogen source, enabling a DCW production of 4.35 g/L (corn oil) and 10.4 g/L (soybean oil). After media optimization, the DCW of corn oil reached 22.13 g/L, with 57.46% PHB accumulation (12.71 g PHB/L), whereas soybean oil led to a DCW of 19.83 g/L, with 54.91% PHB accumulation (10.89 g PHB/L). This media composition was employed in a kinetics assay, revealing similar fermentation parameters among both oils and a yield of 0.2118 g PHB/g for corn oil and 0.1815 g PHB/g for soybean oil. These results open the possibility of integrating PHB production with biofuel manufacturing in a bioethanol/biodiesel biorefinery concept.

Materials designed to degrade: structure, properties, processing, and performance relationships in polyhydroxyalkanoate biopolymers

Conventional plastics pose significant environmental and health risks across their life cycle, driving intense interest in sustainable alternatives. Among these, polyhydroxyalkanoates (PHAs) stand out for their biocompatibility, degradation characteristics, and diverse applications. Yet, challenges like production cost, scalability, and limited chemical variety hinder their widespread adoption, impacting material selection and design. This review examines PHA research through the lens of the classical materials tetrahedron, exploring property-structure-processing-performance (PSPP) relationships. By analyzing recent literature and addressing current limitations, we gain valuable insights into PHA development. Despite challenges, we remain optimistic about the role of PHAs in transitioning towards a circular plastic economy, emphasizing the need for further research to unlock their full potential.

Innovations in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and nanocomposites for sustainable food packaging via biochemical biorefinery platforms: A comprehensive review

The substantial build-up of non-biodegradable plastic waste from packaging sector not only poses severe environmental threats but also hastens the depletion of natural petroleum-based resources. Presently, poly (3-hydroxybutyrate-co-3-hydroxy valerate) (PHBV), received enormous attention as ideal alternatives for such traditional petroleum-derived plastics based on their biocompatibility and superior mechanical properties. However, high cost of such copolymer, due to expensive nature of feedstock, inefficient microbial processes and unfavorable downstream processing strategies restricts its large-scale commercial feasibility in the packaging sector. This review explores merits and challenges associated with using potent agricultural and industrial waste biomasses as sustainable feedstocks alongside improved fermentation and downstream processing strategies for the biopolymer in terms of biorefinery concept. Despite PHBV's attractive properties, its inherent shortcomings like weak thermal stability, poor mechanical properties, processability difficulty, substantial hydrophobicity and comparatively higher water vapor permeability (WVP) demand the development of its composites based on the application. Based on this fact, the review assessed properties and potential applications of PHBV-based composite materials having natural raw materials, nanomaterials and synthetic biodegradable polymers. Besides, the review also enlightens sustainability, future prospects, and challenges associated with PHBV-based composites in the field of food packaging while considering insights about economic evaluation and life cycle assessment.

A Review of Current Achievements and Recent Challenges in Bacterial Medium-Chain-Length Polyhydroxyalkanoates: Production and Potential Applications

Using petroleum-derived plastics has contributed significantly to environmental issues, such as greenhouse gas emissions and the accumulation of plastic waste in ecosystems. Researchers have focused on developing ecofriendly polymers as alternatives to traditional plastics to address these concerns. This review provides a comprehensive overview of medium-chain-length polyhydroxyalkanoates (mcl-PHAs), biodegradable biopolymers produced by microorganisms that show promise in replacing conventional plastics. The review discusses the classification, properties, and potential substrates of less studied mcl-PHAs, highlighting their greater ductility and flexibility compared to poly(3-hydroxybutyrate), a well-known but brittle PHA. The authors summarize existing research to emphasize the potential applications of mcl-PHAs in biomedicine, packaging, biocomposites, water treatment, and energy. Future research should focus on improving production techniques, ensuring economic viability, and addressing challenges associated with industrial implementation. Investigating the biodegradability, stability, mechanical properties, durability, and cost-effectiveness of mcl-PHA-based products compared to petroleum-based counterparts is crucial. The future of mcl-PHAs looks promising, with continued research expected to optimize production techniques, enhance material properties, and expand applications. Interdisciplinary collaborations among microbiologists, engineers, chemists, and materials scientists will drive progress in this field. In conclusion, this review serves as a valuable resource to understand mcl-PHAs as sustainable alternatives to conventional plastics. However, further research is needed to optimize production methods, evaluate long-term ecological impacts, and assess the feasibility and viability in various industries.

Organic waste-to-bioplastics: Conversion with eco-friendly technologies and approaches for sustainable environment

Petrochemical-based synthetic plastics poses a threat to humans, wildlife, marine life and the environment. Given the magnitude of eventual depletion of petrochemical sources and global environmental pollution caused by the manufacturing of synthetic plastics such as polyethylene (PET) and polypropylene (PP), it is essential to develop and adopt biopolymers as an environment friendly and cost-effective alternative to synthetic plastics. Research into bioplastics has been gaining traction as a way to create a more sustainable and eco-friendlier environment with a reduced environmental impact. Biodegradable bioplastics can have the same characteristics as traditional plastics while also offering additional benefits due to their low carbon footprint. Therefore, using organic waste from biological origin for bioplastic production not only reduces our reliance on edible feedstock but can also effectively assist with solid waste management. This review aims at providing an in-depth overview on recent developments in bioplastic-producing microorganisms, production procedures from various organic wastes using either pure or mixed microbial cultures (MMCs), microalgae, and chemical extraction methods. Low production yield and production costs are still the major bottlenecks to their deployment at industrial and commercial scale. However, their production and commercialization pose a significant challenge despite such potential. The major constraints are their production in small quantity, poor mechanical strength, lack of facilities and costly feed for industrial-scale production. This review further explores several methods for producing bioplastics with the aim of encouraging researchers and investors to explore ways to utilize these renewable resources in order to commercialize degradable bioplastics. Challenges, future prospects and Life cycle assessment of bioplastics are also highlighted. Utilizing a variety of bioplastics obtained from renewable and cost-effective sources (e.g., organic waste, agro-industrial waste, or microalgae) and determining the pertinent end-of-life option (e.g., composting or anaerobic digestion) may lead towards the right direction that assures the sustainable production of bioplastics.

