Whey valorization for sustainable polyhydroxyalkanoate production by Bacillus megaterium: Production, characterization and in vitro biocompatibility evaluation

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.

Production and characterization of polyhydroxybutyrate bioplastic precursor from Parageobacillus toebii using low-cost substrates and its potential antiviral activity

There is an increasing desire for bioplastics produced from renewable resources as an alternative to their petrochemical counterparts. These biopolymers have long-unnoticed antiviral properties. This study aimed to produce and characterize bioplastics by Parageobacillus toebii using low-cost substrates and determine their antiviral activity against coxsackievirus B4. Seven low-cost substrates (bagasse, water hyacinth, rice straw, rice water, sesame husks, molasses, and corn syrup) were compared with glucose for bioplastic precursor production. The highest bioplastic produced was from water hyacinth and glucose, followed by molasses, rice straw, rice water, sesame husks, and bagasse. Water hyacinth and glucose media were further optimized to increase the bioplastic precursor yield. The optimization of the media leads to increases in bioplastic precursor yields of 1.8-fold (3.456 g/L) and 1.496-fold (2.768 g/L), respectively. These bioplastics were further characterized by thermogravimetric analysis (TGA), Fourier-transformed infrared (FTIR) spectroscopy, proton nuclear magnetic resonance (1H NMR), and gas chromatography-mass spectrometry (GC-MS). They are thermostable, and their characterizations confirm the presence of polyhydroxybutyrate. The antiviral assay showed reasonable antiviral effects for bioplastics from water hyacinth (80.33 %) and glucose (55.47 %) media at 250 μg/mL maximum non-toxic concentrations (MNTC). The present investigation demonstrates a low-cost model for producing polyhydroxybutyrate bioplastic precursor for antiviral applications.

Production and characterization of polyhydroxyalkanoates by Halomonas alkaliantarctica utilizing dairy waste as feedstock

Currently, the global demand for polyhydroxyalkanoates (PHAs) is significantly increasing. PHAs are produced by several bacteria that are an alternative source of synthetic polymers derived from petrochemical refineries. This study established a simple and more feasible process of PHA production by Halomonas alkaliantarctica using dairy waste as the only carbon source. The data confirmed that the analyzed halophile could metabolize cheese whey (CW) and cheese whey mother liquor (CWML) into biopolyesters. The highest yield of PHAs was 0.42 g/L in the cultivation supplemented with CWML. Furthermore, it was proved that PHA structure depended on the type of by-product from cheese manufacturing, its concentration, and the culture time. The results revealed that H. alkaliantarctica could produce P(3HB-co-3HV) copolymer in the cultivations with CW at 48 h and 72 h without adding of any precursors. Based on the data obtained from physicochemical and thermal analyses, the extracted copolymer was reported to have properties suitable for various applications. Overall, this study described a promising approach for valorizing of dairy waste as a future strategy of industrial waste management to produce high value microbial biopolymers.

Poly(3-hydroxybutyrate) Production from Lignocellulosic Wastes Using Bacillus megaterium ATCC 14581

This study aimed to analyze the production of poly(3-hydroxybutyrate) (PHB) from lignocellulosic biomass through a series of steps, including microwave irradiation, ammonia delignification, enzymatic hydrolysis, and fermentation, using the Bacillus megaterium ATCC 14581 strain. The lignocellulosic biomass was first pretreated using microwave irradiation at different temperatures (180, 200, and 220 °C) for 10, 20, and 30 min. The optimal pretreatment conditions were determined using the central composite design (CCD) and the response surface methodology (RSM). In the second step, the pretreated biomass was subjected to ammonia delignification, followed by enzymatic hydrolysis. The yield obtained for the pretreated and enzymatically hydrolyzed biomass was lower (70.2%) compared to the pretreated, delignified, and enzymatically hydrolyzed biomass (91.4%). These hydrolysates were used as carbon substrates for the synthesis of PHB using Bacillus megaterium ATCC 14581 in batch cultures. Various analytical methods were employed, namely nuclear magnetic resonance (1H-NMR and13C-NMR), electrospray ionization mass spectrometry (EI-MS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), to identify and characterize the extracted PHB. The XRD analysis confirmed the partially crystalline nature of PHB.

