Sustainability of biofuels and renewable chemicals production from biomass

A Comparison of Dilute Aqueous Isethionic Acid and Sulfuric Acid in Hydrolysis of Three Different Untreated Lignocellulosic Biomass Varieties

Efficient catalytic hydrolysis of lignocellulosic biomass to sugars is a major challenge in the production of sustainable biofuels and chemical feedstocks. In this study isethionic acid was compared with H2SO4 for hydrolysis of polysaccharides in corn stover, switch grass, and poplar. The catalytic activities of acids were compared by analysis of total reducing sugar (TRS) and glucose yields in a sequence of experiments in water at 90-190 °C using 0.050 mol of H+/L isethionic acid and H2SO4. In comparison to using H2SO4, the use of isethionic acid catalyst lowered the maximum TRS percent yield temperatures by 25, 24, and 21% for corn stover, switch grass, and poplar. A similar effect was observed for glucose percent yields as well. This temperature reduction is due to lowering of the activation energy in the polysaccharide depolymerization reaction and most likely due to hydrogen-bonding-type dipolar interactions between the isethionic acid -OH group and -OH groups in biomass polysaccharides.

Cyanobacteria-Mediated Light-Driven Biotransformation: The Current Status and Perspectives

Most chemicals are manufactured by traditional chemical processes but at the expense of toxic catalyst use, high energy consumption, and waste generation. Biotransformation is a green, sustainable, and cost-effective process. As cyanobacteria can use light as the energy source to power the synthesis of NADPH and ATP, using cyanobacteria as the chassis organisms to design and develop light-driven biotransformation platforms for chemical synthesis has been gaining attention, since it can provide a theoretical and practical basis for the sustainable and green production of chemicals. Meanwhile, metabolic engineering and genome editing techniques have tremendous prospects for further engineering and optimizing chassis cells to achieve efficient light-driven systems for synthesizing various chemicals. Here, we display the potential of cyanobacteria as a promising light-driven biotransformation platform for the efficient synthesis of green chemicals and current achievements of light-driven biotransformation processes in wild-type or genetically modified cyanobacteria. Meanwhile, future perspectives of one-pot enzymatic cascade biotransformation from biobased materials in cyanobacteria have been proposed, which could provide additional research insights for green biotransformation and accelerate the advancement of biomanufacturing industries.

The current situations and limitations of genetic engineering in cyanobacteria: a mini review

Cyanobacteria are an ancient group of photoautotrophic prokaryotes, and play an essential role in the global carbon cycle. They are also model organisms for studying photosynthesis and circadian regulation, and metabolic engineering and synthetic biology strategies grants light-driven biotechnological applications to cyanobacteria, especially for engineering cyanobacteria cells to achieve an efficient light-driven system for synthesizing any product of interest from renewable feedstocks. However, lower yield limits the potential of industrial application of cyanobacterial synthetic biology, and some key limitations must be overcome to realize the full biotechnological potential of these versatile microorganisms. Although genetic engineering toolkits for cyanobacteria have made some progress, the tools available still lag behind conventional heterotrophic microorganism. Consequently, this study describes the current situations and limitations of genetic engineering in cyanobacteria, and further improvements are proposed to improve the output of targeted products. We believe that cyanobacteria-mediated light-driven platforms towards efficient synthesis of green chemicals could unlock a bright future by developing the tools for strain manipulation and novel chassis organisms with excellent performance for biotechnological applications, which could also accelerate the advancement of bio-manufacturing industries.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Enzymatic Conversion of CO2: From Natural to Artificial Utilization

Enzymatic carbon dioxide fixation is one of the most important metabolic reactions as it allows the capture of inorganic carbon from the atmosphere and its conversion into organic biomass. However, due to the often unfavorable thermodynamics and the difficulties associated with the utilization of CO₂, a gaseous substrate that is found in comparatively low concentrations in the atmosphere, such reactions remain challenging for biotechnological applications. Nature has tackled these problems by evolution of dedicated CO₂-fixing enzymes, i.e., carboxylases, and embedding them in complex metabolic pathways. Biotechnology employs such carboxylating and decarboxylating enzymes for the carboxylation of aromatic and aliphatic substrates either by embedding them into more complex reaction cascades or by shifting the reaction equilibrium via reaction engineering. This review aims to provide an overview of natural CO₂-fixing enzymes and their mechanistic similarities. We also discuss biocatalytic applications of carboxylases and decarboxylases for the synthesis of valuable products and provide a separate summary of strategies to improve the efficiency of such processes. We briefly summarize natural CO₂ fixation pathways, provide a roadmap for the design and implementation of artificial carbon fixation pathways, and highlight examples of biocatalytic cascades involving carboxylases. Additionally, we suggest that biochemical utilization of reduced CO₂ derivates, such as formate or methanol, represents a suitable alternative to direct use of CO₂ and provide several examples. Our discussion closes with a techno-economic perspective on enzymatic CO₂ fixation and its potential to reduce CO₂ emissions.

