Optimization of critical factors to enhance polyhydroxyalkanoates (PHA) synthesis by mixed culture using Taguchi design of experimental methodology

Unlocking the potential of microbes: Concomitant production of polyhydroxyalkanoates and carotenoids

The escalating environmental concerns and depletion of crude oil resources have catalyzed interest in biologically derived polymers, particularly biodegradable ones such as polyhydroxyalkanoates. However, the high production costs associated with polyhydroxyalkanoates, driven by raw material expenses, stringent production conditions and low yields, hinder their widespread adoption. A potential strategy to mitigate these costs involves the production of PHAs and other high-value bioproducts, such as carotenoids simultaneously in microbial systems, utilizing shared metabolic pathways. Carotenoids, known for their antioxidant properties and applications in the food, cosmetics and pharmaceutical industries, offer substantial market potential. This review presents a comprehensive overview of the current progress in polyhydroxyalkanoate and carotenoid co-production, explores the co-synthesis pathways, addresses the challenges involved and explores the future prospects of this integrated bioprocess. By diversifying the product portfolio and optimizing microbial production systems, the co-production strategy could pave the way for more sustainable and economically viable bioplastics.

Controlled release of trifluralin herbicide using luminescent Vibrio-derived polyhydroxyalkanoate (PHA) microcapsules

The controlled release of herbicides using new and safe materials can mitigate environmental pollution. Polyhydroxyalkanoate (PHA) is a type of biopolymer that can be produced by various bacteria. It has properties that make it suitable for encapsulation and controlled release applications. A luminescent bacterium, Vibrio sp. VLC strain was used as the PHA producer in this study. Initially, the polymer was synthesized by the bacterium following optimization of the culture medium, resulting in an approximate yield of 25 %. Subsequently, the produced polymer was analyzed using TEM, FTIR, and H-NMR techniques. Microcapsules were produced using the emulsion method. FE-SEM imaging revealed spherical microcapsules with an average diameter of 0.5-2 μm. The herbicide loading content and encapsulation efficiency were determined to be 16.64 % and 66.56 %, respectively. The herbicidal effect of the microcapsules containing trifluralin was investigated using Amaranthus retroflexus and Setaria viridis plants, demonstrating a significant reduction in various parameters after application. Furthermore, the impact of encapsulated herbicide on soil microbial population was assessed, revealing a less negative effect compared to its free form. These findings suggest that the PHA from a luminescent vibrio holds promise as an eco-friendly, biodegradable, nontoxic material for the controlled release of herbicides.

Impact of Acetic Acid Supplementation in Polyhydroxyalkanoates Production by Cupriavidus necator Using Mixture-Process Design and Artificial Neural Network

The trend in bioplastic application has increased over the years where polyhydroxyalkanoates (PHAs) have emerged as a potential candidate with the advantage of being bio-origin, biodegradable, and biocompatible. The present study aims to understand the effect of acetic acid concentration (in combination with sucrose) as a mixture variable and its time of addition (process variable) on PHA production by Cupriavidus necator. The addition of acetic acid at a concentration of 1 g l-1 showed a positive influence on biomass and PHA yield; however, the further increase had a reversal effect. The addition of acetic acid at the time of incubation showed a higher PHA yield, whereas maximum biomass was achieved when acetic acid was added after 48 h. Genetic algorithm (GA) optimized artificial neural network (ANN) was used to model PHA concentration from mixture-process design data. Fitness of the GA-ANN model (R2: 0.935) was superior when compared to the polynomial model (R2: 0.301) from mixture design. Optimization of the ANN model projected 2.691 g l-1 PHA from 7.245 g l-1 acetic acid, 12.756 g l-1 sucrose, and the addition of acetic acid at the time of incubation. Sensitivity analysis indicates the inhibitory effect of all the predictors at higher levels. ANN model can be further used to optimize the variables while extending the bioprocess to fed-batch operation.

Perceiving biobased plastics as an alternative and innovative solution to combat plastic pollution for a circular economy

Plastic waste from fossil-based sources, including single-use packaging materials, is continuously accumulating in landfills, and leaching into the environment. A 2021 UN Environment Programme (UNEP) report suggests that the plastic pollution is likely to be doubled by 2030, posing a major challenge to the environment and the overall global plastic waste management efforts. The use of biobased plastics such as polyhydroxyalkanoates (PHAs) as a biodegradable substitute for petroleum-based plastics could be a feasible option to combat this issue which may further result in much lower carbon emissions and energy usage in comparison to conventional plastics as additional advantages. Though recent years have seen the use of microbes as biosynthetic machinery for biobased plastics, using various renewable feedstocks, the scaled-up production of such materials is still challenging. The current study outlays applications of biobased plastics, potential microorganisms producing biobased plastics such as Cupriavidus necator, Bacillus sp., Rhodopseudomonas palustris, microalgae, and mixed microbial cultures, and inexpensive and renewable resources as carbon substrates including industrial wastes. This review also provides deep insights into the operational parameters, challenges and mitigation, and future opportunities for maximizing the production of biobased plastic products. Finally, this review emphasizes the concept of biorefinery as a sustainable and innovative solution for biobased plastic production for achieving a circular bioeconomy.

Strategy for economical and enhanced polyhydroxyalkanoate production from synergistic utilization of palm oil and derived wastewater by activated sludge

The potential of palm oil and derived wastewater pretreated by enzyme as co-substrates to accumulate polyhydroxyalkanoate (PHA) rich in short and medium-chain-length monomers under two feeding strategies was evaluated batchwise through mixed microbial cultures (MMCs) in activated sludge. A terpolymer with the maximum PHA content of 30.5 wt%, volumetric yield of 0.372 g COD/g COD and composition of ca. 84.7 ∼ 97.4/0.5 ∼ 1.6/2.1 ∼ 13.7 (3-hydroxybutyrate/ 3-hydroxyvalerate/ 3-hydroxyoctanoate, %) was achieved as a result of co-substrate incorporation. From the perspective of economic benefits, PHA accumulated via adopting strategy of supplementing carbon source to the same initial concentration per cycle saved 42.7 % of carbon consumption, along with a reduction in culture time (72 h). The above discoveries signify that the combination of palm oil and derived wastewater plus MMCs provides an alternative to the plastics industries for a more sustainable and efficient utilization of biological resources and an economic PHA accumulation approach.