Effects of Rhizopus-arrhizus-31-Assisted Pretreatment on the Extraction and Bioactivity of Total Flavonoids from Hibiscus manihot L

The Hibiscus manihot L. (HML) Medic, an edible hibiscus of the Malvaceae family, is abundant with flavonoids. The study investigated how Rhizopus-arrhizus-31-assisted pretreatment affects the extraction and bioactivity of flavonoids from HML. The fiber structure of the fermented flavonoid sample (RFF) appears looser, more porous, and more disordered than the unfermented flavonoid sample (RUF). RFF demonstrates milder conditions and yields higher extraction rates. According to the Box-Behnken response surface optimization experiment, the optimal conditions for RFF include a material-liquid ratio of 1:41 g/mL, a 2 h extraction time, a 57% ethanol concentration, and an extraction temperature of 800 °C, resulting in a 3.69% extraction yield, which is 39.25% higher than that of RUF. Additionally, RFF exhibits greater activity than RUF in the radical-scavenging system. The IC50 values for DPPH, OH, and ABTS radicals are 83.43 μg/mL and 82.62 μg/mL, 208.38 μg/mL and 175.99 μg/mL, and 108.59 μg/mL and 75.39 μg/mL for RUF and RFF, respectively. UPLC-QTOF-MS analysis of the active components in the HML flavonoid sample revealed significant differences in the chromatograms of RUF and RFF, indicating that biofermentation led to substantial changes in composition and content from HML.

Polyhydroxyalkanoates bioproduction from bench to industry: Thirty years of development towards sustainability

The pursuit of carbon neutrality goals has sparked considerable interest in expanding bioplastics production from microbial cell factories. One prominent class of bioplastics, polyhydroxyalkanoates (PHA), is generated by specific microorganisms, serving as carbon and energy storage materials. To begin with, a native PHA producer, Cupriavidus necator (formerly Ralstonia eutropha) is extensively studied, covering essential topics such as carbon source selection, cultivation techniques, and accumulation enhancement strategies. Recently, various hosts including archaea, bacteria, cyanobacteria, yeast, and plants have been explored, stretching the limit of microbial PHA production. This review provides a comprehensive overview of current advancements in PHA bioproduction, spanning from the native to diversified cell factories. Recovery and purification techniques are discussed, and the current status of industrial applications is assessed as a critical milestone for startups. Ultimately, it concludes by addressing contemporary challenges and future prospects, offering insights into the path towards reduced carbon emissions and sustainable development goals.

Effect of oxic and anoxic conditions on intracellular storage of polyhydroxyalkanoate and polyphosphate in Magnetospirillum magneticum strain AMB-1

Magnetotactic bacteria (MTB) are microorganisms widely inhabiting the oxic-anoxic interface of aquatic environments. Beside biomineralizing magnetic nanocrystals, MTBs are able to sequester various chemical elements (e.g., carbon and phosphorus) for the biogenesis of intracellular granules, like polyhydroxyalkanoate (PHA) and polyphosphate (polyP), making them potentially important in biogeochemical cycling. Yet, the environmental controls of intracellular storage of carbon and phosphorus in MTB remain poorly understood. Here, we investigated the influence of oxic, anoxic and transient oxic-anoxic conditions on intracellular storage of PHA and polyP in Magnetospirillum magneticum strain AMB-1. In the incubations with oxygen, transmission electron microscopy revealed intercellular granules highly rich in carbon and phosphorus, which were further interpreted as PHA and polyP based on chemical and Energy-Dispersive X-ray spectroscopy analysis. Oxygen had a strong effect on PHA and polyP storage in AMB-1 cells, as PHA and polyP granules accounted for up to 47 ± 23% and 5.1 ± 1.7% of the cytoplasmic space, respectively, during continuous oxic conditions, while granules disappeared in anoxic incubations. Poly 3-hydroxybutyrate (PHB) and poly 3-hydroxyvalerate (PHV) accounted for 0.59 ± 0.66% and 0.0033 ± 0.0088% of dry cell weight, respectively, in anoxic incubations, while the values increased by a factor of 7 and 37 after oxygen was introduced. The results highlight a tight link between oxygen, carbon and phosphorus metabolisms in MTB, where favorable oxic growth conditions can lead to metabolic induction of polyP and PHA granule biogenesis.

Production of polyhydroxyalkanoates from renewable resources: a review on prospects, challenges and applications

Bioplastics replace synthetic plastics of petrochemical origin, which contributes challenge to both polymer quality and economics. Novel polyhydroxyalkanoates (PHA)-composite materials, with desirable product quality, could be developed, thus targeting the global plastics market, in the coming years. It is possible that PHA can be a greener substitute for their petroleum-based competitors since they are simply decomposed, which may lessen the pressure on municipal and industrial waste management systems. PHA production has proven to be the bottleneck in industrial application and commercialization because of the high price of carbon substrates and downstream processes required to achieve reliability. Bacterial PHA production by these municipal and industrial wastes, which act as a cheap, renewable carbon substrate, eliminates waste management hassles and acts as an efficient substitute for synthetic plastics. In the present review, challenges and opportunities related to the commercialization of polyhydroxyalkanoates are discussed and presented. Moreover, it discusses critical steps of their production process, feedstock evaluation, optimization strategies, and downstream processes. This information may provide us the complete utilization of bacterial PHA during possible applications in packaging, nutrition, medicine, and pharmaceuticals.

Polyhydroxybutyrate production by Cupriavidus necator in a corn biorefinery concept

The high costs of bioplastics' production may hinder their commercialization. Development of new processes with high yields and in biorefineries can enhance diffusion of these materials. This work evaluated the production of polyhydroxybutyrate (PHB) from the combination of milled corn starchy fraction hydrolysate and crude glycerol as substrates by the strain Cupriavidus necator LPB 1421. After optimization steps, maximum accumulation of 62 % of PHB was obtained, which represents 11.64 g.L^-1 and productivity of 0.162 g.Lh^-1. In a stirred tank bioreactor system with 8 L of operational volume, 70 % of PHB accumulation was reported, representing 14.17 g.L^-1 of the biopolymer with 0.197 g.Lh^-1 productivity. PHB recovery was conducted using a chemical digestion method, reaching >99 % purity. Therefore, the potential application of milled corn as substrate for PHB production was confirmed. The developed bioplastic process could be coupled to a bioethanol producing unit creating the opportunity of a sustainable and economic biorefinery.

