Biorefining of protein waste for production of sustainable fuels and chemicals

Whole genome sequencing and characterization of Pantoea agglomerans DBM 3797, endophyte, isolated from fresh hop (Humulus lupulus L.)

Background

This paper brings new information about the genome and phenotypic characteristics of Pantoea agglomerans strain DBM 3797, isolated from fresh Czech hop (Humulus lupulus) in the Saaz hop-growing region. Although P. agglomerans strains are frequently isolated from different materials, there are not usually thoroughly characterized even if they have versatile metabolism and those isolated from plants may have a considerable potential for application in agriculture as a support culture for plant growth.

Methods

P. agglomerans DBM 3797 was cultured under aerobic and anaerobic conditions, its metabolites were analyzed by HPLC and it was tested for plant growth promotion abilities, such as phosphate solubilization, siderophore and indol-3-acetic acid productions. In addition, genomic DNA was extracted, sequenced and de novo assembly was performed. Further, genome annotation, pan-genome analysis and selected genome analyses, such as CRISPR arrays detection, antibiotic resistance and secondary metabolite genes identification were carried out.

Results and discussion

The typical appearance characteristics of the strain include the formation of symplasmata in submerged liquid culture and the formation of pale yellow colonies on agar. The genetic information of the strain (in total 4.8 Mb) is divided between a chromosome and two plasmids. The strain lacks any CRISPR-Cas system but is equipped with four restriction-modification systems. The phenotypic analysis focused on growth under both aerobic and anaerobic conditions, as well as traits associated with plant growth promotion. At both levels (genomic and phenotypic), the production of siderophores, indoleacetic acid-derived growth promoters, gluconic acid, and enzyme activities related to the degradation of complex organic compounds were found. Extracellular gluconic acid production under aerobic conditions (up to 8 g/l) is probably the result of glucose oxidation by the membrane-bound pyrroloquinoline quinone-dependent enzyme glucose dehydrogenase. The strain has a number of properties potentially beneficial to the hop plant and its closest relatives include the strains also isolated from the aerial parts of plants, yet its safety profile needs to be addressed in follow-up research.

Biological importance of arginine: A comprehensive review of the roles in structure, disorder, and functionality of peptides and proteins

Arginine shows Jekyll and Hyde behavior in several respects. It participates in protein folding via ionic and H-bonds and cation-pi interactions; the charge and hydrophobicity of its side chain make it a disorder-promoting amino acid. Its methylation in histones; RNA binding proteins; chaperones regulates several cellular processes. The arginine-centric modifications are important in oncogenesis and as biomarkers in several cardiovascular diseases. The cross-links involving arginine in collagen and cornea are involved in pathogenesis of tissues but have also been useful in tissue engineering and wound-dressing materials. Arginine is a part of active site of several enzymes such as GTPases, peroxidases, and sulfotransferases. Its metabolic importance is obvious as it is involved in production of urea, NO, ornithine and citrulline. It can form unusual functional structures such as molecular tweezers in vitro and sprockets which engage DNA chains as part of histones in vivo. It has been used in design of cell-penetrating peptides as drugs. Arginine has been used as an excipient in both solid and injectable drug formulations; its role in suppressing opalescence due to liquid-liquid phase separation is particularly very promising. It has been known as a suppressor of protein aggregation during protein refolding. It has proved its usefulness in protein bioseparation processes like ion-exchange, hydrophobic and affinity chromatographies. Arginine is an amino acid, whose importance in biological sciences and biotechnology continues to grow in diverse ways.

