Production of medical-grade biopolymer in air lift bioreactors

Microbes are known to produce biopolymers for societal applications. Economical production of biopolymer (PHB) is desperately required to significantly replace or reduce usage of non-degradable polypropylene produced by disappearing petroleum resources. Besides it is also equally important to ensure abundant availability of low cost medical grade biopolymers which can be used for several medical applications in society. It has been invariably observed that mechanical agitation in the bioreactors features major power consumption in the operation of bioreactors therefore usage of air lift bioreactors are likely to reduce power consumption by mechanical agitation significantly thereby leading to economic biopolymer production. Present investigation evaluates the possible role of pneumatic bioreactors (e.g., Bubble Column, Outer Aeration Inner Settling, Inner Aeration Outer Settling) as alternates to mechanically agitated bioreactors for the economic production of medical grade biopolymers P(3HB) by Bacillus thuringiensis IAM12077 using glycerol and glucose as major substrates. It was observed that Bacillus thuringiensis IAM12077 cultivations featured Biopolymer P(3HB) accumulations of 22.48%, 37.07%, 27.73%, in BC, OAIS, IAOS air lift bioreactors. Relatively higher product yield, volumetric productivity and P(3HB) accumulation was observed in Outer Aeration Inner Settling (OAIS) air lift bioreactor configuration as opposed to other pneumatic bioreactors.

Synthetic biology strategies for sustainable bioplastic production by yeasts

The increasing environmental concerns regarding conventional plastics have led to a growing demand for sustainable alternatives, such as biodegradable plastics. Yeast cell factories, specifically Saccharomyces cerevisiae and Yarrowia lipolytica, have emerged as promising platforms for bioplastic production due to their scalability, robustness, and ease of manipulation. This review highlights synthetic biology approaches aimed at developing yeast cell factories to produce key biodegradable plastics, including polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and poly (butylene adipate-co-terephthalate) (PBAT). We explore recent advancements in engineered yeast strains that utilize various synthetic biology strategies, such as the incorporation of new genetic elements at the gene, pathway, and cellular system levels. The combined efforts of metabolic engineering, protein engineering, and adaptive evolution have enhanced strain efficiency and maximized product yields. Additionally, this review addresses the importance of integrating computational tools and machine learning into the Design-Build-Test-Learn cycle for strain development. This integration aims to facilitate strain development while minimizing effort and maximizing performance. However, challenges remain in improving strain robustness and scaling up industrial production processes. By combining advanced synthetic biology techniques with computational approaches, yeast cell factories hold significant potential for the sustainable and scalable production of bioplastics, thus contributing to a greener bioeconomy.

Metabolic conversion of phenol to polyhydroxyalkanoate (PHA) for addressing dual environmental challenges: A review

A sustainable approach to microbial polyhydroxyalkanoate (PHA) production involves utilizing waste as a substrate, which can include toxic pollutants like phenol as a carbon feedstock. Phenol-contaminated effluents offer cost-effective and readily available resources for PHA production, while simultaneously addressing phenol contamination issues. Understanding the metabolic conversion of phenol to PHA is crucial to enhance its efficiency, especially considering phenol's toxicity to microbial cells and the substrate-dependent nature of microbial PHA production. In this review, the mechanisms of phenol biodegradation and PHA biosynthesis are first independently elucidated to comprehend the role of bacteria in these processes. Phenol can be metabolized aerobically via various pathways, including catechol meta-cleavage I and II, catechol ortho-cleavage, protocatechuate ortho-cleavage, and protocatechuate meta-cleavage, as well as anaerobically via 4-hydrozybenzoate and/or n-caproate formation. Meanwhile, PHA can be synthesized through the acetoacetyl-CoA (pathway I), de novo fatty acids synthesis (pathway II), β-oxidation (pathway III), and the tricarboxylic acid (TCA) cycle, with the induction of these pathways are highly dependent on the substrate. Given that the link between these two mechanisms was not comprehensively reported before, the second part of the review delve into understanding phenol conversion into PHA, specifically polyhydroxybutyrate (PHB). While phenol toxicity can inhibit bacterial performance, it can be alleviated through the utilization of microbial mixed culture (MMC), which offers a wider range of metabolic capabilities. Utilizing phenol as a carbon feedstock for PHB accumulation could offer a viable approach to boost PHA's commercialization while addressing the issue of phenol pollution.

Elucidating regulation of polyhydroxyalkanoate metabolism in Ralstonia eutropha: Identification of transcriptional regulators from phasin and depolymerase genes

Despite the ever-growing research interest in polyhydroxyalkanoates (PHAs) as green plastic alternatives, our understanding of the regulatory mechanisms governing PHA synthesis, storage, and degradation in the model organism Ralstonia eutropha remains limited. Given its importance for central carbon metabolism, PHA homeostasis is probably controlled by a complex network of transcriptional regulators. Understanding this fine-tuning is the key for developing improved PHA production strains thereby boosting the application of PHAs. We conducted promoter pull-down assays with crude protein extracts from R. eutropha Re2058/pCB113, followed by liquid chromatography with tandem mass spectrometry, to identify putative transcriptional regulators involved in the expression control of PHA metabolism, specifically targeting phasin phaP1 and depolymerase phaZ3 and phaZ5 genes. The impact on promoter activity was studied in vivo using β-galactosidase assays and the most promising candidates were heterologously produced in Escherichia coli, and their interaction with the promoters investigated in vitro by electrophoretic mobility shift assays. We could show that R. eutropha DNA-binding xenobiotic response element-family-like protein H16_B1672, specifically binds the phaP1 promoter in vitro with a KD of 175 nM and represses gene expression from this promoter in vivo. Protein H16_B1672 also showed interaction with both depolymerase promoters in vivo and in vitro suggesting a broader role in the regulation of PHA metabolism. Furthermore, in vivo assays revealed that the H-NS-like DNA-binding protein H16_B0227 and the peptidyl-prolyl cis-trans isomerase PpiB, strongly repress gene expression from PphaP1 and PphaZ3, respectively. In summary, this study provides new insights into the regulation of PHA metabolism in R. eutropha, uncovering specific interactions of novel transcriptional regulators.