Formation of polyhydroxyalkanoates using agro and industrial waste as a substrate - a review

In the present scenario, rising environmental concerns of non-biodegradable plastic pollution and depletion of petroleum based raw materials lead to the development of biopolymers. The biodegradability of biopolymers gives them a specific advantage for the environmental concerns. Polyhydroxyalkanoates (PHAs) are a type of biopolymers which are synthesized by microorganisms. Although there are different substrates available in pure forms which are currently used in the production of PHA, 40% of production cost depends on the expensive substrate which is a major disadvantage and make it far from many applications. The use of an inexpensive carbon source which is high in organic matter content such as waste streams of process industries can make this process viable and diminish PHA production cost. This study explores the current research initiatives on various agricultural and industrial waste feedstocks, formulations and processing conditions for producing PHA in a way that is both inexpensive and beneficial to the environment. The creation of fermentation conditions and metabolic engineering techniques for promoting microbial growth and PHA synthesis were also discussed in the review.

Fermentative α-Humulene Production from Homogenized Grass Clippings as a Growth Medium

Green waste, e.g., grass clippings, is currently insufficiently recycled and has untapped potential as a valuable resource. Our aim was to use juice from grass clippings as a growth medium for microorganisms. Herein, we demonstrate the production of the sesquiterpene α-humulene with the versatile organism Cupriavidus necator pKR-hum on a growth medium from grass clippings. The medium was compared with established media in terms of microbial growth and terpene production. C. necator pKR-hum shows a maximum growth rate of 0.43 h-1 in the grass medium and 0.50 h-1 in a lysogeny broth (LB) medium. With the grass medium, 2 mg/L of α-humulene were produced compared to 10 mg/L with the LB medium. By concentrating the grass medium and using a controlled bioreactor in combination with an optimized in situ product removal, comparable product concentrations could likely be achieved. To the best of our knowledge, this is the first time that juice from grass clippings has been used as a growth medium without any further additives for microbial product synthesis. This use of green waste as a material represents a new bioeconomic utilization option of waste materials and could contribute to improving the economics of grass biorefineries.

Application of the solid-state fermentation process and its variations in PHA production: a review

Solid-state fermentation (SSF) is a type of fermentation process with potential to use agro-industrial by-products as a carbon source. Nonetheless, there are few studies evaluating SSF compared to submerged fermentation (SmF) to produce polyhydroxyalkanoates (PHAs). Different methodologies are available associating the two processes. In general, the studies employ a 1st step by SSF to hydrolyze the agro-industrial by-products used as a carbon source, and a 2nd step to produce PHA that can be carried out by SmF or SSF. This paper reviewed and compared the different methodologies described in the literature to assess their potential for use in PHA production. The studies evaluated showed that highest PHA yields (86.2% and 82.3%) were achieved by associating SSF and SmF by Cupriavidus necator. Meanwhile, in methodologies using only SSF, Bacillus produced the highest yields (62% and 56.8%). Since PHA (%) does not necessarily represent a higher production by biomass, the productivity parameter was also compared between studies. We observed that the highest productivity results did not necessarily represent the highest PHA (%). C. necator presented the highest PHA yields associating SSF and SmF, however, is not the most suitable microorganism for PHA production by SSF. Concomitant use of C. necator and Bacillus is suggested for future studies in SSF. Also, it discusses the lack of studies on the association of the two fermentation methodologies, and on the scaling of SSF process for PHA production. In addition to demonstrating the need for standardization of results, for comparison between different methodologies.

Biotransformation technology and high-value application of rapeseed meal: a review

Rapeseed meal (RSM) is an agro-industrial residue of increased functional biological value that contains high-quality proteins for animal feed. Due to the presence of antinutritional factors and immature development technology, RSM is currently used as a limited feed additive and in other relatively low-value applications. With increasing emphasis on green and sustainable industrial development and the added value of agro-industrial residues, considerable attention has been directed to the removal of antinutritional factors from RSM using high-efficiency, environment-friendly, and cost-effective biotechnology. Similarly, the high-value biotransformations of RSM have been the focus of research programmes to improve utilization rate. In this review, we introduce the sources, the nutrient and antinutrient content of RSM, and emphasize improvements on RSM feed quality using biological methods and its biotransformation applications.

Production of Polyhydroxyalkanoates through Soybean Hull and Waste Glycerol Valorization: Subsequent Alkaline Pretreatment and Enzymatic Hydrolysis

Alkaline pretreatment and sequential enzymatic hydrolysis of soybean hull were investigated to obtain fermentable sugars for polyhydroxyalkanoates production along with residual glycerol as low-cost carbon sources. Soybean hull is composed of approximately 32% cellulose, 12% hemicellulose, 6% lignin, and 11% protein. Alkaline pretreatment was carried out with 2% NaOH concentration, 10% (w/v) biomass loading, and 60 min incubation time in an autoclave at 120 °C. The response surface methodology (RSM) based on the central composite design (CCD) tool was employed to optimize the enzymatic hydrolysis process, where the variables of biomass loading, enzymes’ concentration, and time were considered. The maximum total reducing sugars concentration obtained was 115.9 g∙L−1 with an enzyme concentration of 11.5 mg protein/g dry substrate for enzyme preparation B1, 2.88 mg protein/g dry substrate for XylA, and 57.6 U/g dry substrate for β-glucosidase, after 42 h at 45 °C, and pH was 4.5. Subsequently, the saccharification step was conducted by increasing the processing scale, using a 1 L tank with stirring with a controlled temperature. Implementing the same enzyme concentrations at pH 4.5, temperature of 45 °C, 260 mL working volume, and incubation time of 42 h, under fed-batch operation with substrate feeding after 14 h and 22 h, a hydrolysate with a concentration of 185.7 g∙L−1 was obtained. Initially, to verify the influence of different carbon sources on Cupriavidus necator DSMz 545 in biomass production, batch fermentations were developed, testing laboratory-grade glucose, soybean hull hydrolysate, and waste glycerol (a by-product of biodiesel processing available in large quantities) as carbon sources in one-factor-at-a-time assays, and the mixture of soybean hull hydrolysate and waste glycerol. Then, the hydrolysate and waste glycerol were consumed by C. necator, producing 12.1 g∙L−1 of biomass and achieving 39% of polyhydroxyalkanoate (PHB) accumulation. To the best of our knowledge, this is the first time that soybean hull hydrolysate has been used as a carbon source to produce polyhydroxyalkanoates, and the results suggest that this agro-industrial by-product is a viable alternative feedstock to produce value-added components.