Black soldier fly (Hermetia illucens) larvae as potential feedstock for the biodiesel production: Recent advances and challenges

Black soldier fly larvae (BSFL) Hermetia illucens is fastest growing and most promising insect species especially recommended to bring high-fat content as 5th generation bioenergy. The fat content can be fully optimized during the life-cycle of the BSFL through various organic dietary supplements and environmental conditions. Enriched fat can be obtained during the larval stages of the BSF. The presence of high saturated and unsaturated fatty acids in their body helps to produce 70 % of extractable oil which can be converted into biodiesel through transesterification. The first-generation biodiesel process mainly depends on catalytic transesterification, however, BSFL had 94 % of biodiesel production through non-catalytic transesterification. This increases the sustainability of producing biodiesel with less energy input in the process line. Other carbon emitting factors involved in the rearing of BSFL are less than the other biodiesel feedstocks including microalgae, cooking oil, and non-edible oil. Therefore, this review is focused on evaluating the optimum dietary source to produce fatty acid rich larvae and larval growth to accumulate C16-18 fatty acids in larger amounts from agro food waste. The process of optimization and biorefining of lipids using novel techniques have been discussed herein. The sustainability impact was evaluated from the cultivation to biodiesel conversion with greenhouse gas emissions scores in the entire life-cycle of process flow. The state-of-the-art in connecting circular bioeconomy loop in the search for bioenergy was meticulously covered.

Green Biomass-Based Protein for Sustainable Feed and Food Supply: An Overview of Current and Future Prospective

It is necessary to develop and deploy novel protein production to allow the establishment of a sustainable supply for both humans and animals, given the ongoing expansion of protein demand to meet the future needs of the increased world population and high living standards. In addition to plant seeds, green biomass from dedicated crops or green agricultural waste is also available as an alternative source to fulfill the protein and nutrient needs of humans and animals. The development of extraction and precipitation methods (such as microwave coagulation) for chloroplast and cytoplasmic proteins, which constitute the bulk of leaf protein, will allow the production of leaf protein concentrates (LPC) and protein isolates (LPI). Obtained LPC serves as a sustainable alternative source of animal-based protein besides being an important source of many vital phytochemicals, including vitamins and substances with nutritional and pharmacological effects. Along with it, the production of LPC, directly or indirectly, supports sustainability and circular economy concepts. However, the quantity and quality of LPC largely depend on several factors, including plant species, extraction and precipitation techniques, harvest time, and growing season. This paper provides an overview of the history of green biomass-derived protein from the early green fodder mill concept by Károly Ereky to the state-of-art of green-based protein utilization. It highlights potential approaches for enhancing LPC production, including dedicated plant species, associated extraction methods, selection of optimal technologies, and best combination approaches for improving leaf protein isolation.

Glutamate as a non-conventional substrate for high production of the recombinant protein in Escherichia coli

The economic viability of the biomass-based biorefinery is readily acknowledged by implementation of a cascade process that produces value-added products such as enzymes prior to biofuels. Proteins from the waste stream of biorefinery processes generally contain glutamate (Glu) in abundance. Accordingly, this study was initiated to explore the potential of Glu for production of recombinant proteins in Escherichia coli. The approach was first adopted by expression of D-hydantoinase (HDT) in commercially-available BL21(DE3) strain. Equipped with the mutant gltS (gltS*), the strain grown on Glu produced the maximum HDT as compared to the counterpart on glucose, glycerol, or acetate. The Glu-based production scheme was subsequently reprogrammed based on the L-arabinose-regulated T7 expression system. The strain with gltS* was further engineered by rewiring metabolic pathways. With low ammonium, the resulting strain produced 1.63-fold more HDT. The result indicates that Glu can serve as a carbon and nitrogen source. Overall, our proposed approach may open up a new avenue for the enzyme biorefinery platform based on Glu.

Recovery of sugars and amino acids from brewers' spent grains using subcritical water hydrolysis in a single and two sequential semi-continuous flow-through reactors