Response surface optimization of poly-β-hydroxybutyrate synthesized by Bacillus cereus L17 using acetic acid as carbon source

A strain of Bacillus that can tolerate 10 g/L acetic acid and use the volatile fatty acids produced by the hydrolysis and acidification of activated sludge to produce polyhydroxyalkanoate was screened from the activated sludge of propylene oxide saponification wastewater. The strain was identified by 16S rRNA sequencing and phylogenetic tree analysis and was named Bacillus cereus L17. Various characterization methods showed that the polymer synthesized by strain L17 is poly-β-hydroxybutyrate, which has low crystallinity, good ductility and toughness, high thermal stability and a low polydispersity coefficient. It has wide thermoplastic material operating space as well as industrial and medicinal applications. The optimal fermentation conditions were determined by single factor optimization. Then, Plackett-Burman and Box-Behnken design experiments were carried out according to the single factor optimization results, and the response surface optimization was completed. The final results were: initial pH 6.7, temperature 25 °C, and loading volume 124 mL. The verification experiment showed that the yield of poly-β-hydroxybutyrate after optimization increased by 35.2 % compared to that before optimization.

The analysis of the function, diversity, and evolution of the Bacillus phage genome

BACKGROUND

Phages play a pivotal role in the evolution of microbial populations. The interactions between phages and their hosts are complex and may vary in response to host physiology and environmental conditions. Here, we have selected the genomes of some representative Bacillus prophages and lysosomes from the NCBI database for evolutionary analysis. We explored their evolutionary relationships and analyzed the protein information encoded by hundreds of Bacillus phages.

RESULTS

We obtained the following conclusions: First, Bacillus phages carried some known functional gene fragments and a large number of unknown functional gene fragments, which might have an important impact on Bacillus populations, such as the formation of spores and biofilms and the transmission of virulence factors. Secondly, the Bacillus phage genome showed diversity, with a clear genome boundary between Bacillus prophages and Bacillus lytic phages. Furthermore, genetic mutations, sequence losses, duplications, and host-switching have occurred during the evolution of the Bacillus phage, resulting in low genome similarity between the Bacillus phages. Finally, the lysis module played an important influence on the process of Bacillus phage cross-species infestation.

CONCLUSIONS

This study systematically described their protein function, diversity, and genome evolution, and the results of this study provide a basis for evolutionary diversity, horizontal gene transfer and co-evolution with the host in Bacillus phages.

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.

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.

Biotechnological interventions in food waste treatment for obtaining value-added compounds to combat pollution

Over the last few decades, the globe is facing tremendous effects due to the unnecessary piling of municipal solid waste among which food waste holds a greater portion. This practice not only affects the environment in terms of generating greenhouse gas emissions but when left dumped in landfills will also trigger poverty and malnutrition. This review focuses on the global trend in food waste management strategies involved in the effective utilization of food waste to produce various value-added products in a microbiology aspect, thereby diminishing the negative impacts caused by the unnecessary side effects of non-renewable energy sources. The review also detailed the efficiency of microorganisms in the production of various bio-energies as well. Further, recent attempts to the exploitation of genetically modified microorganisms in producing value-added products were enlisted. This also attempted to address food waste valorization techniques, the combined applications of various processes for an enhanced yield of different compounds, and addressed various challenges. Further, the current challenges involved in various processes and the effective measures to tackle them in the future have been addressed. Thus, the present review has successfully addressed the circular bio-economy in food waste valorization.