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.

Systematizing Microbial Bioplastic Production for Developing Sustainable Bioeconomy: Metabolic Nexus Modeling, Economic and Environmental Technologies Assessment

The excessive usage of non-renewable resources to produce plastic commodities has incongruously influenced the environment's health. Especially in the times of COVID-19, the need for plastic-based health products has increased predominantly. Given the rise in global warming and greenhouse gas emissions, the lifecycle of plastic has been established to contribute to it significantly. Bioplastics such as polyhydroxy alkanoates, polylactic acid, etc. derived from renewable energy origin have been a magnificent alternative to conventional plastics and reconnoitered exclusively for combating the environmental footprint of petrochemical plastic. However, the economically reasonable and environmentally friendly procedure of microbial bioplastic production has been a hard nut to crack due to less scouted and inefficient process optimization and downstream processing methodologies. Thereby, meticulous employment of computational tools such as genome-scale metabolic modeling and flux balance analysis has been practiced in recent times to understand the effect of genomic and environmental perturbations on the phenotype of the microorganism. In-silico results not only aid us in determining the biorefinery abilities of the model microorganism but also curb our reliance on equipment, raw materials, and capital investment for optimizing the best conditions. Additionally, to accomplish sustainable large-scale production of microbial bioplastic in a circular bioeconomy, extraction, and refinement of bioplastic needs to be investigated extensively by practicing techno-economic analysis and life cycle assessment. This review put forth state-of-the-art know-how on the proficiency of these computational techniques in laying the foundation of an efficient bioplastic manufacturing blueprint, chiefly focusing on microbial polyhydroxy alkanoates (PHA) production and its efficacy in outplacing fossil based plastic products.

Flow cytometry: a tool for understanding the behaviour of polyhydroxyalkanoate accumulators

The use of mixed microbial cultures (MMCs) is seen as an attractive strategy for polyhydroxyalkanoate (PHA) production. In order to optimize the MMC-PHA production process, tools are required to improve our understanding of the physiological state of the PHA-storing microorganisms within the MMC. In the present study, we explored the use of flow cytometry to analyse the metabolic state and polyhydroxybutyrate (PHB) content of the microorganisms from an MMC-PHA production process. A sequencing batch reactor under a feast and famine regime was used to enrich an MMC with PHB-storing microorganisms. Interestingly, once the PHB-storing microorganisms are selected, the level of PHB accumulation depends largely on the metabolic state of these microorganisms and not exclusively on the consortium composition. These results demonstrate that flow cytometry is a powerful tool to help to understand the PHA storage response of an MMC-PHA production process. KEY POINTS: • Flow cytometry allows to measure PHB content and metabolic activity over time. • Microorganisms showing high PHB content also have high metabolic activity. • PHB producers with low metabolic activity show low PHB content.

Paraburkholderia tagetis sp. nov., a novel species isolated from roots of Tagetes patula enhances the growth and yield of Solanum lycopersicum L. (tomato)

A multifunctional, Gram-stain-negative, aerobic, motile by flagella, short-rod shaped bacteria, designated strain RG36^T was isolated from roots of marigold plant (Tagetes patula) sampled at Dongguk University, Republic of Korea. A 16S rRNA sequences indicated that the closest phylogenetic neighbors were Paraburkholderia acidiphila 7Q-K02^T (99.0%) and Paraburkholderia sacchari IPT101^T (98.9%) of the family Burkholderiaceae. The draft genome size was 8.52 Mb (63.7% GC). The genome contained 7,381 coding sequences. Digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) values of strain RG36^T with its most closely related species were only 83.1-88.7 and 27.6-36.7%, respectively. Strain RG36^T contained Q-8 as the major respiratory quinone and its main fatty acids (>10%) were C_16:0, C_17:0 cyclo, C_19:0 cyclo ω8c, and summed feature 8 (comprising C_18:1 ω7c and/or C_18:1 ω6c). Strain RG36^T accumulates polyhydroxybutyrates (PHB) and exhibits multiple plant growth-promoting properties including production of indole-3-acetic acid (IAA), siderophores, protease, phosphate solubilization, and harboring gene clusters for its multifunctional properties. A pot experiment was conducted to evaluate the effect of PGPR on the growth of Solanum lycopersicum L. (Tomato). Result also confirmed the ability of strain RG36^T to promote tomato plant growth, especially it increases the yield of tomatoes. Structural assessment of the bioplastic by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and GC-MS spectroscopy, which confirmed the structure of the polymer as PHB. Our study revealed the potential of strain RG36^T to promote the growth of tomato plant and fruit yield by stimulating the various phytohormones, which could be use as bio-fertilizers to reduce the use of chemical fertilizers and promotes sustainable agricultural production. The phenotypic, chemotaxonomic and phylogenetic data, and genome analysis showed that strain RG36^T represents a novel species of the genus Paraburkholderia, for which the name Paraburkholderia tagetis sp. nov. is proposed. The type strain is RG36^T (=KACC 22685^T = TBRC 15696^T).

Initial pH Conditions Shape the Microbial Community Structure of Sewage Sludge in Batch Fermentations for the Improvement of Volatile Fatty Acid Production

Conversion of wastewater treatment plants into biorefineries is a sustainable alternative for obtaining valuable compounds, thus reducing pollutants and costs and protecting the environment and human health. Under specific operating conditions, microbial fermentative products of sewage sludge are volatile fatty acids (VFA) that can be precursors of polyhydroxyalkanoate thermoplastic polyesters. The role of various operating parameters in VFA production has yet to be elucidated. This study aimed to correlate the levels of VFA yields with prokaryotic microbiota structures of sewage sludge in two sets of batch fermentations with an initial pH of 8 and 10. The sewage sludge used to inoculate the batch fermentations was collected from a Sicilian WWTP located in Marineo (Italy) as a case study. Gas chromatography analysis revealed that initial pH 10 stimulated chemical oxygen demands (sCOD) and VFA yields (2020 mg COD/L) in comparison with initial pH 8. Characterization of the sewage sludge prokaryotic community structures—analyzed by next-generation sequencing of 16S rRNA gene amplicons—demonstrated that the improved yield of VFA paralleled the increased abundance of fermenting bacteria belonging to Proteobacteria, Bacteroidetes, Chloroflexi, and Firmicutes phyla and, conversely, the reduced abundance of VFA-degrading strains, such as archaeal methanogens.