This study evaluated the subcritical water hydrolysis (SWH) of brewer's spent grains (BSG) to obtain sugars and amino acids. The experimental conditions investigated the hydrolysis of BSG in a single flow-through reactor and in two sequential reactors operated in semi-continuous mode. The hydrolysis experiments were carried out for 120 min at 15 MPa, 5 mL water min^-1, at different temperatures (80 - 180 °C) and using an S/F of 20 and 10 g solvent g^-1 BSG, for the single and two sequential reactors, respectively. The highest monosaccharide yields were obtained at 180 °C in a single reactor (47.76 mg g^-1 carbohydrates). With these operational conditions, the hydrolysate presented xylose (0.477 mg mL^-1) and arabinose (1.039 mg mL^-1) as main sugars, while low contents of furfural (310.7 µg mL^-1), 5-hydroxymethylfurfural (<1 mg L^-1), and organic acids (0.343 mg mL^-1) were obtained. The yield of proteins at 180 °C in a process with a single reactor was 43.62 mg amino acids g^-1 proteins, where tryptophan (215.55 µg mL^-1), aspartic acid (123.35 µg mL^-1), valine (64.35 µg mL^-1), lysine (16.55 µg mL^-1), and glycine (16.1 µg mL^-1) were the main amino acids recovered in the hydrolysate. In conclusion, SWH pretreatment is a promising technology to recover bio-based compounds from BSG; however, further studies are still needed to increase the yield of bioproducts from lignocellulosic biomass to explore two sequential reactors.

R, Maitra S, Tarafdar A, Alphy MP, Kumar AN, Madhavan A, Sirohi R, Awasthi MK, Sindhu R, Varjani S, Binod P. Waste-Derived Fuels and Renewable Chemicals for Bioeconomy Promotion: A Sustainable Approach

Bio-based fuels and chemicals through the biorefinery approach has gained significant interest as an alternative platform for the petroleum-derived processes as these biobased processes are noticed to have positive environmental and societal impacts. Decades of research was involved in understanding the diversity of microorganisms in different habitats that could synthesize various secondary metabolites that have functional potential as fuels, chemicals, nutraceuticals, food ingredients, and many more. Later, due to the substrate-related process economics, the diverse low-value, high-carbon feedstocks like lignocellulosic biomass, industrial byproducts, and waste streams were investigated to have greater potential. Among them, municipal solid wastes can be used as the source of substrates for the production of commercially viable gaseous and liquid fuels, as well as short-chain fattyacids and carboxylic acids. In this work, technologies and processes demanding the production of value-added products were explained in detail to understand and inculcate the value of municipal solid wastes and the economy, and it can provide to the biorefinery aspect.

Production of Lignocellulolytic Enzymes and Phenolic Compounds by Lentinus strigosus from the Amazon Using Solid-State Fermentation (SSF) of Guarana (Paullinia cupana) Residue

The Amazon rainforest has a rich biodiversity, and studies of Basidiomycete fungi that have biomolecules of biotechnological interest are relevant. The use of lignocellulosic biomass in biotechnological processes proposes an alternative use, and also adds value to the material when employed in the bioconversion of agro-industrial waste. In this context, this study evaluate the production of lignocellulolytic enzymes (carboxymethylcellulases (CMCase), xylanase, pectinase, laccase) as well as phenolic compounds and proteases by solid-state fermentation (SSF) using the fungus Lentinus strigosus isolated from Amazon. The guarana (Paullinia cupana) residue was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). SSF was carried out with 60% humidification of the residue, at 30 °C, for 10 days. The lignocellulosic biomass presented fragmented structures with irregular shapes and porosities, and was mainly constituted by cellulose (19.16%), hemicellulose (32.83%), and lignin (6.06%). During the SSF, significant values of CMCase (0.84 U/g) on the 8th day, xylanase (1.00 U/g) on the 7th day, pectinase (2.19 U/g) on the 6th day, laccase (176.23 U/mL) on the 5th day, phenolic compounds (10.27 μg/mL) on the 1st day, soluble proteins (0.08 mg/mL) on the 5th day, and protease (8.30 U/mL) on the 6th day were observed. In general, the agro-industrial residue used provided promising results as a viable alternative for use as a substrate in biotechnological processes.

Chemoselective Transfer Hydrogenation of Enamides Using Ru Pincer Complexes for the Synthesis of α-Amino Acids

The chemoselective reduction of enamides to α-amino acids with iPrOH and EtOH as H-donors and solvents catalyzed by Ru pincer complexes is demonstrated. A range of α-amino acids is synthesized in good to excellent yields. Applications, large scale, and a one-pot experiment are also reported. Finally, deuterium-labeling experiments show high regioselectivity between the α- and β-positions of the alkene unit.