Construction of an artificial consortium of Escherichia coli and cyanobacteria for clean indirect production of volatile platform hydrocarbons from CO2

Ethylene and isoprene are essential platform chemicals necessary to produce polymers and materials. However, their current production methods based on fossil fuels are not very efficient and result in significant environmental pollution. For a successful transition more sustainable economic model, producing these key polymeric building blocks from renewable and sustainable resources such as biomass or CO2 is essential. Here, inspired by the symbiotic relationship of natural microbial communities, artificial consortia composed of E. coli strains producing volatile platform chemicals: ethylene and isoprene and two strains of cyanobacteria phototrophically synthesizing and exporting sucrose to feed these heterotrophs were developed. Disaccharide produced by transgenic cyanobacteria was used as a carbon and electron shuttle between the two community components. The E. coli cscB gene responsible for sucrose transport was inserted into two cyanobacterial strains, Thermosynechococcus elongatus PKUAC-SCTE542 and Synechococcus elongatus PCC7942, resulting in a maximal sucrose yield of 0.14 and 0.07       g/L, respectively. These organisms were co-cultured with E. coli BL21 expressing ethylene-forming enzyme or isoprene synthase and successfully synthesized volatile hydrocarbons. Productivity parameters of these co-cultures were higher than respective transgenic cultures of E. coli grown individually at similar sucrose concentrations, highlighting the positive impact of the artificial consortia on the production of these platform chemicals.

Optimization of Growth Conditions to Enhance PHA Production by Cupriavidus necator

The accumulation of polyhydroxyalkanoates (PHAs) by microorganisms usually occurs in response to environmental stress conditions. Therefore, it is advantageous to choose two-step cultivation. The first phase is aimed at maximizing biomass production, and only in the second phase, after setting the suitable conditions, PHA production starts. The aim of this work was to optimize the composition of the minimal propagation medium used for biomass production of Cupriavidus necator DSM 545 using the response surface methodology (RSM). Based on the results from the search for optimization limits, the glucose concentration, the ammonium sulfate concentration and the phosphate buffer molarity were chosen as independent variables. The optimal values were found as follows: the glucose concentration 10.8 g/L; the ammonium sulfate concentration 0.95 g/L; and the phosphate buffer molarity 60.2 mmol/L. The predicted biomass concentration was 4.54 g/L, and the verified value was at 4.84 g/L. Although this work was primarily focused on determining the optimal composition of the propagation medium, we also evaluated the optimal composition of the production medium and found that the optimal glucose concentration was 6.7 g/L; the ammonium sulfate concentration 0.60 g/L; and the phosphate buffer molarity 20 mmol/L. The predicted PHB yield was 54.7% (w/w) of dry biomass, and the verified value was 49.1%.

Kinetics and antimicrobial activity of gallic acid by novel bacterial co-culture system using Taguchi's method and submerged fermentation

A tannase-positive Bacillus gottheilii M2S2 and Bacillus cereus M1GT were co-cultivated for the production of gallic acid using tannic acid as the sole carbon source through submerged fermentation. Taguchi orthogonal array of design of experimental methodology was used to estimate the influence and significance of tannic acid concentration, glucose concentration, agitation speed, and inoculum size on the gallic acid production in a shake flask. Among all the factors, agitation speed contributed the highest for gallic acid production (28.28%), followed by glucose concentration (21.59%), inoculum size (19.6%), tannic acid concentration (19.54%), and pH (11.09%). Validation experiments were executed at the found optimized conditions which resulted in a 6.36-fold increase in gallic acid yield compared to unoptimized conditions. Further, the kinetics of growth, tannic acid degradation, and gallic acid yield were evaluated at the optimized conditions. The kinetic parameters Y x/s, Y p/s, and Y p/x were determined as 0.292 mg of cells/mg of tannic acid, 22.2 µg of gallic acid/mg of tannic acid, and 70.76 µg of gallic acid/mg of cells with a growth rate of 0.273 h -1 after 24 h of fermentation. Finally, the antimicrobial activity of the product gallic acid was investigated against food-borne pathogenic E. coli, S. aureus, and Serriatia marcescens and showed a zone of inhibition of 2 cm, 1.6 cm, and 1.3 cm, respectively, using the agar disc diffusion technique. Thus, the cost-effective bioproduct gallic acid proved to be potentially effective to control food poisoning diseases and preserve foodstuff.

Efficient and economical production of polyhydroxyalkanoate from sustainable rubber wood hydrolysate and xylose as co-substrate by mixed microbial cultures

Using co-substrate to accumulate polyhydroxyalkanoate (PHA) is an efficient approach to reduce production cost and improve yield of PHA. In the study, PHA was biosynthesized under full aerobic mode by using rubber wood hydrolysate and xylose co-substrate as the carbon source. The effects of co-substrate on PHA production, microbial community and carbon conversion were explored. The results showed that proper addition of xylose was beneficial for the synthesis of PHA and monomer 3-hydroxyvalerate (3HV). Higher conversion yield of substrate-to-PHA (Y_PHA/S) of 0.933 g COD PHA/g COD S and PHA content of 43.6 g PHA/100 g VSS were gained at co-substrate ratio of 1:1. Likewise, under this condition, PHA production also reached the highest value of 1849 mg COD/L (1088 mg/L). Moreover, the addition of xylose created a favorable screening of PHA dominant strains, improved the conversion of carbon source, and saved 72.3% of feedstock consumption.