Algal bioplastics: current market trends and technical aspects

Abstract

Plastics are undebatably a hot topic of discussion across international forums due to their huge ecological footprint. The onset of COVID-19 pandemic has exacerbated the issue in an irreversible manner. Bioplastics produced from renewable sources are a result of lookout for sustainable alternatives. Replacing a ton of synthetic plastics with biobased ones reduces 1.8 tons CO2 emissions. Here, we begin with highlighting the problem statement-Plastic accumulation and its associated negative impacts. Microalgae outperforms plants and microbes, when used to produce bioplastic due to superior growth rate, non-competitive nature to food, and simultaneous wastewater remediation. They have minimal nutrient requirements and less dependency on climatic conditions for cultivation. These are the reasons for current boom in the algal bioplastic market. However, it is still not at par in price with the petroleum-based plastics. A brief market research has been done to better evaluate the current global status and future scope of algal bioplastics. The objective of this review is to propose possible solutions to resolve the challenges in scale up of bioplastic industry. Various bioplastic production technologies have been comprehensively discussed along with their optimization strategies. Overall studies discussed show that in order to make it cost competitive adopting a multi-dimensional approach like algal biorefinery is the best way out. A holistic comparison of any bio-based alternative with its conventional counterpart is imperative to assess its impact upon commercialization. Therefore, the review concludes with the life cycle assessment of bioplastics and measures to improve their inclusivity in a circular economy.

Graphical Abstract

Aislamiento y caracterización de bacterias productoras de biopolimeros a partir de efluentes industriales

Se realizó una caracterización físico-química de los efluentes procedentes de industrias del sector educación, metalmecánico, lácteos y confitería de la ciudad de Manizales, Caldas; posteriormente se obtuvieron aislamientos, en medios diferenciales suplementados, de bacterias con potencial para la producción de biopolímeros a los cuales se les aplicó pruebas para la caracterización morfológica, bioquímica y molecular. Los parámetros físico químicos obtenidos de los efluentes industriales demuestran diferencias entre ellos, ya que cada industria genera diferentes residuos aportando una determinada contaminación al efluente, se obtuvieron 73 aislamientos productores de exopolisacáridos (EPS) y 101 productores de polihidroxialcanoatos (PHA), con características morfológicas y bioquímicas variables. El estudio muestra que los efluentes industriales son una gran fuente de bacterias de interés para la producción de diversos polímeros microbianos; principalmente aquellos que producen polímeros tipo biopoliésteres intracelulares como PHA, debido a su variabilidad físico-química y nutricional permitiendo que los microorganismos se adapten a diversas características medioambientales y de composición.

Finding of novel polyhydroxybutyrate producer Loktanella sp. SM43 capable of balanced utilization of glucose and xylose from lignocellulosic biomass

Polyhydroxybutyrate (PHB) is a potential substitute for plastics derived from fossil fuels, owing to its biodegradable and biocompatible properties. Lignocellulosic biomass could be used to reduce PHB production costs; however, the co-utilization of sugars, such as glucose and xylose, without catabolite repression is a difficult problem to be solved. Here, we selected a novel Loktanella sp. SM43 from a marine environment and optimized the conditions for PHB production. Loktanella sp. SM43 showed high PHB production (66.5% content) from glucose. When glucose and xylose were used together, this strain showed high utilization of both substrates compared to other high PHB-producers such as Halomonas sp. and Cupriavidus necator, which showed glucose preference. Loktanella sp. SM43 showed high growth and PHB production with lignocellulosic hydrolysates. When pine tree hydrolysates were used, PHB production was the highest at 3.66 ± 0.01 g/L, followed by Miscanthus (3.46 ± 0.09 g/L) and barley straw hydrolysate (3.36 ± 0.36 g/L). Overall, these results reveal the potential of Loktanella sp. SM43 to produce PHB using various lignocellulosic hydrolysates as feedstock and the first systematic study for PHB production with Loktanella sp. The approach of screening novel strains is a strategy to overcome co-utilization of sugars without genetic engineering.

Polyhydroxyalkanoates, the bioplastics of microbial origin: Properties, biochemical synthesis, and their applications

The rising plastic pollution deteriorates the environment significantly as these petroleum-based plastics are not biodegradable, and their production requires natural fuels (energy source) and other resources. Polyhydroxyalkanoates (PHAs) are bioplastic and a sustainable and eco-friendly alternative to synthetic plastics. PHAs can be entirely synthesized using various microorganisms such as bacteria, algae, and fungi. These value-added biopolymers show promising properties such as enhanced biodegradability, biocompatibility, and other chemo-mechanical properties. Further, it has been established that the properties of PHA polymers depend on the substrates and chemical composition (monomer unit) of these polymers. PHAs hold great potential as an alternative to petroleum-based polymers, and further research for economic production and utilization of these biopolymers is required. The review describes the synthesis mechanism and different properties of microbially synthesized PHAs for various applications. The classification of PHAs and the multiple techniques necessary for their detection and evaluation have been discussed. In addition, the synthesis mechanism involving the genetic regulation of these biopolymers in various microbial groups has been described. This review provides information on various commercially available PHAs and their application in multiple sectors. The industrial production of these microbially synthesized polymers and the different extraction methods have been reviewed in detail. Furthermore, the review provides an insight into the potential applications of this biopolymer in environmental, industrial, and biomedical applications.