Algae biorefinery: a promising approach to promote microalgae industry and waste utilization

Microalgae have a number of intriguing characteristics that make them a viable raw material aimed at usage in a variety of applications when refined using a bio-refining process. They offer unique capabilities that allow them to be used in biotechnology-related applications. As a result, this review explores how to increase the extent to which microalgae may be integrated with various additional biorefinery uses in order to improve their maintainability. In this study, the use of microalgae as potential animal feed, manure, medicinal, cosmeceutical, ecological, and other biotechnological uses is examined in its entirety. It also includes information on the boundaries, openings, and improvements of microalgae and the possibilities of increasing the range of microalgae through techno-economic analysis. According to the findings of this review, financing supported research and shifting the focus of microalgal investigations from biofuels production to biorefinery co-products can help guarantee that they remain a viable resource. Furthermore, innovation collaboration is unavoidable if one wishes to avoid the high cost of microalgae biomass handling. This review is expected to be useful in identifying the possible role of microalgae in biorefinery applications in the future.

Bioprocesses for the recovery of bioenergy and value-added products from wastewater: A review

Wastewater and activated sludge present a major challenge worldwide. Wastewater generated from large and small-scale industries, laundries, human residential areas and other sources is emerging as a main problem in sanitation and maintenance of smart/green cities. During the last decade, different technologies and processes have been developed to recycle and purify the wastewater. Currently, identification and fundamental consideration of development of more advanced microbial-based technologies that enable wastewater treatment and simultaneous resource recovery to produce bioenergy, biofuels and other value-added compounds (organic acids, fatty acids, bioplastics, bio-pesticides, bio-surfactants and bio-flocculants etc.) became an emerging topic. In the last several decades, significant development of bioprocesses and techniques for the extraction and recovery of mentioned valuable molecules and compounds from wastewater, waste biomass or sludge has been made. This review presents different microbial-based process routes related to resource recovery and wastewater application for the production of value-added products and bioenergy. Current process limitations and insights for future research to promote more efficient and sustainable routes for this under-utilized and continually growing waste stream are also discussed.

High-throughput integrated pretreatment strategies to convert high-solid loading microalgae into high-concentration biofuels

The commercial feasibility of energy-efficient conversion of highly concentrated microalgal suspensions to produce high-titer biofuels is a major bottleneck due to high energy consumption. Herein, high-titer biofuels (bioethanol, higher-alcohols, and biodiesel) were generated from carbohydrate-rich Chlamydomonas mexicana and lipid-rich Chlamydomonas pitschmannii biomass through energy-saving microwave pretreatment, successive fermentation, and transesterification. Microwave pretreatment needed low specific energy (4.2 MJ/kg) for 100 g/L of microalgal suspension. Proposed sustainable integrated pretreatments method achieved unprecedented total conversion efficiency (67%) and highest biomass utilization (87%) of C. pitschmannii (100 g/L) with high yields of bioethanol (0.48 g-ethanol/g-carbohydrates), higher-alcohols (0.44 g-higher-alcohols/g-proteins), and biodiesel (0.90 g-biodiesel/g-lipids). Transmission electron microscopy showed the changes in the microalgal cellular integrity before and after sequential fermentations. Energy-efficient integrated pretreatments enhanced the extraction efficiency and whole utilization of high-concentration microalgae to generate high-titer biofuels with minimum waste production.