A Two-step Strategy for High-Value-Added Utilization of Rapeseed Meal by Concurrent Improvement of Phenolic Extraction and Protein Conversion for Microbial Iturin A Production

Rapeseed meal (RSM) is a major by-product of oil extraction from rapeseed, consists mainly of proteins and phenolic compounds. The use of RSM as protein feedstock for microbial fermentation is always hampered by phenolic compounds, which have antioxidant property with health-promoting benefits but inhibit bacterial growth. However, there is still not any good process that simultaneously improve extraction efficiency of phenolic compounds with conversion efficiency of protein residue into microbial production. Here we established a two-step strategy including fungal pretreatment followed by extraction of phenolic compounds. This could not only increase extraction efficiency and antioxidant property of phenolic compounds by about 2-fold, but also improve conversion efficiency of protein residue into iturin A production by Bacillus amyloliquefaciens CX-20 by about 33%. The antioxidant and antibacterial activities of phenolic extracts were influenced by both total phenolic content and profile, while microbial feedstock value of residue was greatly improved because protein content was increased by ∼5% and phenolic content was decreased by ∼60%. Moreover, this two-step process resulted in isolating more proteins from RSM, bringing iturin A production to 1.95 g/L. In conclusion, high-value-added and graded utilization of phenolic extract and protein residue from RSM with zero waste is realized by a two-step strategy, which combines both benefits of fungal pretreatment and phenolic extraction procedures.

Integrated analysis of Whole genome sequencing and life cycle assessment for polyhydroxyalkanoates production by Cupriavidus sp. ISTL7

The current study demonstrates the enhanced production capability of strain Cupriavidus sp. ISTL7 for polyhydroxyalkanoates (PHA) using acetate and glucose (4.93 ± 0.4571 g L^-1) which was characterised analytically by GC-MS, FTIR and NMR analysis. Whole genome sequencing of strain ISTL7 unveiled an array of PHA metabolism genes which included phaA, phaB and phaC. Life cycle assessment of the protocol established that the production was most sustainable with the carbon source acetate. + Glucose as compared to acetate/glucose alone. It also concluded that solvent extraction of PHA and energy consumption during the process requires optimization to sustain the production on ecological fronts. Additionally, acetoacetyl-CoA reductase (phaB) gene was molecularly cloned, expressed and purified (27 KDa, 2.63 mg/ml). Conclusively, Cupriavidus sp. ISTL7 is a potential strain for PHA production with a scope of improvement on energy fronts which would transform the production environmentally and economically appealing.

Potential Role of Sequential Solid-State and Submerged-Liquid Fermentations in a Circular Bioeconomy

An efficient processing of organic solid residues will be pivotal in the development of the circular bioeconomy. Due to their composition, such residues comprise a great biochemical conversion potential through fermentations. Generally, the carbohydrates and proteins present in the organic wastes cannot be directly metabolized by microorganisms. Thus, before fermentation, enzymes are used in a hydrolysis step to release digestible sugars and nitrogen. Although enzymes can be efficiently produced from organic solid residues in solid-state fermentations (SsF), challenges in the development and scale-up of SsF technologies, especially bioreactors, have hindered a wider application of such systems. Therefore, most of the commercial enzymes are produced in submerged-liquid fermentations (SmF) from expensive simple sugars. Instead of independently evaluating SsF and SmF, the review covers the option of combining them in a sequential process in which, enzymes are firstly produced in SsF and then used for hydrolysis, yielding a suitable medium for SmF. The article reviews experimental work that has demonstrated the feasibility of the process and underlines the benefits that such combination has. Finally, a discussion is included which highlights that, unlike typically perceived, SsF should not be considered a counterpart of SmF but, in contrast, the main advantages of each type of fermentation are accentuated in a synergistic sequential SsF-SmF.

Biowaste-to-bioplastic (polyhydroxyalkanoates): Conversion technologies, strategies, challenges, and perspective

Biowaste management is a challenging job as it is high in nutrient content and its disposal in open may cause a serious environmental and health risk. Traditional technologies such as landfill, bio-composting, and incineration are used for biowaste management. To gain revenue from biowaste researchers around the world focusing on the integration of biowaste management with other commercial products such as volatile fatty acids (VFA), biohydrogen, and bioplastic (polyhydroxyalkanoates (PHA)), etc. PHA production from various biowastes such as lignocellulosic biomass, municipal waste, waste cooking oils, biodiesel industry waste, and syngas has been reported successfully. Various nutrient factors i.e., carbon and nitrogen source concentration and availability of dissolved oxygen are crucial factors for PHA production. This review is an attempt to summarize the recent advancements in PHA production from various biowaste, its downstream processing, and other challenges that need to overcome making bioplastic an alternate for synthetic plastic.

In vivo and Post-synthesis Strategies to Enhance the Properties of PHB-Based Materials: A Review

The transition toward "green" alternatives to petroleum-based plastics is driven by the need for "drop-in" replacement materials able to combine characteristics of existing plastics with biodegradability and renewability features. Promising alternatives are the polyhydroxyalkanoates (PHAs), microbial biodegradable polyesters produced by a wide range of microorganisms as carbon, energy, and redox storage material, displaying properties very close to fossil-fuel-derived polyolefins. Among PHAs, polyhydroxybutyrate (PHB) is by far the most well-studied polymer. PHB is a thermoplastic polyester, with very narrow processability window, due to very low resistance to thermal degradation. Since the melting temperature of PHB is around 170-180°C, the processing temperature should be at least 180-190°C. The thermal degradation of PHB at these temperatures proceeds very quickly, causing a rapid decrease in its molecular weight. Moreover, due to its high crystallinity, PHB is stiff and brittle resulting in very poor mechanical properties with low extension at break, which limits its range of application. A further limit to the effective exploitation of these polymers is related to their production costs, which is mostly affected by the costs of the starting feedstocks. Since the first identification of PHB, researchers have faced these issues, and several strategies to improve the processability and reduce brittleness of this polymer have been developed. These approaches range from the in vivo synthesis of PHA copolymers, to the enhancement of post-synthesis PHB-based material performances, thus the addition of additives and plasticizers, acting on the crystallization process as well as on polymer glass transition temperature. In addition, reactive polymer blending with other bio-based polymers represents a versatile approach to modulate polymer properties while preserving its biodegradability. This review examines the state of the art of PHA processing, shedding light on the green and cost-effective tailored strategies aimed at modulating and optimizing polymer performances. Pioneering examples in this field will be examined, and prospects and challenges for their exploitation will be presented. Furthermore, since the establishment of a PHA-based industry passes through the designing of cost-competitive production processes, this review will inspect reported examples assessing this economic aspect, examining the most recent progresses toward process sustainability.