Biocatalytic conversion of a lactose-rich dairy waste into D-tagatose, D-arabitol and galactitol using sequential whole cell and fermentation technologies

Dairy industry waste has been explored as a cheap and attractive raw material to produce various commercially important rare sugars. In this study, a lactose-rich dairy byproduct, namely cheese whey powder (CWP), was microbially converted into three low caloric sweeteners using whole-cell and fermentation technologies. Firstly, the simultaneous lactose hydrolysis and isomerization of lactose-derived D-galactose into D-tagatose was performed by an engineered Escherichia coli strain co-expressing β-galactosidase and L-arabinose isomerase, which eventually produced 68.35 g/L D-tagatose during sequential feeding of CWP. Subsequently, the mixed syrup containing lactose-derived D-glucose and residual D-galactose was subjected to fermentation by Metschnikowia pulcherrima E1, which produced 60.12 g/L D-arabitol and 28.26 g/L galactitol. The net titer of the three rare sugars was 156.73 g/L from 300 g/L lactose (equivalent to 428.57 g/L CWP), which was equivalent to 1.12 mol product/mol lactose and 52.24% conversion efficiency in terms of lactose.

Turning mannitol-rich agricultural waste to poly(3-hydroxybutyrate) with Cobetia amphilecti fermentation and recovery with methyl levulinate as a green solvent

The present study explored the use of mannitol and mannitol-rich agro-industrial wastes as substrates for PHB production by Cobetia amphilecti isolated from the green Ulva sp. seaweed. Cultivation of C. amphilecti on mannitol, celery, and olive leaves (OLs) waste led to 4.20, 6.00, and 5.16 g L^-1 of cell dry mass (CDM), 76.3, 25.5, and 12.0% of PHB content in CDM and 3.2, 1.53, and 0.62 g L^-1 of PHB concentration, respectively; which suggested that they can be exploited as carbon substrates for the production of PHB. Extraction of PHB from C. amphilecti cultures by solubilization in the green solvent methyl levulinate (ML) (2% w/w, 140 °C, 1 h) indicated that the recovery yield and purity of PHB are above 97 and 90% w/w, respectively. The use of ML could be an attractive method for the recovery of PHB when safe and non-toxic solvents are required.

Pure cultures for synthetic culture development: Next level municipal waste treatment for polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs), as bio-based plastics, promise a transition from petroleum products to green and sustainable alternatives. However, their commercial production is yet impeded by high production costs. In this study, we assessed synthetic culture in mono and co-culture modes for bacterial PHA production. It was demonstrated that volatile fatty acids (VFAs) derived from food waste and primary sludge are cheap carbon sources for maintaining high production yields in the synthetic cultures. The maximum obtained PHA was 77.54 ± 5.67% of cell dried weight (CDW) (1.723 g/L) from Cupriavidus necator and 54.9 ± 3.66% of CDW (1.088 g/L) from Burkholderia cepacia. The acquired results are comparable to those in literature using sugar substrates. Comparatively, lower PHA productions were obtained from the co-cultivations ranging between 36-45 CDW% (0.39-0.48 g/L). Meanwhile, the 3-hydroxyvalerate content in the biopolymers were increased up to 21%.

Potential utilization of dairy industries by-products and wastes through microbial processes: A critical review

The dairy industry generates excessive amounts of waste and by-products while it gives a wide range of dairy products. Alternative biotechnological uses of these wastes need to be determined to aerobic and anaerobic treatment systems due to their high chemical oxygen demand (COD) levels and rich nutrient (lactose, protein and fat) contents. This work presents a critical review on the fermentation-engineering aspects based on defining the effective use of dairy effluents in the production of various microbial products such as biofuel, enzyme, organic acid, polymer, biomass production, etc. In addition to microbial processes, techno-economic analyses to the integration of some microbial products into the biorefinery and feasibility of the related processes have been presented. Overall, the inclusion of dairy wastes into the designed microbial processes seems also promising for commercial approaches. Especially the digestion of dairy wastes with cow manure and/or different substrates will provide a positive net present value (NPV) and a payback period (PBP) less than 10 years to the plant in terms of biogas production.