Microbial conversion of lignin rich biomass hydrolysates to medium chain length polyhydroxyalkanoates (mcl-PHA) using Pseudomonas putida KT2440

As world moves toward increasing number of products being produced from renewable lignocellulosic agricultural and forest residues, the major classes of products that will shift to greener routes on priority are energy, fuels, and materials in that order. In materials segment, polyhydroxyalkanoates are an emerging class of biopolyesters with several potential industrial uses. The present work investigates medium chain length polyhydroxyalkanoates (mcl-PHA) producing capabilities of Pseudomonas putida KT2440 from a mixture of compounds produced from lignocellulosic biomass deconstruction. The hydrolysates obtained from nitric acid pretreatment of lignin rich cotton stalk (CS) and palm empty fruit bunch (EFB) were used as substrates for production of mcl-PHA. Presence of 3-hydroxydecanoate and 3-hydroxyocytanoate observed on GC-MS confirmed PHA accumulation in the cells. PHA accumulation was estimated between 20% and 35% of cell dry weight when grown on both model substrates as well as biomass hydrolysates. PHA titers obtained on hydrolysates of CS and EFB were 0.24 g/L and 0.21 g/L, respectively.

Synthetic Control of Metabolic States in Pseudomonas putida by Tuning Polyhydroxyalkanoate Cycle

Polyhydroxyalkanoates (PHAs) are polyesters produced by numerous microorganisms for energy and carbon storage. Simultaneous synthesis and degradation of PHA drives a dynamic cycle linked to the central carbon metabolism, which modulates numerous and diverse bacterial processes, such as stress endurance, pathogenesis, and persistence. Here, we analyze the role of the PHA cycle in conferring robustness to the model bacterium P. putida KT2440. To assess the effect of this cycle in the cell, we began by constructing a PHA depolymerase (PhaZ) mutant strain that had its PHA cycle blocked. We then restored the flux through the cycle in the context of an engineered library of P. putida strains harboring differential levels of PhaZ. High-throughput phenotyping analyses of this collection of strains revealed significant changes in response to PHA cycle performance impacting cell number and size, PHA accumulation, and production of extracellular (R)-hydroxyalkanoic acids. To understand the metabolic changes at the system level due to PHA turnover, we contextualized these physiological data using the genome-scale metabolic model iJN1411. Model-based predictions suggest successive metabolic steady states during the growth curve and an important carbon flux rerouting driven by the activity of the PHA cycle. Overall, we demonstrate that modulating the activity of the PHA cycle gives us control over the carbon metabolism of P. putida, which in turn will give us the ability to tailor cellular mechanisms driving stress tolerance, e.g., defenses against oxidative stress, and any potential biotechnological applications. IMPORTANCE Despite large research efforts devoted to understanding the flexible metabolism of Pseudomonas beyond the role of key regulatory players, the metabolic basis powering the dynamic control of its biological fitness under disturbance conditions remains largely unknown. Among other metabolic hubs, the so-called PHA cycle, involving simultaneous synthesis and degradation of PHAs, is emerging as a pivotal metabolic trait powering metabolic robustness and resilience in this bacterial group. Here, we provide evidence suggesting that metabolic states in Pseudomonas can be anticipated, controlled, and engineered by tailoring the flux through the PHA cycle. Overall, our study suggests that the PHA cycle is a promising metabolic target toward achieving control over bacterial metabolic robustness. This is likely to open up a broad range of applications in areas as diverse as pathogenesis and biotechnology.

A review on enzymes and pathways for manufacturing polyhydroxybutyrate from lignocellulosic materials

Currently, major focus in the biopolymer field is being drawn on the exploitation of plant-based resources grounded on holistic sustainability trends to produce novel, affordable, biocompatible and environmentally safe polyhydroxyalkanoate biopolymers. The global PHA market, estimated at USD 62 Million in 2020, is predicted to grow by 11.2 and 14.2% between 2020-2024 and 2020-2025 correspondingly based on market research reports. The market is primarily driven by the growing demand for PHA products by the food packaging, biomedical, pharmaceutical, biofuel and agricultural sectors. One of the key limitations in the growth of the PHA market is the significantly higher production costs associated with pure carbon raw materials as compared to traditional polymers. Nonetheless, considerations such as consumer awareness on the toxicity of petroleum-based plastics and strict government regulations towards the prohibition of the use and trade of synthetic plastics are expected to boost the market growth rate. This study throws light on the production of polyhydroxybutyrate from lignocellulosic biomass using environmentally benign techniques via enzyme and microbial activities to assess its feasibility as a green substitute to conventional plastics. The novelty of the present study is to highlight the recent advances, pretreatment techniques to reduce the recalcitrance of lignocellulosic biomass such as dilute and concentrated acidic pretreatment, alkaline pretreatment, steam explosion, ammonia fibre explosion (AFEX), ball milling, biological pretreatment as well as novel emerging pretreatment techniques notably, high-pressure homogenizer, electron beam, high hydrostatic pressure, co-solvent enhanced lignocellulosic fractionation (CELF) pulsed-electric field, low temperature steep delignification (LTSD), microwave and ultrasound technologies. Additionally, inhibitory compounds and detoxification routes, fermentation downstream processes, life cycle and environmental impacts of recovered natural biopolymers, review green procurement policies in various countries, PHA strategies in line with the United Nations Sustainable Development Goals (SDGs) along with the fate of the spent polyhydroxybutyrate are outlined.

Process optimization, metabolic engineering interventions and commercialization of microbial polyhydroxyalkanoates production - A state-of-the art review

Microbial polyhydroxyalkanoates (PHAs) produced using renewable resources could be the best alternative for conventional plastics. Despite their incredible potential, commercial production of PHAs remains very low. Nevertheless, sincere attempts have been made by researchers to improve the yield and economic viability of PHA production by utilizing low-cost agricultural or industrial wastes. In this context, the use of efficient microbial culture or consortia, adoption of experimental design to trace ideal growth conditions, nutritional requirements, and intervention of metabolic engineering tools have gained significant attention. This review has been structured to highlight the important microbial sources for PHA production, use of conventional and non-conventional substrates, product optimization using experimental design, metabolic engineering strategies, and global players in the commercialization of PHA in the past two decades. The challenges about PHA recovery and analysis have also been discussed which possess indirect hurdle while expanding the horizon of PHA-based bioplastics. Selection of appropriate microorganism and substrate plays a vital role in improving the productivity and characteristics of PHAs. Experimental design-based bioprocess, use of metabolic engineering tools, and optimal product recovery techniques are invaluable in this dimension. Optimization strategies, which are being explored in isolation, need to be logically integrated for the successful commercialization of microbial PHAs.