The unconventional adverse effects of fungal pretreatment on iturin A fermentation by Bacillus amyloliquefaciens CX-20

Fungal pretreatment is the most common strategy for improving the conversion of rapeseed meal (RSM) into value-added microbial products. It was demonstrated that Bacillus amyloliquefaciens CX-20 could directly use RSM as the sole source of all nutrients except the carbon source for iturin A fermentation with high productivity. However, whether fungal pretreatment has an impact on iturin A production is still unknown. In this study, the effects of fungal pretreatment and direct bio-utilization of RSM for iturin A fermentation were comparatively analysed through screening suitable fungal species, and evaluating the relationships between iturin A production and the composition of solid fermented RSM and liquid hydrolysates. Three main unconventional adverse effects were identified. (1) Solid-state fermentation by fungi resulted in a decrease of the total nitrogen for B. amyloliquefaciens CX-20 growth and metabolism, which caused nitrogen waste from RSM. (2) The released free ammonium nitrogen in liquid hydrolysates by fungal pretreatment led to the reduction of iturin A. (3) The insoluble precipitates of hydrolysates, which were mostly ignored and wasted in previous studies, were found to have beneficial effects on producing iturin A. In conclusion, our study verifies the unconventional adverse effects of fungal pretreatment on iturin A production by B. amyloliquefaciens CX-20 compared with direct bio-utilization of RSM.

Dynamic Metabolic Analysis of Cupriavidus necator DSM545 Producing Poly(3-hydroxybutyric acid) from Glycerol

Cupriavidus necator DSM 545 can utilise glycerol to synthesise poly(3-hydroxybutyric acid) under unbalanced growth conditions, i.e., nitrogen limitation. To improve poly(3-hydroxybutyric acid) (PHB) batch production by C. necator through model-guided bioprocessing or genetic engineering, insights into the dynamic effect of the fermentation conditions on cell metabolism are crucial. In this work, we have used dynamic flux balance analysis (DFBA), a constrained-based stoichiometric modelling approach, to study the metabolic change associated with PHB synthesis during batch cultivation. The model employs the ‘minimisation of all fluxes’ as cellular objectives and measured extracellular fluxes as additional constraints. The mass balance constraints are further adjusted based on thermodynamic considerations. The resultant flux distribution profiles characterise the evolution of metabolic states due to adaptation to dynamic extracellular conditions and provide further insights towards improvements that can be implemented to enhance PHB productivity.

Rapeseed meal valorization strategies via nitrogen- and oxygen-limited production of polyhydroxyalkanoates with Pseudomonas putida

Rapeseed meal (RSM) is a candidate for biopolymer production due to its abundance, low cost and potential integration with other rapeseed-derived products. However, existing studies pursuing such schemes are limited. The feasibility of different strategies for RSM valorization via protein extraction and polyhydroxyalkanoate production were evaluated. Nitrogen-limited RSM media was produced from hydrolysis of residues which had undergone extensive protein extraction using sodium hydroxide. A study of oxygen-limited fermentation was also performed on hydrolysate of untreated RSM via batch feeding. The typical strategy of using a high carbon-to-nitrogen ratio may not be the most suitable route for polyhydroxyalkanoate (PHA) production using nitrogen-rich biomass as a feedstock. Central composite design-based experiments show that due to mass transfer limitations protein extraction at 1-L scale could only achieve yields around 50% and 69%, at room temperature and 60 °C, respectively. Protein extraction yields reduced with successive extractions, meaning that whilst the RSM hydrolysate is viable for growth, designing a valorization scheme which has the fermentation step dictated by the protein extraction may not be practical/economical. A better route which utilizes oxygen-limitation to initially induce stationary phase was identified, giving accumulation of polyhydroxyalkanoate once the oxygen levels began to recover; 8.93% and 1.75% PHA accumulation in fed-batch cultures of synthetic and RSM media, respectively. The findings demonstrate that decoupling of protein extraction performance from PHA synthesis is feasible. This study provides important insight into the degrees of freedom available in the design of a holistic valorization scheme of rapeseed meal, and high protein lignocellulosic biomass in general.

Bioconversion of Calophyllum inophyllum oilcake for intensification of rhamnolipid and polyhydroxyalkanoates co-production by Enterobacter aerogenes

The biologically derived products are highly valued due to their biodegradability, low toxicity, and renewability. However, most production processes are exorbitant due to high raw material cost and the downstream processing required for product recovery and purification. Therefore, the present study utilized the low-cost lignocellulosic biomass, Calophyllum inophyllum oilcake for the simultaneous production of PHA and rhamnolipid by a facultative anaerobe Enterobacter aerogenes. Both the products are produced during the stationary phase and constitute β- hydroxyalkanoic acids, which makes it feasible for the co-production through a single fermentation process. From the batch fermentation studies, it was revealed that the under optimum condition rhamnolipid and PHA yield are 5.81 g/L and 4.2 g/L: 5%(v/v) of inoculum size, pH of 6.5, C:N ratio of 5:1 and urea are found to be the best nitrogen source for the fermentation process. Characterization studies for extracted PHA and RL was done using- FTIR, NMR and TGA analysis.