Valorization of dairy waste and by-products through microbial bioprocesses

Waste is an inherent and unavoidable part of any process which can be attributed to various factors such as process inefficiencies, usability of resources and discarding of not so useful parts of the feedstock. Dairy is a burgeoning industry following the global population growth, resulting in generation of waste such as wastewater (from cleaning, processing, and maintenance), whey and sludge. These components are rich in nutrients, organic and inorganic materials. Additionally, the presence of alkaline and acidic detergents along with sterilizing agents in dairy waste makes it an environmental hazard. Thus, sustainable valorization of dairy waste requires utilization of biological methods such as microbial treatment. This review brings forward the current developments in utilization and valorization of dairy waste through microbes. Aerobic and anaerobic treatment of dairy waste using microbes can be a sustainable and green method to generate biofertilizers, biofuels, power, and other biobased products.

Valorization of vinasse and whey to protein and biogas through an environmental fungi-based biorefinery

Vinasse and whey are wastewaters that are produced in large quantities in the sugar-to-ethanol and dairy industries, respectively. They pose a considerable threat to the environment due to the high concentration of nutrients and COD. In this study, the potential of producing protein-rich fungal biomass and biomethane from vinasse and whey through a two-stage biorefinery was examined. In the first stage, an edible and safe for human filamentous fungus, Neurospora intermedia, was cultivated on these wastewaters. To maximize the fungal biomass yield, the cultivation parameters, i.e., pH, vinasse to whey ratio, incubation time, and nutrients supplementation, were optimized. The highest yield of 12.0 g biomass per L of wastewaters was obtained by cultivation at pH 6.5 and vinasse to whey ratio of 25:75 (v/v) for 96 h with nitrogen source supplementation. The N. intermedia biomass contained about 45% protein and noticeable essential amino acid contents, comparable to commercial sources of protein for aquatic feed such as soybean meal and fishmeal. In the second stage, the effluent of fungal cultivation was anaerobically digested to produce 425 mL/g VS biomethane. Overall, 1 m³ of wastewater yielded 5.4 kg crude protein and 10.3 m³ methane, accompanied by 93.3% COD removal.

A Polyhydroxyalkanoates-Based Carrier Platform of Bioactive Substances for Therapeutic Applications

Bioactive substances (BAS), such as small molecule drugs, proteins, RNA, cells, etc., play a vital role in many therapeutic applications, especially in tissue repair and regeneration. However, the therapeutic effect is still a challenge due to the uncontrollable release and instable physico-chemical properties of bioactive components. To address this, many biodegradable carrier systems of micro-nano structures have been rapidly developed based on different biocompatible polymers including polyhydroxyalkanoates (PHA), the microbial synthesized polyesters, to provide load protection and controlled-release of BAS. We herein highlight the developments of PHA-based carrier systems in recent therapeutic studies, and give an overview of its prospective applications in various disease treatments. Specifically, the biosynthesis and material properties of diverse PHA polymers, designs and fabrication of micro- and nano-structure PHA particles, as well as therapeutic studies based on PHA particles, are summarized to give a comprehensive landscape of PHA-based BAS carriers and applications thereof. Moreover, recent efforts focusing on novel-type BAS nano-carriers, the functionalized self-assembled PHA granules in vivo, was discussed in this review, proposing the underlying innovations of designs and fabrications of PHA-based BAS carriers powered by synthetic biology. This review outlines a promising and applicable BAS carrier platform of novelty based on PHA particles for different medical uses.

Recent trends and developments on integrated biochemical conversion process for valorization of dairy waste to value added bioproducts: A review

In this review article, discuss the many ways utilized by the dairy sector to treat pollutants, emphasizing their influence on the quality and efficiency with which contamination is removed. It focuses on biotechnology possibilities for valorizing dairy waste in particular. The findings revealed that dairy waste may be treated using physicochemical, biological, and biotechnological techniques. Notably, this article highlighted the possibility of dairy waste being used as a feedstock not only for the generation of biogas, bioethanol, biohydrogen, microbial fuel cells, lactic acid, and fumaric acid via microbial technology but also for the production of biooil and biochar by pyrolysis. In addition, this article critically evaluates the many treatment techniques available for recovering energy and materials from dairy waste, their combinations, and implementation prospects. Valorization of dairy waste streams presents an opportunity to extend the dairy industry's presence in the fermented functional beverage sector.