Review of the Developments of Bacterial Medium-Chain-Length Polyhydroxyalkanoates (mcl-PHAs)

Synthetic plastics derived from fossil fuels—such as polyethylene, polypropylene, polyvinyl chloride, and polystyrene—are non-degradable. A large amount of plastic waste enters landfills and pollutes the environment. Hence, there is an urgent need to produce biodegradable plastics such as polyhydroxyalkanoates (PHAs). PHAs have garnered increasing interest as replaceable materials to conventional plastics due to their broad applicability in various purposes such as food packaging, agriculture, tissue-engineering scaffolds, and drug delivery. Based on the chain length of 3-hydroxyalkanoate repeat units, there are three types PHAs, i.e., short-chain-length (scl-PHAs, 4 to 5 carbon atoms), medium-chain-length (mcl-PHAs, 6 to 14 carbon atoms), and long-chain-length (lcl-PHAs, more than 14 carbon atoms). Previous reviews discussed the recent developments in scl-PHAs, but there are limited reviews specifically focused on the developments of mcl-PHAs. Hence, this review focused on the mcl-PHA production, using various carbon (organic/inorganic) sources and at different operation modes (continuous, batch, fed-batch, and high-cell density). This review also focused on recent developments on extraction methods of mcl-PHAs (solvent, non-solvent, enzymatic, ultrasound); physical/thermal properties (Mw, Mn, PDI, Tm, Tg, and crystallinity); applications in various fields; and their production at pilot and industrial scales in Asia, Europe, North America, and South America.

Scale-Up Studies for Polyhydroxyalkanoate and Halocin Production by <i>Halomonas</i> Sp. as Potential Biomedical Materials

Polyhydroxyalkanoates (PHA) are the biomaterials isolated naturally from bacterial strains. These are present in granules and accumulated intracellularly for storage and energy uptake in stressed conditions. This work was based on the extraction of polyhydroxyalkanoates from haloarchaeal strains isolated from samples of a salt mine and Halocin activity screening of these isolates. For the screening of polyhydroxyalkanoates, Nile Blue and Sudan Black Staining were performed. After confirmation and theoretical determination, polyhydroxyalkanoates extraction was done by sodium hypochlorite digestion and solvent extraction by chloroform method in combination. Polyhydroxyalkanoates production was calculated along with the determination of biomass. Halocin activity of these strains was also screened at different intervals. Isolated strains were identified by 16S RNA gene sequencing. Polyhydroxyalkanoates polymer was produced in form of biofilms and brittle crystals. Halocin activity was exhibited by four strains, among which confirmed halocin activity was shown by strain K7. The remarkable results showed that polyhydroxyalkanoates can replace synthetic plastics which are not environment friendly as they cause environmental pollution – a major threat to Earth rising gradually. Therefore, by switching to the use of biodegradable bioplastics from the use of synthetic plastics, it would be beneficial to the ecosphere.

Plastic waste management practices pertaining to India with particular focus on emerging technologies

Under the parent petrochemical industries, plastic industry is proliferating enormously over the past several years globally due to its advantages in terms of weight, robustness, expense, versatility, and durability. Due to the diversified consumer base representing varied climate zones, food habits, and standards of living, the generation and growth opportunities for the plastic industry in India are particularly distinct and humongous. The present work extensively reviews the Indian plastic industry with primary focus on the evolving technologies for plastic waste valorization encompassing their level of utilization, technology readiness, and progress achieved at R&D level. The study attempts to recognize different issues related to technology, recycling, policy, research, regulation that should be given attention to formulate an improved plastic waste management strategy in the region. Though significant shares of waste plastics in the country are processed by traditional practices, state-of-the-art technologies primarily plastic to oil conversion, in road making and in cement manufacturing, are being deployed at increasing rate. Action to tackle the problem of plastic contamination in India will need to adopt a pan India strategic consensus/concurrent approach for effective waste collection and segregation with active participation of urban local bodies, fixing the role of the informal sectors, investment for reliable technology adoption with skilled manpower for operation, adoption of circular economy schemes involving plastic waste co-processing, and providing support to work on R&D for better penetration of the proven plastic valorization options along with their environmental and social implications.

A Glimpse of the World of Volatile Fatty Acids Production and Application: A review

Sustainable provision of chemicals and materials is undoubtedly a defining factor in guaranteeing economic, environmental, and social stability of future societies. Among the most sought-after chemical building blocks are volatile fatty acids (VFAs). VFAs such as acetic, propionic, and butyric acids have numerous industrial applications supporting from food and pharmaceuticals industries to wastewater treatment. The fact that VFAs can be produced synthetically from petrochemical derivatives and also through biological routes, for example, anaerobic digestion of organic mixed waste highlights their provision flexibility and sustainability. In this regard, this review presents a detailed overview of the applications associated with petrochemically and biologically generated VFAs, individually or in mixture, in industrial and laboratory scale, conventional and novel applications.

Optimization of Propagation Medium for Enhanced Polyhydroxyalkanoate Production by Pseudomonas oleovorans

Polyhydroxyalkanoates (PHAs) represent a promising alternative to commercially used petroleum-based plastics. Pseudomonas oleovorans is a natural producer of medium-chain-length PHA (mcl-PHA) under cultivation conditions with nitrogen limitation and carbon excess. Two-step cultivation appears to be an efficient but more expensive method of PHA production. Therefore, the aim of this work was to prepare a minimal synthetic medium for maximum biomass yield and to optimize selected independent variables by response surface methodology (RSM). The highest biomass yield (1.71 ± 0.04 g/L) was achieved in the optimized medium containing 8.4 g/L glucose, 5.7 g/L sodium ammonium phosphate and 35.4 mM phosphate buffer. Under these conditions, both carbon and nitrogen sources were completely consumed after 48 h of the cultivation and the biomass yield was 1.7-fold higher than in the conventional medium recommended by the literature. This approach demonstrates the possibility of using two-stage PHA cultivation to obtain the maximum amount of biomass and PHA.