Production of Succinic Acid from Amino Acids in Escherichia coli

Glutamate (Glu) and aspartate (Asp) are the most abundant amino acids in various sources of protein waste, recognized as a sustainable resource. In this study, Escherichia coli was engineered to produce succinic acid (SA) from Glu and Asp. Succinate dehydrogenase involved in the tricarboxylic acid was inactivated in the Glu-utilizing strain. To grow on Asp, this mutant strain was subjected to metabolic evolution. One resulting strain capable of metabolizing Asp was further evolved to improve the growth of Glu and Asp. After the deletion of arcA, the resulting strain was employed for the aerobic production of SA. The shake-flask culture was conducted with the minimal medium containing 10 g/L Glu and 10 g/L Asp. Finally, it resulted in the SA production, with a titer, the molar yield, and productivity reaching 72.8 mM (i.e., 8.6 g/L), 0.54 (ca. 75.4% of the theoretical yield), and 0.66 g/L/h, respectively. Overall, this study opens up a new avenue of the biorefinery platform based on renewable amino acids.

Waste biorefinery towards a sustainable circular bioeconomy: a solution to global issues

Global issues such as environmental problems and food security are currently of concern to all of us. Circular bioeconomy is a promising approach towards resolving these global issues. The production of bioenergy and biomaterials can sustain the energy-environment nexus as well as substitute the devoid of petroleum as the production feedstock, thereby contributing to a cleaner and low carbon environment. In addition, assimilation of waste into bioprocesses for the production of useful products and metabolites lead towards a sustainable circular bioeconomy. This review aims to highlight the waste biorefinery as a sustainable bio-based circular economy, and, therefore, promoting a greener environment. Several case studies on the bioprocesses utilising waste for biopolymers and bio-lipids production as well as bioprocesses incorporated with wastewater treatment are well discussed. The strategy of waste biorefinery integrated with circular bioeconomy in the perspectives of unravelling the global issues can help to tackle carbon management and greenhouse gas emissions. A waste biorefinery-circular bioeconomy strategy represents a low carbon economy by reducing greenhouse gases footprint, and holds great prospects for a sustainable and greener world.

A Strategy to Improve Production of Recombinant Proteins in Escherichia coli Based on a Glucose-Glycerol Mixture and Glutamate

Enzymes have a wide range of applications in many sectors of the industry, and the market value has skyrocketed in recent years. Glucose and glycerol are two renewable carbon sources of importance. Therefore, it is appealing to produce recombinant enzymes with these carbon substrates on the basis of economic viability. In this study, glycerol metabolism and glucose metabolism in Escherichia coli (E. coli) were manipulated in a systematic way. In addition, glutamate (Glu) was used for replacement of yeast extract to reduce the cost and the quality-variation problem. A strategy was further developed to incorporate Glu into the central metabolism. The engineered E. coli strain finally enabled efficient co-utilization of glucose and glycerol and improved biomass and protein production by 4.3 and 8.2-folds, respectively. The result illustrates that this proposed approach is promising for effective production of recombinant proteins.

Bacterial synthesis of C3-C5 diols via extending amino acid catabolism

Amino acids are naturally occurring and structurally diverse metabolites in biological system, whose potentials for chemical expansion, however, have not been fully explored. Here, we devise a metabolic platform capable of producing industrially important C3-C5 diols from amino acids. The presented platform combines the natural catabolism of charged amino acids with a catalytically efficient and thermodynamically favorable diol formation pathway, created by expanding the substrate scope of the carboxylic acid reductase toward noncognate ω-hydroxylic acids. Using the established platform as gateways, seven different diol-convertible amino acids are converted to diols including 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol. Particularly, we afford to optimize the production of 1,4-butanediol and demonstrate the de novo production of 1,5-pentanediol from glucose, with titers reaching 1.41 and 0.97 g l^-1, respectively. Our work presents a metabolic platform that enriches the pathway repertoire for nonnatural diols with feedstock flexibility to both sugar and protein hydrolysates.