A review on polyhydroxyalkanoate production from agricultural waste Biomass: Development, Advances, circular Approach, and challenges

Polyhydroxyalkanoates are biopolymers produced by microbial fermentation. They have excellent biodegradability and biocompatibility, which are regarded as promising substitutes for traditional plastics in various production and application fields. This review details the research progress in PHA production from lignocellulosic crop residues, lipid-type agricultural wastes, and other agro-industrial wastes such as molasses and whey. The effective use of agricultural waste can further reduce the cost of PHA production while avoiding competition between industrial production and food. The latest information on fermentation parameter optimization, fermentation strategies, kinetic studies, and circular approach has also been discussed. This review aims to analyze the crucial process of the PHA production from agricultural wastes to provide support and reference for further scale-up and industrial production.

Biopolymer poly-hydroxyalkanoates (PHA) production from apple industrial waste residues: A review

Apple pomace, the residue which is left out after processing of apple serves as a potential carbon source for the production of biopolymer, PHA (poly-hydroxyalkanoates). It is rich in carbohydrates, fibers and polyphenols. Utilization of these waste resources has dual societal benefit-waste management and conversion of waste to an eco-friendly biopolymer. This will lower the overall economics of the process. A major limitation for the commercialization of biopolymer in comparison with petroleum derived polymer is the high cost. This article gives an overview of valorization of apple pomace for the production of biopolymer, various strategies adopted, limitations as well as future perspectives.

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

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

Microbial valorization of underutilized and nonconventional waste streams

The growing burden of waste disposal coupled with natural resource scarcity has renewed interest in the remediation, valorization, and/or repurposing of waste. Traditional approaches such as composting, anaerobic digestion, use in fertilizers or animal feed, or incineration for energy production extract very little value out of these waste streams. In contrast, waste valorization into fuels and other biochemicals via microbial fermentation is an area of growing interest. In this review, we discuss microbial valorization of nonconventional, aqueous waste streams such as food processing effluents, wastewater streams, and other industrial wastes. We categorize these waste streams as carbohydrate-rich food wastes, lipid-rich wastes, and other industrial wastes. Recent advances in microbial valorization of these nonconventional waste streams are highlighted, along with a discussion of the specific challenges and opportunities associated with impurities, nitrogen content, toxicity, and low productivity.

Combinatorial approach for improved production of whole-cell 3-aminopropionic acid in recombinant Bacillus megaterium: codon optimization, gene duplication and process optimization

In this study, we aimed to develop a Bacillus megaterium based whole-cell biocatalyst for the bio-production of 3-aminopropionic acid (3-APA). l-aspartate-α-decarboxylases (ADC) (EC: 4.1.1.11) from Escherichia coli, B. megaterium, Corynebacterium glutamicum, and Bacillus subtilis were expressed in B. megaterium. B. subtilis derived ADC (panD _Bs ) exhibited the highest ADC activity of 0.9 ± 0.02 U/mL in recombinant B. megaterium. Combination of codon optimization and gene duplication strategies resulted in 415.56% enhancement of ADC activity compared to panD _Bs . The culture growth conditions of B. megaterium (BMD-7) for 3-APA production were optimized as follows: inducer concentration, 0.5% (w/v); time of induction, 3 h; induction temperature, 37 °C and post-induction incubation time, 8 h. Improvement of the whole-cell biocatalytic process efficiency, was dealt by optimization of reaction temperature, reaction pH, metal ion additives and l-aspartic acid concentration. Shake flask level experiments yielded an enhanced 3-APA titer (16.18 ± 0.26 g/L) and a yield of 0.89 g/g under optimized conditions viz., 45 °C, pH 6.0 and 20 g/L of l-aspartic acid. This study demonstrates the potential of B. megaterium for 3-APA production and paves the scope for the development of 3-APA producing strains in near future.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02885-7.