Simultaneous biosynthesis of bacterial polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS): Process optimization and Scale-up

Owing to their biodegradability and renewability, biopolymers are being employed in industrial and bio-medical sectors as sustainable alternatives to chemical based polymers. In the present study, isolated Providencia sp. depicted dual production of intra and extracellular biopolymers, polyhydroxybutyrate (PHB) and extracellular polymeric substances (EPS), respectively. The polymer production process was optimised by varying process parameters such as carbon load (20, 30 and 40 g L^-1) and pH (6, 7 and 8) for enhancing PHB and EPS productivity. Maximum yield of both PHB (2.62 g L^-1) and EPS (3.92 g L^-1) was observed with carbon load of 30 g L^-1 at pH 7. Scale-up studies were performed with optimized conditions and PHB and EPS production of 2.62 g L^-1 and 3.91 g L^-1, respectively was observed. The extracted EPS and PHB were characterized using FT-IR, FE-SEM-EDX, H¹ and C¹³ NMR and fluorescence microscopy.

Beyond PHA: Stimulating intracellular accumulation of added-value compounds in mixed microbial cultures

This review compiled and analyzed the operational conditions (dissolved oxygen, feast and famine ratio, sequential batch reactor cycle length, organic loading rate (OLR), pH, C/N, and temperature) established during the feast and famine culture strategy for the mixed microbial cultures (MMC) selection to understand how these variables could affect the synthesis of polyhydroxyalkanoates, polyglucose, triacylglycerides, levulinic acid and adipic acid from non-fermented substrates. According to the reported information, the dissolved oxygen has a greater impact on the type and amount of produced compound. In a lesser extent, the OLR and the cycle length were identified to have an impact on the accumulation of polyhydroxyalkanoates, whose accumulation was favored at lower OLR and longer cycle lengths. Thereby, the information of this work will allow the design of future strategies for the simultaneous accumulation of compounds of interest other than the polyhydroxyalkanoates or understand the operational conditions that would optimize the polyhydroxyalkanoates production.

The Synthesis, Characterization and Applications of Polyhydroxyalkanoates (PHAs) and PHA-Based Nanoparticles

Polyhydroxyalkanoates (PHAs) are storage granules found in bacteria that are essentially hydroxy fatty acid polyesters. PHA molecules appear in variety of structures, and amongst all types of PHAs, polyhydroxybutyrate (PHB) is used in versatile fields as it is a biodegradable, biocompatible, and ecologically safe thermoplastic. The unique physicochemical characteristics of these PHAs have made them applicable in nanotechnology, tissue engineering, and other biomedical applications. In this review, the optimization, extraction, and characterization of PHAs are described. Their production and application in nanotechnology are also portrayed in this review, and the precise and various production methods of PHA-based nanoparticles, such as emulsion solvent diffusion, nanoprecipitation, and dialysis are discussed. The characterization techniques such as UV-Vis, FTIR, SEM, Zeta Potential, and XRD are also elaborated.

Polyhydroxybutyrate production from dark-fermentative effluent and composite grafting with bagasse derived α-cellulose in a biorefinery approach

The study evaluated the preparation of a biocomposite using waste-derived polyhydroxybutyrate (PHB) and bagasse cellulose (α-cellulose) in a biorefinery approach. PHB was produced using dark fermentation effluent rich in volatile fatty acids (VFA) derived from vegetable waste and α-cellulose was extracted from sugarcane bagasse (SCB). Nutrient limitation induced microbial PHB accumulation, wherein maximum production of 0.28 ± 0.06 g PHB/g DCW (28%) was observed. Confocal examination showed the deposition of PHB granules in the cell cytoplasm and NMR spectrum exhibited a structural correlation. α-Cellulose (0.22 ± 0.02 g α-cellulose/g SCB) was extracted through SCB pretreatment. Thereafter, grafting α-cellulose with PHB offered intermolecular bonding, which resulted in enhanced thermal stability of the biocomposite than corresponding pristine PHB. FE-SEM morphological examination of biocomposite depicted that α-cellulose functioned as a filler to PHB. XRD profiles showed significant decrement in PHB crystallinity, signifying the functional role of α-cellulose as an effective reinforcing agent. Additionally, ether functional group of α-cellulose and ester group of PHB also appeared in XPS analysis of the composite, thus authorizing the effective blending of α-cellulose and PHB. Utilization of bagasse-derived cellulose for strengthening biologically produced PHB expands its applications, while simultaneously addressing the plastic pollution issues. Additional value from this process was further achieved by incorporating the concept of biorefinery, wherein acidogenic fermentation effluents were used for the production of PHA, which enabled the re-entry of products (VFA) to the production cycle, thus achieving circularity.

Recent developments in short- and medium-chain- length Polyhydroxyalkanoates: Production, properties, and applications

Developing renewable resource-based plastics with complete biodegradability and a minimal carbon footprint can open new opportunities to effectively manage the end-of-life plastics waste and achieve a low carbon society. Polyhydroxyalkanoates (PHAs) are biobased and biodegradable thermoplastic polyesters that accumulate in microorganisms (e.g., bacterial, microalgal, and fungal species) as insoluble and inert intracellular inclusion. The PHAs recovery from microorganisms, which typically involves cell lysis, extraction, and purification, provides high molecular weight and purified polyesters that can be compounded and processed using conventional plastics converting equipment. The physio-chemical, thermal, and mechanical properties of the PHAs are comparable to traditional synthetic polymers such as polypropylene and polyethylene. As a result, it has attracted substantial applications interest in packaging, personal care, coatings, agricultural and biomedical uses. However, PHAs have certain performance limitations (e.g. slow crystallization), and substantially more expensive than many other polymers. As such, more research and development is required to enable them for extensive use. This review provides a critical review of the recent progress achieved in PHAs production using different microorganisms, downstream processing, material properties, processing avenues, recycling, aerobic and anaerobic biodegradation, and applications.