Simultaneous hydrolysis with lipase and fermentation of rapeseed cake for iturin A production by Bacillus amyloliquefaciens CX-20

BACKGROUND

Rapeseed cake (RSC), as the intermediate by-product of oil extraction from the seeds of Brassica napus, can be converted into rapeseed meal (RSM) by solvent extraction to remove oil. However, compared with RSM, RSC has been rarely used as a raw material for microbial fermentation, although both RSC and RSM are mainly composed of proteins, carbohydrates and minerals. In this study, we investigated the feasibility of using untreated low-cost RSC as nitrogen source to produce the valuable cyclic lipopeptide antibiotic iturin A using Bacillus amyloliquefaciens CX-20 in submerged fermentation. Especially, the effect of oil in RSC on iturin A production and the possibility of using lipases to improve the iturin A production were analyzed in batch fermentation.

RESULTS

The maximum production of iturin A was 0.82 g/L at the optimal initial RSC and glucose concentrations of 90 and 60 g/L, respectively. When RSC was substituted with RSM as nitrogen source based on equal protein content, the final concentration of iturin A was improved to 0.95 g/L. The production of iturin A was further increased by the addition of different lipase concentrations from 0.1 to 5 U/mL into the RSC medium for simultaneous hydrolysis and fermentation. At the optimal lipase concentration of 0.5 U/mL, the maximal production of iturin A reached 1.14 g/L, which was 38.15% higher than that without any lipase supplement. Although rapeseed oil and lipase were firstly shown to have negative effects on iturin A production, and the effect would be greater if the concentration of either was increased, their respective negative effects were reduced when used together.

CONCLUSIONS

Appropriate relative concentrations of lipase and rapeseed oil were demonstrated to support optimal iturin A production. And simultaneous hydrolysis with lipase and fermentation was an effective way to produce iturin A from RSC using B. amyloliquefaciens CX-20.

Establishment of a rapeseed meal fermentation model for iturin A production by Bacillus amyloliquefaciens CX-20

Iturin A is an important broad-spectrum antifungal cyclic lipopeptide used as an ideal potential biological control agent. However, its application is limited mainly due to the producer strains' low productivity and the high production costs. Here, a potentially industrial strain Bacillus amyloliquefaciens CX-20 was proved to use low-cost rapeseed meal (RSM) as the sole source of all nutrients except the carbon source for the high productivity of iturin A. A fermentation model was first established to analyse the specific roles of different RSM components on iturin A production. Proteins and minerals in RSM were confirmed to play positive role, whereas fibre had negative effect. And the maximal concentration of iturin A was predicted to be more than 1.64 g l-1 by the established evaluation model. Moreover, submerged fermentation of B. amyloliquefaciens CX-20 demonstrated a strong ability to hydrolyse RSM and release water-soluble nutrients. This fermentation broth, a mixture of Bacillus, iturin A and RSM hydrolysate, could simultaneously combat clubroot disease and promote the growth of Brassica napus. In conclusion, this study provides a promising strategy to achieve full utilization of RSM for the production of a combination of value-added biological control agent and biofertilizer.

Modeling the bioconversion of starch to P(HB-co-HV) optimized by experimental design using Bacillus megaterium BBST4 strain

Poly(hydroxybutyrate-co-hydroxyvalerate) (P(HB-co-HV)) is a prominent biopolymer as a potential candidate for use in the biomedical area. Several Bacillus spp. strains show promising characteristics in the use of several carbon sources and are an interesting alternative for the production of P(HB-co-HV). Sewage from the agricultural and food processing industries can be used to obtain abundantly starch as a carbon source for PHA production. The aim of the present study was to optimize by response surface methodology and desirability, the production of PHA by a Bacillus megaterium strain using starch as the sole carbon source. Two optimal conditions were determined without sporulation and were used to perform new experiments to calibrate and validate a mechanistic model, developed to simulate the dynamics of PHA and biomass production. The developed model successfully represents the kinetics of the microorganism. Employing different characterization techniques, it was determined that the PHA produced by the strain is a copolymer composed of different HB:HV proportions. Using starch as the sole carbon source in a minimal salt medium, this work shows the first reports in the literature of: 1) a mathematical model for predicting growth kinetic and PHA production for B. megaterium strain and 2) a Bacillus spp. producing P(HB-co-HV) copolymer.

Valorization of crude glycerol based on biological processes for accumulation of lipophilic compounds

Bacteria that are capable of accumulating lipids in their cells as storage compounds can also produce polyhydroxyalkanoates of high technological value, depending on the specific culture conditions. The objective of this study was to utilize crude glycerol from biodiesel (CGB) as a substrate, which is a major byproduct from biodiesel production, to produce lipophilic compounds. Bacillus megaterium INCQS 425 was cultivated and evaluated for the production of lipophilic compounds and the properties of these compounds were investigated. Cultivation of the bacteria in a medium with a C:N ratio of 0.60:1 favored the accumulation of lipids by (17.5%) comprising mainly palmitic acid (13.08%), palmitoleic (39.48%), and especially oleic acid (37.02%), which imparts good characteristics to biodiesel. Meanwhile, cultivation of the bacteria in a medium with a C:N ratio of 4:1 favored the accumulation of polyhydroxyalkanoates (PHA) (3.31gL^-1) mainly comprising medium and long chain PHA. Low crystallinity (<30%) and excellent thermal properties make them suitable for processes that demand high temperatures, such as extrusion. The lipids produced in the present study had satisfactory oxidative stability for the production of quality biodiesel. The polyhydroxyalkanoates produced in the study are of low cost and have promising thermal properties that justify its technological potential, thereby configuring highly competitive bioproducts.

Polyhydroxyalkanoate synthesis based on glycerol and implementation of the process under conditions of pilot production

The present study addresses the synthesis and properties of polyhydroxyalkanoates (PHA) of different composition synthesized by Cupriavidus eutrophus B-10646 using glycerol as a carbon substrate. Poly(3-hydroxybutyrate) [P(3HB)] was effectively synthesized in fed-batch culture in a 30-L fermenter on glycerol of various purification degrees, with 99.5, 99.7, and 82.1% content of the main component. Purified glycerol (99.7%) was used for 150-L pilot scale fermentation. The total biomass and P(3HB) concentration reached 110 and 85.8 g/L, respectively, after 45 h of fed-batch fermentation. An average volumetric productivity of P(3HB) was 1.83 g/(L h). The degree of crystallinity and molecular weight of P(3HB) synthesized on glycerol were lower than and temperature characteristics were the same as those of P(3HB) synthesized on sugars.