Comparative analysis of various extraction processes based on economy, eco-friendly, purity and recovery of polyhydroxyalkanoate: A review

Bioplastics have been an interesting area of research and development in the last few decades. Normal plastics are made out of petroleum products, which is a non-renewable resource. Apart from that, its non-biodegradable nature makes it a serious threat to the environment, and hence a better alternative is needed. Bioplastics are synthesized by microorganisms and are biodegradable; this property makes them a promising alternative to normal plastic. However, the major drawback related to bioplastic is the high cost of its production. Polyhydroxyalkanoate (PHA) is a very popular biopolymer produced by different types of microbes. The review focuses on the different methods of extraction of PHA based on the percentage of purity, recovery, eco-friendly, and cost-effectiveness. There is a wide array of extraction methods reported to date, wherein there is the involvement of different types of solvents (like halogenated, non-halogenated, and green solvents) or mechanical or enzymatic methods. Each extraction process has its advantages and disadvantages. In this study, we have attempted to present a structured comparison of these different methods and highlight the factors that can be addressed for better extraction of PHA thereby making it a feasible alternative to commercial synthetic plastic.

Production of polyhydroxyalkanoates using dairy processing waste - A review

Bio-plastics are eco-friendly biopolymers finding tremendous application in the food and pharmaceutical industries. Bio-plastics have suitable physicochemical, mechanical properties, and do not cause any type of hazardous pollution upon disposal but have a high production cost. This can be minimized by screening potential bio-polymers producing strains, selecting inexpensive raw material, optimized cultivation conditions, and upstream processing. These bio-plastics specifically microbial-produced bio-polymers such as polyhydroxyalkanoates (PHAs) find application in food industries as packaging material owing to their desirable water barrier and gas permeability properties. The present review deals with the production, recovery, purification, characterization, and applications of PHAs. This is a comprehensive first review will also focus on different strategies adopted for efficient PHA production using dairy processing waste, its biosynthetic mechanism, metabolic engineering, kinetic aspects, and also biodegradability testing at the lab and pilot plant level. In addition to that, the authors will be emphasizing more on novel PHAs nanocomposites synthesis strategies and their commercial applicability.

Aquaculture Waste: Potential Synthesis of Polyhydroxyalkanoates

Petroleum-based plastics commonly and widely used on a daily basis are a threat to ecological health as they do not degrade in an ecologically feasible time frame. A class of natural polymers known as polyhydroxyalkanoates (PHAs) represents an up-and-coming alternative to petroleum-based materials, as they share properties similar to those of commodity plastics, such as polyethylene, polystyrene, among others, with the advantage of being biodegradable. PHAs are naturally produced by microorganisms under stress, and various farming practices have been proposed to be used for the synergistic and sustainable production of PHA for commercial purposes. Aquaculture has demonstrated particular potential for the production of PHA; however, a large struggle in commercializing these polymers is in procuring necessary feedstocks for manufacture outside of the laboratory environment. Through the coupling of PHA production and biofloc technology in aquaculture, the impediments to commercial exploitation can be potentially surmounted, while also providing for higher production efficiency in aquafarms. This mini-review covers the basic aspects of biofloc technology applied to aquaculture for the commercial production of PHA in large scale and offers a brief perspective on the next steps associated with the research and implementation of PHA production with biofloc technology.

Brewer's spent grain as a no-cost substrate for polyhydroxyalkanoates production: Assessment of pretreatment strategies and different bacterial strains

Polyhydroxyalkanoates (PHAs) are polyesters of significant interest due to their biodegradability and properties similar to petroleum-derived plastics, as well as the fact that they can be produced from renewable sources such as by-product streams. In this study, brewer's spent grain (BSG), the main by-product of the brewing industry, was subjected to a set of physicochemical pretreatments and their effect on the release of reducing sugars (RS) was evaluated. The RS obtained were used as a substrate for further PHA production in Burkholderia cepacia, Bacillus cereus, and Cupriavidus necator in liquid cultures. Although some pretreatments proved efficient in releasing RS (acid-thermal pretreatment up to 42.1 gRS L^-1 and 0.77 gRS g^-1 dried BSG), the generation of inhibitors in such scenarios likely affected PHA production compared with the process run without pretreatment (direct enzymatic hydrolysis of BSG). Thus, the maximum PHA accumulation from BSG hydrolysates was found in the reference case with 0.31 ± 0.02 g PHA per g cell dried weight, corresponding to 1.13 ± 0.06 g L^-1 and a PHA yield of 23 ± 1 mg g^-1 BSG. It was also found that C. necator presented the highest PHA accumulation of the tested strains followed closely by B. cepacia, reaching their maxima at 48 h. Although BSG has been used as a source for other bioproducts, these results show the potential of this by-product as a no-cost raw material for producing PHAs in a waste valorization and circular economy scheme.

Surface-Modified Highly Biocompatible Bacterial-poly(3-hydroxybutyrate-co-4-hydroxybutyrate): A Review on the Promising Next-Generation Biomaterial

Polyhydroxyalkanoates (PHAs) are bacteria derived bio-based polymers that are synthesised under limited conditions of nutritional elements with excess carbon sources. Among the members of PHAs, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [(P(3HB-co-4HB)] emerges as an attractive biomaterial to be applied in medical applications owing to its desirable mechanical and physical properties, non-genotoxicity and biocompatibility eliciting appropriate host tissue responses. The tailorable physical and chemical properties and easy surface functionalisation of P(3HB-co-4HB) increase its practicality to be developed as functional medical substitutes. However, its applicability is sometimes limited due to its hydrophobic nature due to fewer bio-recognition sites. In this review, we demonstrate how surface modifications of PHAs, mainly P(3HB-co-4HB), will overcome these limitations and facilitate their use in diverse medical applications. The integration of nanotechnology has drastically enhanced the functionality of P(3HB-co-4HB) biomaterials for application in complex biological environments of the human body. The design of versatile P(3HB-co-4HB) materials with surface modifications promise a non-cytotoxic and biocompatible material without inducing severe inflammatory responses for enhanced effective alternatives in healthcare biotechnology. The enticing work carried out with P(3HB-co-4HB) promises to be one of the next-generation materials in biomedicines which will facilitate translation into the clinic in the future.