Development of shuttle vectors for rapid prototyping of engineered Synechococcus sp. PCC7002

Cyanobacteria are of particular interest for chemical production as they can assimilate CO₂ and use solar energy to power chemical synthesis. However, unlike the model microorganism of Escherichia coli, the availability of genetic toolboxes for rapid proof-of-concept studies in cyanobacteria is generally lacking. In this study, we first characterized a set of promoters to efficiently drive gene expressions in the marine cyanobacterium Synechococcus sp. PCC7002. We identified that the endogenous cpcBA promoter represented one of the strongest promoters in PCC7002. Next, a set of shuttle vectors was constructed based on the endogenous pAQ1 plasmid to facilitate the rapid pathway assembly. Moreover, we used the shuttle vectors to modularly optimize the amorpha-4,11-diene synthesis in PCC7002. By modularly optimizing the metabolic pathway, we managed to redistribute the central metabolism toward the amorpha-4,11-diene production in PCC7002 with enhanced product titer. Taken together, the plasmid toolbox developed in this study will greatly accelerate the generation of genetically engineered PCC7002. KEY POINTS: • Promoter characterization revealed that the endogenous cpcBA promoter represented one of the strongest promoters in PCC7002 • A set of shuttle vectors with different antibiotic selection markers was constructed based on endogenous pAQ1 plasmid • By modularly optimizing the metabolic pathway, amorpha-4,11-diene production in PCC7002 was improved.

Microbial production of advanced biofuels

Concerns over climate change have necessitated a rethinking of our transportation infrastructure. One possible alternative to carbon-polluting fossil fuels is biofuels produced by engineered microorganisms that use a renewable carbon source. Two biofuels, ethanol and biodiesel, have made inroads in displacing petroleum-based fuels, but their uptake has been limited by the amounts that can be used in conventional engines and by their cost. Advanced biofuels that mimic petroleum-based fuels are not limited by the amounts that can be used in existing transportation infrastructure but have had limited uptake due to costs. In this Review, we discuss engineering metabolic pathways to produce advanced biofuels, challenges with substrate and product toxicity with regard to host microorganisms and methods to engineer tolerance, and the use of functional genomics and machine learning approaches to produce advanced biofuels and prospects for reducing their costs.

Omics analysis reveals mechanism underlying metabolic oscillation during continuous very-high-gravity ethanol fermentation by Saccharomyces cerevisiae

During continuous very-high-gravity (VHG) ethanol fermentation with Saccharomyces cerevisiae, the process exhibits sustained oscillation in residual glucose, ethanol, and biomass, raising a question: how do yeast cells respond to this phenomenon? In this study, the oscillatory behavior of yeast cells was characterized through transcriptome and metabolome analysis for one complete oscillatory period. By analyzing the accumulation of 26 intracellular metabolites and the expression of 90 genes related to central carbon metabolism and stress response, we confirmed that the process oscillation was attributed to intracellular metabolic oscillation with phase difference, and the expression of HXK1, HXT1,2,4, and PFK1 was significantly different from other genes in the Embden-Meyerhof-Parnas pathway, indicating that glucose transport and phosphorylation could be key nodes for regulating the intracellular metabolism under oscillatory conditions. Moreover, the expression of stress response genes was triggered and affected predominately by ethanol inhibition in yeast cells. This progress not only contributes to the understanding of mechanisms underlying the process oscillation observed for continuous VHG ethanol fermentation, but also provides insights for understanding unsteady state that might develop in other continuous fermentation processes operated under VHG conditions to increase product titers for robust production.