Valorization of waste glycerol for the production of poly (3-hydroxybutyrate) and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by Cupriavidus necator and extraction in a sustainable manner

Glycerol is a by-product of many industrial processes and huge amounts of it are generated in the form of waste, thereby necessitating a search for the method of its disposal. An interesting solution is the valorization of crude glycerol into value added product such as polyhydroxyalkanoates (PHAs). The feasibility of producing PHAs by Cupriavidus necator was evaluated using crude glycerol (WG). Various cultivation strategies were designed for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by adding different organic acids as precursors at different concentrations levels. Batch cultivation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production showed accumulation of 6.76g/L biomass containing 4.84g/L copolymer on WG with a maximum 3-hydroxyvalerate content of 24.6mol%. PHAs extraction using a non-toxic and recyclable solvent, 1,2 propylene carbonate, showed the highest recovery yield (90%) and purity (93%) at 120°C temperature and 30min incubation. This is the first report on jatropha based glycerol valorization for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production coupled with extraction using non-toxic solvent.

Produção de poli(3-hidroxibutirato) por Cupriavidus necator em batelada alimentada usando glicerol

Resumo Poli(3-hidroxibutirato) [P(3HB)] é um poliéster natural, biodegradável e é considerado um substituto atrativo para polímeros petroquímicos, pois tem a vantagem de ser degradado em solo dentro de alguns meses por micro-organismos. Este trabalho explora três estratégias para sintetizar P(3HB) a partir de Cupriavidus necator tendo glicerol como cosubstrato: cultivo sem glicerol, com adição de 20 g L–1 de glicerol na fase de produção do polímero e 20 g L–1 de glicerol no início do cultivo, a fim de avaliar o seu efeito sobre o crescimento celular e a síntese do polímero. Os resultados mostraram que a adição de glicerol no início do cultivo conduziu a maiores valores de percentagem de acúmulo de P(3HB) (64,12%). No entanto, nos experimentos sem glicerol podem ser observados maiores valores para fator de conversão em substrato (0,17 g g–1). Esses parâmetros apresentaram diferenças estatisticamente significativas em função da estratégia de cultivo utilizado.

Microbial Cometabolism and Polyhydroxyalkanoate Co-polymers

Polyhydroxyalkanoate (PHAs) are natural, biodegradable biopolymers, which can be produced from renewable materials. PHAs have potential to replace petroleum derived plastics. Quite a few bacteria can produce PHA under nutritional stress. They generally produce homopolymers of butyrate i.e., polyhydroxybutyrate (PHB), as a storage material. The biochemical characteristics of PHB such as brittleness, low strength, low elasticity, etc. make these unsuitable for commercial applications. Co-polymers of PHA, have high commercial value as they overcome the limitations of PHBs. Co-polymers can be produced by supplementing the feed with volatile fatty acids or through hydrolysates of different biowastes. In this review, we have listed the potential bacterial candidates and the substrates, which can be co-metabolized to produce PHA co-polymers.

Microbial production of polyhydroxyalkanoates (PHAs) and its copolymers: A review of recent advancements

Traditional mineral oil based plastics are important commodity to enhance the comfort and quality of life but the accumulation of these plastics in the environment has become a major universal problem due to their low biodegradation. Solution to the plastic waste management includes incineration, recycling and landfill disposal methods. These processes are very time consuming and expensive. Biopolymers are important alternatives to the petroleum-based plastics due to environment friendly manufacturing processes, biodegradability and biocompatibility. Therefore use of novel biopolymers, such as polylactide, polysaccharides, aliphatic polyesters and polyhydroxyalkanoates is of interest. PHAs are biodegradable polyesters of hydroxyalkanoates (HA) produced from renewable resources by using microorganisms as intracellular carbon and energy storage compounds. Even though PHAs are promising candidate for biodegradable polymers, however, the production cost limit their application on an industrial scale. This article provides an overview of various substrates, microorganisms for the economical production of PHAs and its copolymers. Recent advances in PHAs to reduce the cost and to improve the performance of PHAs have also been discussed.

Medium chain length polyhydroxyalkanoates consisting primarily of unsaturated 3-hydroxy-5-cis-dodecanoate synthesized by newly isolated bacteria using crude glycerol

Background

Our study aimed to search for novel bacteria capable of producing polyhydroxyalkanoates (PHAs) using crude glycerol residue obtained from biodiesel production in which used cooking oils were the substrates.

Results

Newly isolated bacteria from soils in Thailand were screened for the efficient production of PHAs from crude glycerol. The bacterial strains were cultivated on glucose, refined glycerol, crude glycerol, or various cooking oils (canola oil, palm oil, soybean oil, sunflower oil, corn oil, grape seed oil, olive oil, rice bran oil, camellia seed oil) for growth and PHA production. The effects of the total organic carbon (TOC) concentration and the mole ratio of carbon to nitrogen were investigated in batch cultivation. ¹H NMR, two dimensional-¹H-correlation spectroscopy (2D-¹H-COSY) and ¹³C NMR analyses confirmed four bacterial strains were capable of producing medium-chain-length PHAs (mcl-PHAs), consisting of 3-hydroxyoctanoate (3HO) and 3-hydroxy-5-cis-dodecanoate (3H5DD), from crude glycerol. On the basis of phenotypic features and genotypic investigations, the bacterial strains were assigned as: ASC1, Acinetobacter genus (94.9 % similarity); ASC2, Pseudomonas genus (99.2 % similarity); ASC3, Enterobacter genus (99.2 % similarity); ASC4, Bacillus genus (98.4 % similarity). The highest amount of mcl-PHAs, 17.5 ± 0.8 g/L (content 61.8 ± 3.3 % wt), with 3HO (14.7 ± 2.2 mol %), 3H5DD (85.3 ± 2.2 mol %), and a total biomass of 32.3 ± 0.3 g/L, was obtained from Pseudomonas sp. ASC2 in batch cultivation after 36 h. The mcl-PHAs recovered had a number-average molecular weight (M_N) of 3.6 × 10⁴ Da. Homopolymeric 3H5DD was obtained when the cultivation time was prolonged to 96 h.