The bacterial community and metabolome dynamics and their interactions modulate fermentation process of whole crop corn silage prepared with or without inoculants

Multi‐omics approach was adopted to investigate the modulation of bacterial microbiota and metabolome as well as their interactions in whole crop corn ensiling systems by inoculating homofermentative Lactobacillus plantarum or heterofermentative Lactobacillus buchneri. Inoculations of the two different inoculants resulted in substantial differences in microbial community and metabolic composition as well as their dynamics in ensiled corn. Inoculants also altered the correlations of microbiota in different manners, and various keystone species were identified in corn silages with different treatments. Many metabolites with biofunctional activities like bacteriostatic, antioxidant, central nervous system inhibitory and anti‐inflammatory were found in the present silage. A constitutive difference in microbiota dynamics was found for several pathways, which were upregulated by specific taxa in middle stage of fermentation, and widespread associations between metabolites with biofunctions and the species of lactic acid bacteria dominated in silage were observed. Multiple microbial and metabolic structures and dynamics were correlated and affected the fermentation process of the corn ensiling systems. Results of the current study improve our understanding of the complicated biological process underlying silage fermentation and provide a framework to re‐evaluate silages with biofunctions, which may contribute to target‐based regulation methods to produce functional silage for animal production.

Single and Mixed Feedstocks Biorefining: Comparison of Primary Metabolites Recovery and Lignin Recombination During an Alkaline Process

Cannabis sp. and Euphorbia sp. are potential candidates as indoor culture for the extraction of their high value-added metabolites for pharmaceutical applications. Both residual lignocellulosic materials recovered after extraction are studied in the present article as single or mixed feedstocks for a closed-loop bioprocesses cascade. An alkaline process (NaOH 3%, 30 min 160°C) is performed to separate the studied biomasses into their main components: lignin and cellulose. Results highlight the advantages of the multi-feedstocks approach over the single biomass in term of lignin yield and purity. Since the structural characteristics of lignin affect the potential applications, a particular attention is drawn on the comprehension of lignin structure alteration and the possible interaction between them during single or mixed feedstocks treatment. FTIR and 2D-NMR spectra revealed similar profiles in term of chemical functions and structure rather than novel chemical bonds formation inexistent in the original biomasses. In addition, thermal properties and molecular mass distribution are conserved whether hemp or euphorbia are single treated or in combination. A second treatment was applied to investigate the effect of prolonged treatment on extracted lignins and the possible interactions. Aggregation, resulting in higher molecular mass, is observed whatever the feedstocks combination. However, mixing biomass does not affect chemical structures of the end product. Therefore, our paper suggests the possibility of gathering lignocellulosic residues during alkali process for lignin extraction and valorization, allowing to forecast lignin structure and make assumptions regarding potential valorization pathway.

Wax ester production in nitrogen-rich conditions by metabolically engineered Acinetobacter baylyi ADP1

Metabolic engineering can be used as a powerful tool to redirect cell resources towards product synthesis, also in conditions that are not optimal for the production. An example of synthesis strongly dependent on external conditions is the production of storage lipids, which typically requires a high carbon/nitrogen ratio. This requirement also limits the use of abundant nitrogen-rich materials, such as industrial protein by-products, as substrates for lipid production. Acinetobacter baylyi ADP1 is known for its ability to produce industrially interesting storage lipids, namely wax esters (WEs). Here, we engineered A. baylyi ADP1 by deleting the gene aceA encoding for isocitrate lyase and overexpressing fatty acyl-CoA reductase Acr1 in the wax ester production pathway to allow redirection of carbon towards WEs. This strategy led to 3-fold improvement in yield (0.075 ​g/g glucose) and 3.15-fold improvement in titer (1.82 ​g/L) and productivity (0.038 ​g/L/h) by a simple one-stage batch cultivation with glucose as carbon source. The engineered strain accumulated up to 27% WEs of cell dry weight. The titer and cellular WE content are the highest reported to date among microbes. We further showed that the engineering strategy alleviated the inherent requirement for high carbon/nitrogen ratio and demonstrated the production of wax esters using nitrogen-rich substrates including casamino acids, yeast extract, and baker's yeast hydrolysate, which support biomass production but not WE production in wild-type cells. The study demonstrates the power of metabolic engineering in overcoming natural limitations in the production of storage lipids.