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 and biochar from green macroalgal Ulva sp. biomass subcritical hydrolysates: Process optimization and a priori economic and greenhouse emissions break-even analysis

Although macroalgae biomass is an emerging sustainable feedstock for biorefineries, the optimum process parameters for their hydrolysis and fermentation are still not known. In the present study, the simultaneous production of polyhydroxyalkanoates (PHA) and biochar from green macroalgae Ulva sp. is examined, applying subcritical water hydrolysis and Haloferax mediterranei fermentation. First, the effects of temperature, treatment time, salinity, and solid load on the biomass and PHA productivity were optimized following the Taguchi method. Hydrolysis at 170 °C, 20 min residence time, 38 g L^-1 salinity with a seaweed solid load of 5% led to the maximum PHA yield of 0.104 g g^-1Ulva and a biochar yield of 0.194 ± 1.23 g g^-1Ulva. Second, the effect of different initial culture densities on the biomass and PHA productivity was studied. An initial culture density of 50 g L^-1 led to the maximum volumetric PHA productivity of 0.024 ± 0.002 g L^-1 h^-1 with a maximum PHA content of 49.38 ± 0.3% w/w Sensitivity analysis shows that within 90% confidence, the annual PHA production from Ulva sp. is 148.14 g PHA m^-2 year^-1 with an annual biochar production of 42.6 g m^-2 year^-1. Priori economic and greenhouse gas break-even analyses of the process were done to estimate annual revenues and allowable greenhouse gas emissions. The study illustrates that PHA production from seaweed hydrolysate using extreme halophiles coupled to biochar production could become a benign and promising step in a marine biorefinery.

Developing Lactic Acid Bacteria as an Oral Healthy Food

Lactic acid bacteria have functions in immunoregulation, antagonism, and pathogen inhibition. The purpose of this study was to evaluate the effectiveness of lactic acid bacteria (LAB) in countering oral pathogens and develop related products. After a series of assays to 450 LAB strains, 8 heat-inactivated strains showed a strong inhibitory effect on a caries pathogen, Streptococcus mutans, and 308 heat-inactivated LAB strains showed a strong inhibitory effect on a periodontal pathogen, Porphyromonas gingivalis. The key reasons for inhibiting oral pathogens were bacteriocins produced by LAB and the coaggregation effect of the inactivated cells. We selected Lacticaseibacillus (Lb) paracasei 111 and Lb.paracasei 141, which had the strongest inhibitory effects on the above pathogens, was the main oral health food source. The optimal cultural conditions of Lb. paracasei 111 and Lb. paracasei 141 were studied. An oral tablet with a shelf life of 446 days made of the above strains was developed. A 40 volunteers' clinical study (CSMUH IRB number: CS05065) was conducted with this tablet in the Periodontological Department of the Stomatology Research Center, Affiliated Hospital of Chung Shan Medical University (Taiwan). After 8 weeks of testing, 95% and 78.9% of patients showed an effect on reducing periodontal pathogens and improving probing pocket depth, respectively, in the oral tablet group.

Key role of different levels of dissolved oxygen in hydrolyzed polyacrylamide bioconversion: Focusing on metabolic products, key enzymes and functional microorganisms

Dissolved oxygen (DO) played a short board effect on nitrogen biotransformation and pollutant metabolism. This study for the first time explored the key role of different levels of DO (covering anaerobic, anoxic and aerobic) on hydrolyzed polyacrylamide (HPAM) bioconversion. HPAM was metabolized to intermediates with different chain length. Volatile fatty acid (VFA) production rose first and then descended with DO concentration (0-2 mg·L-1), and the maximum reached 92.5 mg·L-1 when DO was 0.5 mg·L-1. Total nitrogen (TN) removal increased first and then dropped with DO concentration, and the maximum (61.4%) occurred at 0.5 mg·L-1 DO. NH4+-N dipped from 42.8 to 0 mg·L-1 and NO3--N rose from 0 to 32.8 mg·L-1 with DO concentration. The changes of enzyme activities were consistent with those of VFA production and TN removal, which were related to HPAM metabolism and N bioconversion. Microbial function was correlated to HPAM metabolism, N bioconversion and key enzyme.

Recovery of polyhydroxyalkanoates (PHAs) from wastewater: A review

Polyhydroxyalkanoates (PHAs) are biopolyesters accumulated as carbon and energy storage materials under unbalanced growth conditions by various microorganisms. They are one of the most promising potential substitutes for conventional non-biodegradable plastics due to their similar physicochemical properties, but most important, its biodegradability. Production cost of PHAs is still a great barrier to extend its application at industrial scale. In order to reduce that cost, research is focusing on the use of several wastes as feedstock (such as agro-industrial and municipal organic waste and wastewater) in a platform based on mixed microbial cultures. This review provides a critical illustration of the state of the art of the most likely-to-be-scale-up PHA production processes using mixed microbial cultures platform and waste streams as feedstock, with a particular focus on both, upstream and downstream processes. Current pilot scale studies, future prospects, challenges and developments in the field are also highlighted.