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.

Polyhydroxyalkanoates: Trends and advances toward biotechnological applications

Plastics are an integral part of most of the daily requirements. Indiscriminate usage and disposal have led to the accumulation of massive quantities of waste. Their non-biodegradable nature makes it increasingly difficult to manage and dispose them. To counter this impending disaster, biodegradable polymers, especially polyhydroxy-alkanoates (PHAs), have been envisaged as potential alternatives. Owing to their unique physicochemical characteristics, PHAs are gaining importance for versatile applications in the agricultural and medical sectors. Applications in the medical sector are more promising because of their commercial viability and sustainability. Despite such potential, their production and commercialization are significant challenges. The major limitations are their poor mechanical strength, production in small quantities, costly feed, and lack of facilities for industrial production. This article provides an overview of the contemporary progress in the field, to attract researchers and stakeholders to further exploit these renewable resources to produce biodegradable plastics on a commercial scale.

A comprehensive overview and recent advances on polyhydroxyalkanoates (PHA) production using various organic waste streams

Polyhydroxyalkanoates (PHA) are appealing as an important alternative to replace synthetic plastics owing to its comparable physicochemical properties to that of synthetic plastics, and biodegradable and biocompatible nature. This review gives an inclusive overview of the current research activities dealing with PHA production by utilizing different waste fluxes generated from food, milk and sugar processing industries. Valorization of these waste fluxes makes the process cost effective and practically applicable. Recent advances in the approaches adopted for waste treatment, fermentation strategies, and genetic engineering can give insights to the researchers for future direction of waste to bioplastics production. Lastly, synthesis and application of PHA-nanocomposites, research and development challenges, future perspectives for sustainable and cost-effective PHB production are also discussed. In addition, the review addresses the useful information about the opportunities and confines associated with the sustainable PHA production using different waste streams and their evaluation for commercial implementation within a biorefinery.

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.

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.

Waste to bioplastics: How close are we to sustainable polyhydroxyalkanoates production?

Increased awareness of environmental sustainability with associated strict environmental regulations has incentivized the pursuit of novel materials to replace conventional petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) are appealing intracellular biopolymers and have drawn significant attention as a viable alternative to petrochemical based plastics not only due to their comparable physiochemical properties but also, their outstanding characteristics such as biodegradability and biocompatibility. This review provides a comprehensive overview of the recent developments on the involved PHA producer microorganisms, production process from different waste streams by both pure and mixed microbial cultures (MMCs). Bio-based PHA production, particularly using cheap carbon sources with MMCs, is getting more attention. The main bottlenecks are the low production yield and the inconsistency of the biopolymers. Bioaugmentation and metabolic engineering together with cost effective downstream processing are promising approaches to overcome the hurdles of commercial PHA production from waste streams.

Critical overview of biomass feedstocks as sustainable substrates for the production of polyhydroxybutyrate (PHB)

Polyhydroxybutyrates (PHBs) are a class of biopolymers produced by different microbial species and are biodegradable and biocompatible in nature as opposed to petrochemically derived plastics. PHBs have advanced applications in medical sector, packaging industries, nanotechnology and agriculture, among others. PHB is produced using various feedstocks such as glycerol, dairy wastes, agro-industrial wastes, food industry waste and sugars. Current focus on PHB research has been primarily on reducing the cost of production and, on downstream processing to isolate PHB from cells. Recent advancements to improve the productivity and quality of PHB include genetic modification of producer strain and modification of PHB by blending to develop desirable properties suited to diversified applications. Selection of feedstock plays a critical role in determining the economic feasibility and sustainability of the process. This review provides a bird's eye view of the suitability of different waste resources for producing polyhydroxybutyrate; providing state-of the art information and analysis.