Polyhydroxyalkanoate and its efficient production: an eco-friendly approach towards development

Polyhydroxyalkanoate (PHA) is the most promising solution to major ecological problem of plastic accumulation. The biodegradable and biocompatible properties of PHA make it highly demanding in the biomedical and agricultural field. The limited market share of PHA industries despite having tremendous demand as concerned with environment has led to knock the doors of scientific research for finding ways for the economic production of PHA. Therefore, new methods of its production have been applied such as using a wide variety of feedstock like organic wastes and modifying PHA synthesizing enzyme at molecular level. Modifying metabolic pathways for PHA production using new emerging techniques like CRISPR/Cas9 technology has simplified the process spending less amount of time. Using green solvents under pressurized conditions, ionic liquids, supercritical solvents, hypotonic cell disintegration for release of PHA granules, switchable anionic surfactants and even digestion of non-PHA biomass by animals are some novel strategies for PHA recovery which play an important role in sustainable production of PHA. Hence, this review provides a view of recent applications, significance of PHA and new methods used for its production which are missing in the available literature.

Upgrading end-of-line residues of the red seaweed Gelidium sesquipedale to polyhydroxyalkanoates using Halomonas boliviensis

Agar extraction from Gelidium and Gracilaria red seaweed species produces hundred thousand ton of carbohydrate-rich residues annually. Gelidium sesquipedale waste biomass obtained after agar extraction, still contained 44.2 % w/w total carbohydrates (dry-weight basis). These residues were biologically up-graded to poly-3-hydroxybutyrate (P3HB) after saccharification of their carbohydrate fraction to simple sugars. A combined hydrolysis treatment using sulfamic acid followed by enzymatic hydrolysis with cellulases produced a glucose-rich hydrolysate with a negligible content of inhibitors. With this treatment a sugar yield of circa 30 % (g glucose/g biomass) was attained. The algal hydrolysates were assessed as carbon source for the production of P3HB by the halotolerant bacteria Halomonas boliviensis. A cell concentration of 8.3 g L-1 containing 41 % (w/w) of polymer and a yield (YP/S ) of 0.16 gpolymer/gglucose were attained in shake flask assays. In this work, cellulose-rich seaweed waste was shown to be an upgradable, sustainable source of carbohydrates.

Cobetia sp. Bacteria, Which Are Capable of Utilizing Alginate or Waste Laminaria sp. for Poly(3-Hydroxybutyrate) Synthesis, Isolated From a Marine Environment

We isolated the Cobetia sp. strains IU 180733JP01 (5-11-6-3) and 190790JP01 (5-25-4-2) from seaweeds and showed that both strains accumulate poly(3-hydroxybutyrate) [P(3HB)] homopolymer in a nitrogen-limiting mineral salt medium containing alginate as a sole carbon source. Genome sequence analysis of the isolated strains showed that they have putative genes which encode enzymes relevant to alginate assimilation and P(3HB) synthesis, and the putative alginate-assimilating genes formed a cluster. Investigation of the optimum culture conditions for high accumulation of P(3HB) showed that when the 5-11-6-3 strain was cultured in a nitrogen-limiting mineral salt medium (pH 5.0) containing 6% NaCl and 3% (w/v) alginate as a sole carbon source for 2 days, the P(3HB) content and P(3HB) production reached 62.1 ± 3.4 wt% and 3.11 ± 0.16 g/L, respectively. When the 5-25-4-2 strain was cultured in a nitrogen-limiting mineral salt medium (pH 4.0) containing 5% NaCl and 3% (w/v) alginate for 2 days, the P(3HB) content and P(3HB) production reached 56.9 ± 2.1 wt% and 2.67 ± 0.11 g/L, respectively. Moreover, the 5-11-6-3 strain also produced P(3HB) in a nitrogen-limiting mineral salt medium (pH 5.0) containing 6% NaCl and freeze-dried and crushed waste Laminaria sp., which is classified into brown algae and contains alginate abundantly. The resulting P(3HB) content and P(3HB) productivity were 13.5 ± 0.13 wt% and 3.99 ± 0.15 mg/L/h, respectively. Thus, we demonstrated the potential application of the isolated strains to a simple P(3HB) production process from seaweeds without chemical hydrolysis and enzymatic saccharification.

Upgrading the organic fraction of municipal solid waste to poly(3-hydroxybutyrate)

The organic fraction of municipal solid waste was studied as feedstock for the production of poly(3-hydroxybutyrate) (P(3HB)). To release the monosaccharides, a diluted acid pre-treatment followed by an enzymatic hydrolysis was applied. A sugar yield of 49% was achieved using a pre-treated waste and an enzyme cocktail of Pentopan 500 BG and Celluclast BG. The addition of Glucoamylase NS 22035 helped to hydrolyze the starch fraction, improving the hydrolysis yield to 56%. The hydrolysate was used as culture medium to produce P(3HB) by Burkholderia sacchari DSM 17165. Assays at shaking flask scale showed that when the hydrolysate was used as substrate, the attained cell concentration was slightly higher than in the control medium. It was necessary to supplement the hydrolysate with extra glucose to increase the C/N ratio and with a mineral solution to overcome the nutritional deficiencies. The P(3HB) accumulation using the supplemented hydrolysate was 58% (g polymer/g biomass).