Polyhydroxyalkanoates (PHA) production from fermented thermal-hydrolyzed sludge by PHA-storing denitrifiers integrating PHA accumulation with nitrate removal

Polyhydroxyalkanoates (PHA) production from fermented thermal-hydrolyzed sludge was conducted by mixed microbial cultures (MMCs) in the study. An MMC enriched in the species Brachymonas_denitrificans (60.18%) was selected under an aerobic feast/famine regime, which is capable of denitrification and accumulating PHA. To take advantage of the PHA-storing denitrifiers, an aerobic-feast/anoxic-famine regime was applied to integrate culture selection with denitrification. The results showed that cultures enriched under the regime exhibited a PHA storage capacity with PHA yield on VFA of 0.47 gCOD/gCOD and well denitrification performance achieving nitrate removal of 98%. Moreover, the aerobic-feast/anoxic-famine regime could originate a comparable maximum PHA content to the complete aerobic feast/famine regime (49.7 wt% versus. 47.1 wt%, respectively), yet reduce aeration energy input by 79% in the culture selection process. Finally, this study investigated the accumulation of nitrite and nitrous oxide during PHA based denitrification and the feasibility of integrating the process with wastewater treatment.

Optimal iron concentrations for growth-associated polyhydroxyalkanoate biosynthesis in the marine photosynthetic purple bacterium Rhodovulum sulfidophilum under photoheterotrophic condition

Polyhydroxyalkanoates (PHAs) are a group of natural biopolyesters that resemble petroleum-derived plastics in terms of physical properties but are less harmful biologically to the environment and humans. Most of the current PHA producers are heterotrophs, which require expensive feeding materials and thus contribute to the high price of PHAs. Marine photosynthetic bacteria are promising alternative microbial cell factories for cost-effective, carbon neutral and sustainable production of PHAs. In this study, Rhodovulum sulfidophilum, a marine photosynthetic purple nonsulfur bacterium with a high metabolic versatility, was evaluated for cell growth and PHA production under the influence of various media components found in previous studies. We evaluated iron, using ferric citrate, as another essential factor for cell growth and efficient PHA production and confirmed that PHA production in R. sulfidophilum was growth-associated under microaerobic and photoheterotrophic conditions. In fact, a subtle amount of iron (1 to 2 μM) was sufficient to promote rapid cell growth and biomass accumulation, as well as a high PHA volumetric productivity during the logarithmic phase. However, an excess amount of iron did not enhance the growth rate or PHA productivity. Thus, we successfully confirmed that an optimum concentration of iron, an essential nutrient, promotes cell growth in R. sulfidophilum and also enhances PHA utilization.

Mixed culture polyhydroxyalkanoate (PHA) synthesis from nutrient rich wet oxidation liquors

Organic waste residues can be hydrothermally treated to produce organic acid rich liquors. These hydrothermal liquors are a potential feedstock for polyhydroxyalkanoate (PHA) production. We investigated the effect of dissolved oxygen concentration and substrate feeding regimes on PHA accumulation and yield using two hydrothermal liquors derived from a mixture of primary and secondary municipal wastewater treatment sludge and food waste. The enriched culture accumulated a maximum of 41% PHA of cell dry weight within 7 h; which is among the highest reported for N and P rich hydrothermal liquors. Recovered PHA was 77% polyhydroxybutyrate and 23% polyhydroxyvalerate by mass. The families Rhodocyclaceae (84%) and Saprospiraceae (20.5%) were the dominant Proteobacteria (73%) in the enriched culture. The third most abundant bacterial genus, Bdellovibrio, includes species of known predators of PHA producers which may lead to suboptimal PHA accumulation. The PHA yield was directly proportional to DO concentration for ammonia stripped liquor (ASL) and inversely proportional to DO concentration for low strength liquor (LSL). The highest yield of 0.50 Cmol PHA/Cmol substrate was obtained for ASL at 25% DO saturation. A progressively increasing substrate feeding regime resulted in increased PHA yields. These findings demonstrate that substrate feeding regime and oxygen concentration can be used to control the PHA yield and accumulation rate thereby enhancing PHA production viability from nutrient rich biomass streams.

Bioprocess optimization of PHB homopolymer and copolymer P3 (HB-co-HV) by Acinetobacter junii BP25 utilizing rice mill effluent as sustainable substrate

The potential use of parboiled rice mill effluent as a cheap substrate for the production of homopolymer and copolymer of Polyhydroxyalkanoates (PHAs) by Acinetobacter junii BP 25 was investigated for the first time. Process optimization by one factor at a time led to homopolymer polyhydroxybutyrate (PHB) production of 2.64 ± 0.18 g/l with 94.28% PHB content using a two-stage batch cultivation mode. BP 25 furthermore produced polyhydroxybutyrate-co-hydroxyvalerate (P3 (HB-co-HV)), with the addition of valeric acid as an additive to the substrate, yielding (2.56 ± 0.12 g/l dry biomass, 2.20 ± 0.15 g/l PHA) a copolymer content of 85.93%. Thus, rice mill effluent can be an effective and relatively low-cost alternative for the production of PHA, replacing the pure substrates.

Isolation and Characterization of PHA-Producing Bacteria from Propylene Oxide Saponification Wastewater Residual Sludge

A polyhydroxyalkanoate (PHA)-producing strain was isolated from propylene oxide (PO) saponification wastewater activated sludge and was identified as Brevundimonas vesicularis UJN1 through 16S rDNA sequencing and Biolog microbiological identification. Single-factor and response surface methodology experiments were used to optimize the culture medium and conditions. The optimal C/N ratio was 100/1.04, and the optimal carbon and nitrogen sources were sucrose (10 g/L) and NH₄Cl (0.104 g/L) respectively. The optimal culture conditions consisted of initial pH of 6.7 and an incubation temperature of 33.4 °C for 48 h, with 15% inoculum and 100 mL medium at an agitation rate of 180 rpm. The PHA concentration reached 34.1% of the cell dry weight and increased three times compared with that before optimization. The only report of PHA-producing bacteria by Brevundimonas vesicularis showed that the conversion rate of PHAs using glucose as the optimal carbon source was 1.67%. In our research, the conversion rate of PHAs with sucrose as the optimal carbon source was 3.05%, and PHA production using sucrose as the carbon source was much cheaper than that using glucose as the carbon source.