High-level expression of a novel multifunctional GH3 family β-xylosidase/α-arabinosidase/β-glucosidase from Dictyoglomus turgidum in Escherichia coli

A novel β-xylosidase Dt-2286 from Dictyoglomus turgidum was cloned and overexpressed in Escherichia coli BL21 (DE3). Dt-2286 belonging to glycoside hydrolase (GH) family 3 encodes a polypeptide with 762 amino acid residues with a molecular weight of 85.1 kDa. By optimization of the growth and induction conditions, the activity of β-xylosidase reached 273 U/mL, which is the highest yield reported to date from E. coli in a shake-flask. The optimal activities of the purified Dt-2286 were found at pH 5.0 and 98 °C. It also shows excellent thermostable/haloduric/organic solvent-tolerance. Dt-2286 was revealed to be a multifunctional enzyme with β-xylosidase, α-arabinofuranoside, α-arabinopyranoside and β-glucosidase activities, and K_cat/K_m was 5245.316 mM^-1 s^-1, 2077.353 mM^-1 s^-1, 1626.454 mM^-1 s^-1, and 470.432 mM^-1 s^-1 respectively. Dt-2286 showed significant synergistic effects on the degradation of xylans, releasing more reduced sugars (up to 15.08 fold) by simultaneous addition with endoxylanase. Moreover, this enzyme has good activity in the hydrolysis of epimedium B, demonstrating its versatility in practical applications.

Review on integrated biofuel production from microalgal biomass through the outset of transesterification route: a cascade approach for sustainable bioenergy

In recent years, microalgal feedstocks have gained immense potential for sustainable biofuel production. Thermochemical, biochemical conversions and transesterification processes are employed for biofuel production. Especially, the transesterification process of lipid molecules to fatty acid alkyl esters (FAAE) is being widely employed for biodiesel production. In the case of the extractive transesterification process, biodiesel is produced from the extracted microalgal oil. Whereas In-situ (reactive) transesterification allows the direct conversion of microalgae to biodiesel avoiding the sequential steps, which subsequently reduces the production cost. Though microalgae have the highest potential to be an alternate renewable feedstock, the minimization of biofuel production cost is still a challenge. The biorefinery approaches that rely on simple cascade processes involving cost-effective technologies are the need of an hour for sustainable bioenergy production using microalgae. At the same time, combining the biorefineries for both (i) high value-low volume (food and health supplements) and (ii) low value- high volume (waste remediation, bioenergy) from microalgae involves regulatory and technical problems. Waste-remediation and algal biorefinery were extensively reviewed in many previous reports. On the other hand, this review focuses on the cascade processes for efficient utilization of microalgae for integrated bioenergy production through the transesterification. Microalgal biomass remnants after the transesterification process, comprising carbohydrates as a major component (process flow A) or the carbohydrate fraction after bio-separation of pretreated microalgae (process flow B) can be utilized for bioethanol production. Therefore, this review concentrates on the cascade flow of integrated bioprocessing methods for biodiesel and bioethanol production through the transesterification and biochemical routes. The review also sheds light on the recent combinatorial approaches of transesterification of microalgae. The applicability of spent microalgal biomass residue for biogas and other applications to bring about zero-waste residue are discussed. Furthermore, techno-economic analysis (TEA), life cycle assessment (LCA) and challenges of microalgal biorefineries are discussed.

Socio-Economic and Environmental Impacts of Biomass Valorisation: A Strategic Drive for Sustainable Bioeconomy

In the late twentieth century, the only cost-effective opportunity for waste removal cost at least several thousand dollars, but nowadays, a lot of improvement has occurred. The biomass and waste generation problems attracted concerned authorities to identify and provide environmentally friendly sustainable solutions that possess environmental and economic benefits. The present study emphasises the valorisation of biomass and waste produced by domestic and industrial sectors. Therefore, substantial research is ongoing to replace the traditional treatment methods that potentially acquire less detrimental effects. Synthetic biology can be a unique platform that invites all the relevant characters for designing and assembling an efficient program that could be useful to handle the increasing threat for human beings. In the future, these engineered methods will not only revolutionise our lives but practically lead us to get cheaper biofuels, producing bioenergy, pharmaceutics, and various biochemicals. The bioaugmentation approach concomitant with microbial fuel cells (MFC) is an example that is used to produce electricity from municipal waste, which is directly associated with the loading of waste. Beyond the traditional opportunities, herein, we have spotlighted the new advances in pertinent technology closely related to production and reduction approaches. Various integrated modern techniques and aspects related to the industrial sector are also discussed with suitable examples, including green energy and other industrially relevant products. However, many problems persist in present-day technology that requires essential efforts to handle thoroughly because significant valorisation of biomass and waste involves integrated methods for timely detection, classification, and separation. We reviewed and proposed the anticipated dispensation methods to overcome the growing stream of biomass and waste at a distinct and organisational scale.