Scale Up Studies for Polyhydroxyalkanoate Production by a Bacillus flexus Strain with Industrial Potential

Polyhydroxyalkanoates (PHA) are synthesized by bacteria under unfavourable growth conditions like excess of carbon over nitrogen, coupled with oxygen limitation. The PHA polymers of microbial origin are diverse in chemical composition and material properties. A bioprocess for PHA production by indigenously isolated Bacillus flexus MTCC 12841 was devised and optimized at a laboratory fermentor scale. Fermentation strategies that involved modifications in some parameters like aeration, agitation, temperature, nutrient feeding or changes in C:N ratio led to substantial improvement of 59% in PHA production reaching highest concentration of 9.73 g/L. Biomass too was enhanced to 15.70 g/L equivalent to 126% increase over the optimized shake flask runs. PHA (Yp/s) and biomass (Yx/s) yields were found to be 0.32 and 0.51 g/g respectively, indicating good carbon utilization efficiency. The characterization of polymer by GC-MS revealed that the culture produced poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as a co-polymer. The novelty of the research findings lies in the demonstration of increased production of PHA at lab fermentor level coupled with the identification of the natural ability of the strain to also produce PHBV without any need for exogenous addition of precursors. The fermentation process as well as the strain may be subjected to further optimization to increase the PHA production as well as to increase the % of HV content in the co-polymer.

Nitrification and denitrification processes for mitigation of nitrous oxide from waste water treatment plants for biovalorization: Challenges and opportunities

Nitrous oxide (N₂O) is a potent greenhouse gas. Even though its emissions is much lesser than CO₂ but its global warming potential (GWP) is 298 times more than CO₂. N₂O emissions from wastewater treatment plants was caused due to incomplete nitrification or incomplete denitrification catalyzed by ammonia-oxidizing bacteria and heterotrophic denitrifiers. Low dissolved oxygen, high nitrite accumulation, change in optimal pH or temperature, fluctuation in C/N ratio, short solid retention time and non-availability of Cu ions were responsible for higher N₂O leakage. Regulation of enzyme metabolic pathways involved in N₂O production and reduction has also been reviewed. Sequential bioreactors, bioscrubbers, membrane biofilters usage have helped microbial nitrification-denitrification processes in succumbing N₂O production in wastewater treatment plants. Reduction of N₂O negativity has been studied through its valorization for the formation of value added products such as biopolymers has led to biorefinery approaches as an upcoming mitigation strategy.

Production and characterization of two medium-chain-length polydroxyalkanoates by engineered strains of Yarrowia lipolytica

Background

The oleaginous yeast Yarrowia lipolytica is an organism of choice for the tailored production of various compounds such as biofuels or biopolymers. When properly engineered, it is capable of producing medium-chain-length polyhydroxyalkanoate (mcl-PHA), a biobased and biodegradable polymer that can be used as bioplastics or biopolymers for environmental and biomedical applications.

Results

This study describes the bioproduction and the main properties of two different mcl-PHA polymers. We generated by metabolic engineering, strains of Y. lipolytica capable of accumulating more than 25% (g/g) of mcl-PHA polymers. Depending of the strain genetic background and the culture conditions, we produced (i) a mcl-PHA homopolymer of 3-hydroxydodecanoic acids, with a mass-average molar mass (M_w) of 316,000 g/mol, showing soft thermoplastic properties with potential applications in packaging and (ii) a mcl-PHA copolymer made of 3-hydroxyoctanoic (3HO), decanoic (3HD), dodecanoic (3HDD) and tetradecanoic (3TD) acids with a M_w of 128,000 g/mol, behaving like a thermoplastic elastomer with potential applications in biomedical material.

Conclusion

The ability to engineer Y. lipolytica to produce tailored PHAs together with the range of possible applications regarding their biophysical and mechanical properties opens new perspectives in the field of PHA bioproduction.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1140-y) contains supplementary material, which is available to authorized users.

Bio-Based Polymers for 3D Printing of Bioscaffolds

Three-dimensional (3D) printing technologies enable not only faster bioconstructs development but also on-demand and customized manufacturing, offering patients a personalized biomedical solution. This emerging technique has a great potential for fabricating bioscaffolds with complex architectures and geometries and specifically tailored for use in regenerative medicine. The next major innovation in this area will be the development of biocompatible and histiogenic 3D printing materials with bio-based printable polymers. This review will briefly discuss 3D printing techniques and their current limitations, with a focus on novel bio-based polymers as 3D printing feedstock for clinical medicine and tissue regeneration.

Wood-PHA Composites: Mapping Opportunities

Polyhydroxyalkanoate (PHA) biopolymers are emerging as attractive new sustainable polymers due to their true biodegradability and highly tuneable mechanical properties. However, despite significant investments, commercialisation barriers are hindering the capacity growth of PHA. In this work, we investigated the market potential for wood plastic composites (WPCs) based on PHAs. We considered the latest global production capacity of PHAs, estimated at 66,000 tonnes/year, and examined the implications of using PHAs for WPC production on the WPC market. Results indicate that a hypothetical usage of the current global PHA production for WPC manufacture would only represent the equivalent of 4.4% of the global WPC market, which is currently experiencing a 10.5% compounded annual growth rate. An economic assessment revealed that a wood-PHA composite as a drop-in alternative WPC product could cost as little as 37% of the cost of its neat PHA counterpart. Thus, WPCs with PHA offer a means to access benefits of PHA in engineering applications at reduced costs; however, further developments are required to improve strain at failure. The successful adoption of wood-PHA composites into the market is furthermore reliant on support from public sector to encourage biodegradable products where recycling is not a ready solution.

Draft Genome Sequence of the Endophyte Bacillus mycoides Strain GM5LP Isolated from Lolium perenne

Bacillus mycoides GM5LP is a Gram-positive endophytic bacterium isolated from aerial plant tissues of Lolium perenne L. The 6.0-Mb draft genome harbors 6,132 protein-coding sequences, some of which might be involved in the biosynthesis of antimicrobial substances.