Polyhydroxyalkanoates (PHA) production from synthetic waste using Pseudomonas pseudoflava: PHA synthase enzyme activity analysis from P. pseudoflava and P. palleronii

Synthetic wastewater (SW) at various carbon concentrations (5-60g/l) were evaluated for polyhydroxyalkanoates (PHA) production using the bacteria Pseudomonas pseudoflava. Bacteria showed highest PHA production with 20g/l (57±5%), and highest carbon removal at 5g/l (74±6%) concentrations respectively. Structure, molecular weight, and thermal properties of the produced PHA were evaluated using various analytical techniques. Bacteria produced homo-polymer [poly-3-hydroxybutyrate (P3HB)] when only acetate was used as carbon source; and it produced co-polymer [poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV)] by addition of co-substrate propionate. PHA synthase, the enzyme which produce PHA was extracted from two bacterial strains i.e., P. pseudoflava and P. palleronii and its molecular weight was analysed using SDS-PAGE. Protein concentration, and PHA synthase enzyme activity of P. pseudoflava and P. palleronii was carried out using spectrophotometer. Results denoted that P. pseudoflava can be used for degradation of organic carbon persistent in wastewaters and their subsequent conversion into PHA.

Enrichment of a mixed microbial culture for polyhydroxyalkanoates production: Effect of pH and N and P concentrations

Polyhydroxyalkanoates (PHA) are biopolymers that can be an alternative against conventional plastics. The study reported herein evaluated the enrichment of a mixed microbial culture (MMC) operated under feast/famine regime and different pHs in a sequencing batch reactor (SBR) using acetate as sole carbon source to produce polyhydroxyalkanoates (PHAs). The enrichment step was evaluated at controlled pH of 7.5 and also without pH control (averaged value of 9.0). The acetate uptake rate (-q_S) of both enrichments at the end of the experimental period exhibited similar behaviour being about 0.18CmolAcCmolX^-1h^-1 and 0.19CmolAcCmolX^-1h^-1 for SBR-A and SBR-B, respectively. However, the PHA-storing capacity of the biomass enriched without pH control was better, exhibiting a maximum PHA content of 36% (gPHAg^-1 VSS) with a PHA production rate (q_PHA) of 0.16CmolPHACmolX^-1h^-1. Batch experiments were performed to evaluate PHA-storing capacity of the enriched culture at different pHs and nutrients concentrations. In the pH experiments (without nutrient limitation), it was found that in the absence of controlled pH, the enriched biomass exhibited a PHA content of 44% gPHAg^-1 VSS with -q_S and PHA to substrate yield (Y_PHA/Ac) of 0.57CmolAcCmolX^-1h^-1 and 0.33CmolPHACmolAc^-1, respectively. Regarding the experiments at variable nutrients concentration (pH ranging 8.8 to 9.2), the results indicate that the PHA content in the enriched biomass is significantly higher being around 51% gPHAg^-1 VSS under nitrogen limitation. This work demonstrated the feasibility of the enrichment of a MMC with PHA storage ability without pH control. Results also suggest that better PHAs contents and substrate uptake rates are obtained without controlling the pH in the accumulation step. Finally, this work also highlights the importance of understanding the role of nutrients concentration during the accumulation step.

Production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) from synthetic wastewater using Hydrogenophaga palleronii

In the present study, synthetic wastewater (SW) was used for production of poly-3-hydroxybutyrate (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) using the bacteria Hydrogenophaga palleronii. SW at various volatile fatty acids concentrations (5-60g/l) was evaluated for the growth and biopolymer production using H. palleronii. Substrate degradation was analyzed using total organic carbon (TOC) analyzer and high pressure liquid chromatography (HPLC). H. palleronii showed highest and lowest removal of TOC at 5g/l (88±4%) and 60g/l (15±6%) respectively. Among all the concentrations evaluated, bacteria showed highest biopolymer production with 20g/l (63±5%), followed by 30g/l (58±3%) and 40g/l (56±2%). Lowest biopolymer production was observed at 5g/l concentration (21±3%). Structure, molecular weight, and thermal properties of the produced biopolymer were analyzed. These results denoted that the strain H. palleronii can be used for degradation of high concentration of volatile fatty acids persistent in wastewaters and their subsequent conversion into useable biopolymers.

Exploitation of Food Industry Waste for High-Value Products

A growing global population leads to an increasing demand for food production and the processing industry associated with it and consequently the generation of large amounts of food waste. This problem is intensified due to slow progress in the development of effective waste management strategies and measures for the proper treatment and disposal of waste. Food waste is a reservoir of complex carbohydrates, proteins, lipids, and nutraceuticals and can form the raw materials for commercially important metabolites. The current legislation on food waste treatment prioritises the prevention of waste generation and least emphasises disposal. Recent valorisation studies for food supply chain waste opens avenues to the production of biofuels, enzymes, bioactive compounds, biodegradable plastics, and nanoparticles among many other molecules.

Poly-3-hydroxybutyrate (PHB) production from alkylphenols, mono and poly-aromatic hydrocarbons using Bacillus sp. CYR1: A new strategy for wealth from waste

In the present study five different types of alkylphenols, each of the two different types of mono and poly-aromatic hydrocarbons were selected for degradation, and conversion into poly-3-hydroxybutyrate (PHB) using the Bacillus sp. CYR1. Strain CYR1 showed growth with various toxic organic compounds. Degradation pattern of all the organic compounds at 100 mg/l concentration with or without addition of tween-80 were analyzed using high pressure liquid chromatography (HPLC). Strain CYR1 showed good removal of compounds in the presence of tween-80 within 3 days, but it took 6 days without addition of tween-80. Strain CYR1 showed highest PHB production with phenol (51 ± 5%), naphthalene (42 ± 4%), 4-chlorophenol (32 ± 3%) and 4-nonylphenol (29 ± 3%). The functional groups, structure, and thermal properties of the produced PHB were analyzed. These results denoted that the strain Bacillus sp. CYR1 can be used for conversion of different toxic compounds persistent in wastewaters into useable biological polyesters.