Synthesis of Diaryl Hydroxyl Dicarboxylic Acids from Amino Acids

Herein we report a unique method for preparing diaryl hydroxyl dicarboxylic acids in a diastereospecific manner. The three-component reaction occurs between amino acid, aromatic aldehyde, and primary alcohol in alkaline solutions under microwave-assisted conditions. The dicarboxylic acids are isolated as sodium salts in high yields (up to 77%) by direct precipitation from the reaction solution. The experimental results suggest that the diastereospecificity originates from a [3,3]-sigmatropic rearrangement followed by a sodium-assisted hydride transfer. As further shown, the previously unreported dicarboxylic acids are easily turned into corresponding δ-lactones.

Utilization of Amino Acid-Rich Wastes for Microbial Lipid Production

To produce microbial lipids for biofuel production, carbohydrates and related compounds from biomass have been routinely utilized, yet amino acids (AA) from protein-rich wastes have been overlooked so far. We use the oleaginous yeast Cryptococcus curvatus ATCC 20509 as a lipid producer and evaluate the capacity for lipid production on proteinogenic AA individually or in designated blends under two-staged culture conditions. It was found that cellular lipid contents reached 48.8%, 44.5% and 29.0% when yeast cells were cultivated in media-contained AA blends with compositional profiles similar to those of sheep viscera, meat industry by-products and fish muscle, respectively, and that lipid coefficients were more than 0.10 g g^-1. Furthermore, cellular lipid contents were higher than 20% when most AA were used individually. High lipid coefficients of over 0.23 g g^-1 were observed when Pro, Trp or Leu were used as a substrate. Results also indicated that higher initial media pH or reduced phosphate concentration was beneficial for lipid production on AA. This work demonstrated the potential to use AA and related wastes as substrates for microbial lipid production by the yeast C. curvatus, which fit well with the protein-based biorefinery concept. Further efforts should be devoted to recognizing the metabolic features, identifying more robust lipid producer and optimizing lipid production processes.

Biorefineries in circular bioeconomy: A comprehensive review

Biorefinery is a sustainable means of generating multiple bioenergy products from various biomass feedstocks through the incorporation of relevant conversion technologies. With the increased attention of circular economy in the past half-decade with the emphasis of holistically addressing economic, environmental, and social aspects of the industrial-sector, biorefinery acts as a strategic mechanism for the realization of a circular bioeconomy. This study presents a comprehensive review of different biorefinery models used for various biomass feedstocks such as lignocelluloses, algae, and numerous waste-types. The review focuses on how biorefinery is instrumental in the transition of various biomass-based industries in a circular bioeconomy. The results reveal that the social-economic aspect of the industrial sector has a major influence on the full adoption of biorefineries in circular bioeconomy. Biomass wastes have played a major role in the implementation of biorefinery in circular bioeconomy. The current challenges are also presented along with future perspectives.

Protein-based biorefining driven by nitrogen-responsive transcriptional machinery

BACKGROUND

Protein-based bioconversion has been demonstrated as a sustainable approach to produce higher alcohols and ammonia fertilizers. However, owing to the switchover from transcription mediated by the bacterial RNA polymerase σ⁷⁰ to that mediated by alternative σ factors, the biofuel production driven by σ⁷⁰-dependent promoters declines rapidly once cells enter the stationary phase or encounter stresses. To enhance biofuel production, in this study the growth phase-independent and nitrogen-responsive transcriptional machinery mediated by the σ⁵⁴ is exploited to drive robust protein-to-fuel conversion.

RESULTS

We demonstrated that disrupting the Escherichia coli ammonia assimilation pathways driven by glutamate dehydrogenase and glutamine synthetase could sustain the activity of σ⁵⁴-mediated transcription under ammonia-accumulating conditions. In addition, two σ⁵⁴-dependent promoters, argTp and glnAp2, were identified as suitable candidates for driving pathway expression. Using these promoters, biofuel production from proteins was shown to persist to the stationary phase, with the net production in the stationary phase being 1.7-fold higher than that derived from the optimal reported σ⁷⁰-dependent promoter P _LlacO₁. Biofuel production reaching levels 1.3- to 3.4-fold higher than those of the σ⁷⁰-dependent promoters was also achieved by argTp and glnAp2 under stressed conditions. Moreover, the σ⁵⁴-dependent promoters realized more rapid and stable production than that of σ⁷⁰-dependent promoters during fed-batch fermentation, producing up to 4.78 g L ^- 1 of total biofuels.