Conclusions

Novel PHA-producing strains were isolated and identified. These bacterial strains are able to produce mcl-PHAs from crude glycerol. The mcl-PHAs produced contained a high percentage of 3H5DD, which suggests their future application as softeners mixed with other biomaterials. The unsaturated side chain of 3H5DD monomers containing double bounds offers additional potential for improving the properties of the mcl-PHAs or extending their applications to the food industry.

Effective production of low crystallinity Poly(3-hydroxybutyrate) by recombinant E. coli strain JM109 using crude glycerol as sole carbon source

Utilization of bio-diesel by-products (glycerol) for microbial polymer production has created a novel biorefinery concept. In the present study, recombinant Escherichia coli JM109 was used for the production of P(3 HB) from glycerol as carbon source. Batch fermentation in a 7.5L bioreactor with the statistically optimized culture condition (pre-treated glycerol: 27.5 g/L and casein hydrolysate: 5.25 g/L) scaled up the P3HB production to 65% (∼ 8 g/L). FTIR, (1)H and (13)C NMR analysis proved the polymer produced to be P(3 HB). Gel permeation chromatography, Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) demonstrated the produced P(3 HB) to have high molecular weight (2.84 × 10(6)) and lowered crystallinity (∼ 30%) compared to commercial polymer. Integrating the production efficiency and the thermal characteristics of the polymer produced by recombinant E. coli, the viability and sustainability of biofuels and biopolymers for economic human need could be enhanced.

Engineering the heterotrophic carbon sources utilization range of Ralstonia eutropha H16 for applications in biotechnology

Ralstonia eutropha H16 is an interesting candidate for the biotechnological production of polyesters consisting of hydroxy- and mercaptoalkanoates, and other compounds. It provides all the necessary characteristics, which are required for a biotechnological production strain. Due to its metabolic versatility, it can convert a broad range of renewable heterotrophic resources into diverse valuable compounds. High cell density fermentations of the non-pathogenic R. eutropha can be easily performed. Furthermore, this bacterium is accessible to engineering of its metabolism by genetic approaches having available a large repertoire of genetic tools. Since the complete genome sequence of R. eutropha H16 has become available, a variety of transcriptome, proteome and metabolome studies provided valuable data elucidating its complex metabolism and allowing a systematic biology approach. However, high production costs for bacterial large-scale production of biomass and biotechnologically valuable products are still an economic challenge. The application of inexpensive raw materials could significantly reduce the expenses. Therefore, the conversion of diverse substrates to polyhydroxyalkanoates by R. eutropha was steadily improved by optimization of cultivation conditions, mutagenesis and metabolic engineering. Industrial by-products and residual compounds like glycerol, and substrates containing high carbon content per weight like palm, soybean, corn oils as well as raw sugar-rich materials like molasses, starch and lignocellulose, are the most promising renewable substrates and were intensively studied.

Synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) from unrelated carbon sources in engineered Rhodospirillum rubrum

Different genes encoding pyridine nucleotide transhydrogenases (pntAB, udhA) and acetoacetyl-CoA reductases (phaB) were heterologously overexpressed in Rhodospirillum rubrum S1. A recombinant strain, which harbored the gene encoding the membrane-bound transhydrogenase PntAB from Escherichia coli MG1655 and the phaB1 gene coding for an NADPH-dependent acetoacetyl-CoA reductase from Ralstonia eutropha H16, accumulated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [Poly(3HB-co-3HV)] with a 3HV fraction of up to 13 mol% from fructose. This was a 13-fold increase of the 3HV content when compared to the wild-type strain. Higher contents of 3HV are known to reduce the brittleness of this polymer, which is advantageous for most applications. The engineered R. rubrum strain was also able to synthesize this industrially relevant copolymer from CO2 and CO from artificial synthesis gas (syngas) with a 3HV content of 56 mol%. The increased incorporation of 3HV was attributed to an excess of propionyl-CoA, which was generated from threonine and related amino acids to compensate for the intracellular redox imbalance resulting from the transhydrogenase reaction. Thereby, our study presents a novel, molecular approach to alter the composition of bacterial PHAs independently from external precursor supply. Moreover, this study also provides a promising production strain for syngas-derived second-generation biopolymers.

Sunflower-based biorefinery: poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from crude glycerol, sunflower meal and levulinic acid

Polyhydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] production was developed in bioreactor cultures using the strain Cupriavidus necator DSM 7237 cultivated on crude glycerol, sunflower meal (SFM) hydrolysates and levulinic acid as the sole fermentation feedstocks. Bacterial growth and PHB production was influenced significantly by the free amino nitrogen and inorganic phosphorus content of the SFM hydrolysate. Fed-batch bioreactor fermentations led to the production of 27gL(-1) PHB with an intracellular content of 72.9% (w/w). Continuous feeding of levulinic acid led to the production of up to 23.4gL(-1) P(3HB-co-3HV) with an intracellular content of 66.4% (w/w) and a 3HV content of 22.5mol%. A maximum 3HV content of 31mol% was achieved at earlier fermentation time (53h). Thus, levulinic acid could be combined with biodiesel industry by-products for the production of high P(3HB-co-3HV) concentration, intracellular content and industrially useful 3HV content.

Biohydrogen and polyhydroxyalkanoate co-production by Enterobacter aerogenes and Rhodobacter sphaeroides from Calophyllum inophyllum oil cake

The feasibility of coupled biohydrogen and polyhydroxyalkanoate production by Enterobacter aerogenes and Rhodobacter sphaeroides using Calophyllum inophyllum oil cake was studied under dark and photo fermentation conditions. The utilization of a non-edible acidic oil cake (C. inophyllum), and exploitation of a modified minimal salt media led to reduction in the cost of media. Cost of fermentation is reduced by implementation of alternate dark-photo fermentative periods and through the use of a co-culture consisting of a dark fermentative (E. aerogenes) and a photo fermentative (R. sphaeroides) bacterium. The biohydrogen and polyhydroxyalkanoate produced were 7.95 L H2/L media and 10.73 g/L media, respectively, under alternate dark and photo fermentation and were 3.23 L H2/L media and 5.6g/L media, respectively under complete dark fermentation. The characteristics of the oil cake and alternate dark (16 h) and photo (8h) fermentative conditions were found to be supportive in producing high biohydrogen and polyhydroxyalkanoate (PHA) yield.