Pseudomonas pseudoalcaligenes CECT5344, a cyanide-degrading bacterium with by-product (polyhydroxyalkanoates) formation capacity

BACKGROUND

Cyanide is one of the most toxic chemicals produced by anthropogenic activities like mining and jewelry industries, which generate wastewater residues with high concentrations of this compound. Pseudomonas pseudoalcaligenes CECT5344 is a model microorganism to be used in detoxification of industrial wastewaters containing not only free cyanide (CN(-)) but also cyano-derivatives, such as cyanate, nitriles and metal-cyanide complexes. Previous in silico analyses suggested the existence of genes putatively involved in metabolism of short chain length (scl-) and medium chain length (mcl-) polyhydroxyalkanoates (PHAs) located in three different clusters in the genome of this bacterium. PHAs are polyesters considered as an alternative of petroleum-based plastics. Strategies to optimize the bioremediation process in terms of reducing the cost of the production medium are required.

RESULTS

In this work, a biological treatment of the jewelry industry cyanide-rich wastewater coupled to PHAs production as by-product has been considered. The functionality of the pha genes from P. pseudoalcaligenes CECT5344 has been demonstrated. Mutant strains defective in each proposed PHA synthases coding genes (Mpha(-), deleted in putative mcl-PHA synthases; Spha(-), deleted in the putative scl-PHA synthase) were generated. The accumulation and monomer composition of scl- or mcl-PHAs in wild type and mutant strains were confirmed by gas chromatography-mass spectrometry (GC-MS). The production of PHAs as by-product while degrading cyanide from the jewelry industry wastewater was analyzed in batch reactor in each strain. The wild type and the mutant strains grew at similar rates when using octanoate as the carbon source and cyanide as the sole nitrogen source. When cyanide was depleted from the medium, both scl-PHAs and mcl-PHAs were detected in the wild-type strain, whereas scl-PHAs or mcl-PHAs were accumulated in Mpha(-) and Spha(-), respectively. The scl-PHAs were identified as homopolymers of 3-hydroxybutyrate and the mcl-PHAs were composed of 3-hydroxyoctanoate and 3-hydroxyhexanoate monomers.

CONCLUSIONS

These results demonstrated, as proof of concept, that talented strains such as P. pseudoalcaligenes might be applied in bioremediation of industrial residues containing cyanide, while concomitantly generate by-products like polyhydroxyalkanoates. A customized optimization of the target bioremediation process is required to gain benefits of this type of approaches.

Anaerobic digestion of bio-waste: A mini-review focusing on territorial and environmental aspects

Scientific and industrial experiences, together with economical and policies changes of last 30 years, bring anaerobic digestion among the most environmental friendly and economically advantageous technologies for organic waste treatment and management in Europe. In this short review, the role of anaerobic digestion of organic wastes is discussed, considering the opportunity of a territorial friendly approach, without barriers, where different organic wastes are co-treated. This objective can be achieved through two proposed strategies: one is the anaerobic digestion applied as a service for the agricultural and farming sector; the other as a service for citizen (biowaste, diapers and wastewater treatment integration). The union of these two strategies is an environmental- and territorial-friendly process that aims to produce renewable energy and fertiliser material, with a low greenhouse gas emission and nutrients recovery. The advantage of forthcoming application of anaerobic digestion of organic wastes, even for added value bioproducts production and new energy carriers, are finally discussed. Among several advantages of anaerobic digestion, the role of the environmental controller was evaluated, considering the ability of minimising the impacts exploiting the biochemical equilibrium and sensitivity as a quality assurance for digestate.

Enhanced polyhydroxyalkanoate production from organic wastes via process control

This work explores the use of a model-based control scheme to enhance the productivity of polyhroxyalkanoate (PHA) production in a mixed culture two-stage system fed with synthetic wastewater. The controller supplies pulses of substrate while regulating the dissolved oxygen (DO) concentration and uses the data to fit a dynamic mathematical model, which in turn is used to predict the time until the next pulse addition. Experiments in a bench scale system first determined the optimal DO set-point and initial substrate concentration. Then the proposed feedback control strategy was compared with a simpler empiric algorithm. The results show that a substrate conversion rate of 1.370±0.598mgPHA/mgCOD/d was achieved. The proposed strategy can also indicate when to stop the accumulation of PHA upon saturation, which occurred with a PHA content of 71.0±7.2wt.%.

Biotechnological Production of Polyhydroxyalkanoates: A Review on Trends and Latest Developments

Polyhydroxyalkanoates (PHA) producers have been reported to reside at various ecological niches which are naturally or accidently exposed to high organic matter or growth limited conditions such as dairy wastes, hydrocarbon contaminated sites, pulp and paper mill wastes, agricultural wastes, activated sludges of treatment plants, rhizosphere, and industrial effluents. Few among them also produce extracellular by-products like rhamnolipids, extracellular polymeric substances, and biohydrogen gas. These sorts of microbes are industrially important candidates for the reason that they can use waste materials of different origin as substrate with simultaneous production of valuable bioproducts including PHA. Implementation of integrated system to separate their by-products (intracellular and extracellular) can be economical in regard to production. In this review, we have discussed various microorganisms dwelling at different environmental conditions which stimulate them to accumulate carbon as polyhydroxyalkanoates granules and factors influencing its production and composition. A brief aspect on metabolites which are produced concomitantly with PHA has also been discussed. In conclusion, exploring of capabilities like of dual production by microbes and use of wastes as renewable substrate under optimized cultural conditions either in batch or continuous process can cause deduction in present cost of bioplastic production from stored PHA granules.