CONCLUSIONS

These results suggested that the nitrogen-responsive transcriptional machinery offers the potential to decouple production from growth, highlighting this system as a novel candidate to realize growth phase-independent and stress-resistant biofuel production.

Biotransformation of green tea (Camellia sinensis) by wine yeast Saccharomyces cerevisiae

Wine yeast Saccharomyces cerevisiae 71B was used in fermentation of green tea to modulate the volatiles and nonvolatiles. After fermentation, higher alcohols, esters, and acids, such as isoamyl alcohol, isobutanol, ethyl octanoate, ethyl decanoate, octanoic, and decanoic acids were generated. Some key aroma compounds of tea including linalool, hotrienol, dihydroactinidiolide, and 2-phenylethanol increased significantly. Among these compounds, linalool and 2-phenylethanol increased by 1.3- and 10-fold, respectively, which impart floral and fruity notes to fermented green tea. Alkaloids including caffeine, theobromine, and theophylline were reduced significantly after fermentation, while the most important free amino acid in tea, theanine, was not metabolized by S. cerevisiae. Tea catechins decreased whereas gallic and caffeic acids increased significantly, resulting in the unchanged antioxidant capacity of the fermented green tea. Hence, this work highlighted the potential of using S. cerevisiae to modulate green tea aroma and nonvolatiles. PRACTICAL APPLICATION: A novel fermented tea is produced by yeast fermentation. Saccharomyces cerevisiae led to significant changes in tea volatiles and nonvolatiles. Antioxidant capacity remained stable after fermentation.

Challenges and opportunity of recent genome editing and multi-omics in cyanobacteria and microalgae for biorefinery

Microalgae and cyanobacteria are easy to culture, with higher growth rates and photosynthetic efficiencies compared to terrestrial plants, and thus generating higher productivity. The concept of microalgal biorefinery is to assimilate carbon dioxide and convert it to chemical energy/value-added products, such as vitamins, carotenoids, fatty acids, proteins and nucleic acids, to be applied in bioenergy, health foods, aquaculture feed, pharmaceutical and medical fields. Therefore, microalgae are annotated as the third generation feedstock in bioenergy and biorefinery. In past decades, many studies thrived to improve the carbon sequestration efficiency as well as enhance value-added compounds from different algae, especially via genetic engineering, synthetic biology, metabolic design and regulation. From the traditional Agrobacterium-mediated transformation DNA to novel CRISPR (clustered regularly interspaced short palindromic repeats) technology applied in microalgae and cyanobacteria, this review has highlighted the genome editing technology for biorefinery that is a highly environmental friendly trend to sustainable and renewable development.

Development of CRISPR/Cas9 system in Chlorella vulgaris FSP-E to enhance lipid accumulation

Microalgae biorefinery is an alternative, sustainable and promising trend to solve the problem of fossil oil depletion and carbon dioxide emission. However, considering the innate limitation of cell growth and oil content in microalgae, to accelerate metabolic balance by CRISPR/Cas9 system is attractive. At first, plasmid based from Agrobacterium tumefaciens and a fragment of mGFP was transformed into Chlorella sorokiniana and Chlorella vulgaris FSP-E by electroporation, respectively. Selected colonies were tested by spectrophotometer and inverted fluorescence microscopy (IFM), and an increase of fluorescent was observed by 67% compared with that in wild type, which proved the Agrobacterium-mediated plasmid is suitable for gene insertion in Chlorella species. Consequently, plasmid with similar structure as mentioned previously containing fragment of Cas9 with sgRNA designed on omega-3 fatty acid desaturase (fad3) gene was constructed and showed a higher accumulation of lipid content by 46% (w/w) in C. vulgaris FSP-E. This is first-time to use CRISPR/Cas9 based technology for gene manipulation in Chlorella.