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

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

Recent Advances and Challenges towards Sustainable Polyhydroxyalkanoate (PHA) Production

Sustainable biofuels, biomaterials, and fine chemicals production is a critical matter that research teams around the globe are focusing on nowadays. Polyhydroxyalkanoates represent one of the biomaterials of the future due to their physicochemical properties, biodegradability, and biocompatibility. Designing efficient and economic bioprocesses, combined with the respective social and environmental benefits, has brought together scientists from different backgrounds highlighting the multidisciplinary character of such a venture. In the current review, challenges and opportunities regarding polyhydroxyalkanoate production are presented and discussed, covering key steps of their overall production process by applying pure and mixed culture biotechnology, from raw bioprocess development to downstream processing.

Nitrous Oxide Abatement Coupled with Biopolymer Production As a Model GHG Biorefinery for Cost-Effective Climate Change Mitigation

N₂O represents ∼6% of the global greenhouse gas emission inventory and the most important O₃-depleting substance emitted in this 21st century. Despite its environmental relevance, little attention has been given to cost-effective and environmentally friendly N₂O abatement methods. Here we examined, the potential of a bubble column (BCR) and an internal loop airlift (ALR) bioreactors of 2.3 L for the abatement of N₂O from a nitric acid plant emission. The process was based on the biological reduction of N₂O by Paracoccus denitrificans using methanol as a carbon/electron source. Two nitrogen limiting strategies were also tested for the coproduction of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) coupled with N₂O reduction. High N₂O removal efficiencies (REs) (≈87%) together with a low PHBV cell accumulation were observed in both bioreactors in excess of nitrogen. However, PHBV contents of 38-64% were recorded under N limiting conditions along with N₂O-REs of ≈57% and ≈84% in the ALR and BCR, respectively. Fluorescence in situ hybridization analyses showed that P. denitrificans was dominant (>50%) after 6 months of experimentation. The successful abatement of N₂O concomitant with PHBV accumulation confirmed the potential of integrating biorefinery concepts into biological gas treatment for a cost-effective GHG mitigation.

Integrated systems for biopolymers and bioenergy production from organic waste and by-products: a review of microbial processes

Recently, issues concerning the sustainable and harmless disposal of organic solid waste have generated interest in microbial biotechnologies aimed at converting waste materials into bioenergy and biomaterials, thus contributing to a reduction in economic dependence on fossil fuels. To valorize biomass, waste materials derived from agriculture, food processing factories, and municipal organic waste can be used to produce biopolymers, such as biohydrogen and biogas, through different microbial processes. In fact, different bacterial strains can synthesize biopolymers to convert waste materials into valuable intracellular (e.g., polyhydroxyalkanoates) and extracellular (e.g., exopolysaccharides) bioproducts, which are useful for biochemical production. In particular, large numbers of bacteria, including Alcaligenes eutrophus, Alcaligenes latus, Azotobacter vinelandii, Azotobacter chroococcum, Azotobacter beijerincki, methylotrophs, Pseudomonas spp., Bacillus spp., Rhizobium spp., Nocardia spp., and recombinant Escherichia coli, have been successfully used to produce polyhydroxyalkanoates on an industrial scale from different types of organic by-products. Therefore, the development of high-performance microbial strains and the use of by-products and waste as substrates could reasonably make the production costs of biodegradable polymers comparable to those required by petrochemical-derived plastics and promote their use. Many studies have reported use of the same organic substrates as alternative energy sources to produce biogas and biohydrogen through anaerobic digestion as well as dark and photofermentation processes under anaerobic conditions. Therefore, concurrently obtaining bioenergy and biopolymers at a reasonable cost through an integrated system is becoming feasible using by-products and waste as organic carbon sources. An overview of the suitable substrates and microbial strains used in low-cost polyhydroxyalkanoates for biohydrogen and biogas production is given. The possibility of creating a unique integrated system is discussed because it represents a new approach for simultaneously producing energy and biopolymers for the plastic industry using by-products and waste as organic carbon sources.

Genome Structure ofBacillus cereustsu1 and Genes Involved in Cellulose Degradation and Poly-3-Hydroxybutyrate Synthesis

In previous work, we reported on the isolation and genome sequence analysis ofBacillus cereusstrain tsu1 NCBI accession number JPYN00000000. The 36 scaffolds in the assembled tsu1 genome were all aligned withB. cereusB4264 genome with variations. Genes encoding for xylanase and cellulase and the cluster of genes in the poly-3-hydroxybutyrate (PHB) biosynthesis pathway were identified in tsu1 genome. The PHB accumulation inB. cereustsu1 was initially identified using Sudan Black staining and then confirmed using high-performance liquid chromatography. Physical properties of these PHB extracts, when analyzed with Raman spectra and Fourier transform infrared spectroscopy, were found to be comparable to the standard compound. The five PHB genes in tsu1(phaA,phaB,phaR,phaC,andphaP)were cloned and expressed with TOPO cloning, and the recombinant proteins were validated using peptide mapping of in-gel trypsin digestion followed by mass spectrometry analysis. The recombinantE. coliBL21 (DE3) (over)expressingphaCwas found to accumulate PHB particles. The cellulolytic activity of tsu1 was detected using carboxymethylcellulose (CMC) plate Congo red assay and the shift towards low-molecular size forms of CMC revealed by gel permeation chromatography in CMC liquid culture and the identification of a cellulase in the secreted proteome.

Production kinetics of polyhydroxyalkanoates by using Pseudomonas aeruginosa gamma ray mutant strain EBN-8 cultured on soybean oil

The purpose of present study was to optimize polyhydroxyalkanotes (PHAs) production in a gamma ray mutant strain of Pseudomonas aeruginosa grown on soybean oil in minimal salts media under shake flask conditions. The production kinetics was studied by sampling on daily basis for 6 days to investigate the best conditions for PHAs production like biomass estimation, carbon source utilization and PHAs yield. The PHA accumulation was observed up to 50.27 % (w/w) of cell dry mass. The Pseudomonas species synthesized medium chain length PHA copolyester as per identified by LCMS and confirmed by FTIR spectroscopy. The ESI-MS analysis exhibited the major polyhydroxybutyrate with a molecular mass of m/z 448.5.