Efficient Production of 1,3-Propanediol from Diverse Carbohydrates via a Non-natural Pathway Using 3-Hydroxypropionic Acid as an Intermediate

1,3-Propanediol (1,3-PDO) is a promising platform chemical used to manufacture various polyesters, polyethers, and polyurethanes. Microbial production of 1,3-PDO using non-natural producers often requires adding expensive cofactors such as vitamin B₁₂, which increases the whole production cost. In this study, we proposed and engineered a non-natural 1,3-PDO synthetic pathway derived from acetyl-CoA, enabling efficient accumulation of 1,3-PDO in Escherichia coli without adding expensive cofactors. This functional pathway was established by introducing the malonyl-CoA-dependent 3-hydroxypropionic acid (3-HP) module and screening the key enzymes to convert 3-HP to 1,3-PDO. The best engineered strain can produce 2.93 g/L 1,3-PDO with a yield of 0.35 mol/mol glucose in shake flask cultivation (and 7.98 g/L in fed-batch fermentation), which is significantly higher than previous reports based on homoserine- or malate-derived non-natural pathways. We also demonstrated for the first time the feasibility of producing 1,3-PDO from diverse carbohydrates including xylose, glycerol, and acetate based on the same pathway. Thus, this study provides an alternative route for 1,3-PDO production.

Symbiont-Mediated Digestion of Plant Biomass in Fungus-Farming Insects

Feeding on living or dead plant material is widespread in insects. Seminal work on termites and aphids has provided profound insights into the critical nutritional role that microbes play in plant-feeding insects. Some ants, beetles, and termites, among others, have evolved the ability to use microbes to gain indirect access to plant substrate through the farming of a fungus on which they feed. Recent genomic studies, including studies of insect hosts and fungal and bacterial symbionts, as well as metagenomics and proteomics, have provided important insights into plant biomass digestion across insect-fungal mutualisms. Not only do advances in understanding of the divergent and complementary functions of complex symbionts reveal the mechanism of how these herbivorous insects catabolize plant biomass, but these symbionts also represent a promising reservoir for novel carbohydrate-active enzyme discovery, which is of considerable biotechnological interest.

Life Cycle Assessment Analysis of Alfalfa and Corn for Biogas Production in a Farm Case Study

In the last years the greenhouse effect has been significantly intensified due to human activities, generating large additional amounts of Greenhouse gases (GHG). The fossil fuels are the main causes of that. Consequently, the attention on the composition of the national fuel mix has significantly grown, and the renewables are becoming a more significant component. In this context, biomass is one of the most important sources of renewable energy with a great potential for the production of energy. The study has evaluated, through an LCA (Life Cycle Assessment) study, the attitude of alfalfa (Medicago sativa) as “no food” biomass alternative to maize silage (corn), in the production of biogas from anaerobic digestion. Considering the same functional unit (1 m3 of biogas from anaerobic digestion) and the same time horizon, alfalfa environmental impact was found to be much comparable to that of corn because it has an impact of about 15% higher than corn considering the total score from different categories and an impact of 5% higher of corn considering only greenhouse gases. Therefore, the analysis shows a similar environmental load in the use of alfalfa biomass in energy production compared to maize. Corn in fact, despite a better yield per hectare and yield of biogas, requires a greater amount of energy inputs to produce 1m3 of biogas, while alfalfa, which requires less energy inputs in its life cycle, has a lower performance in terms of yield. The results show the possibility to alternate the two crops for energy production from an environmental perspective.

Construction of engineered yeast producing ammonia from glutamine and soybean residues (okara)

Ammonia is an essential substance for agriculture and the chemical industry. The intracellular production of ammonia in yeast (Saccharomyces cerevisiae) by metabolic engineering is difficult because yeast strongly assimilates ammonia, and the knockout of genes enabling this assimilation is lethal. Therefore, we attempted to produce ammonia outside the yeast cells by displaying a glutaminase (YbaS) from Escherichia coli on the yeast cell surface. YbaS-displaying yeast successfully produced 3.34 g/L ammonia from 32.6 g/L glutamine (83.2% conversion rate), providing it at a higher yield than in previous studies. Next, using YbaS-displaying yeast, we also succeeded in producing ammonia from glutamine in soybean residues (okara) produced as food waste from tofu production. Therefore, ammonia production outside cells by displaying ammonia-lyase on the cell surface is a promising strategy for producing ammonia from food waste as a novel energy resource, thereby preventing food loss.

Developing Process Designs for Biorefineries—Definitions, Categories, and Unit Operations

In this review, we focus on the literature that described the various unit operations in a process design flowsheet of biorefineries. We begin by establishing the accepted definitions of a biorefinery, go on to describe how to categorize biorefineries, and finally review the literature on biorefinery process designs by listing the unit operation in each process design. Distinguishing biorefineries based on feedstock, the types of processing units, and the products emanating from the biorefinery are discussed.

Genetically Engineered Proteins to Improve Biomass Conversion: New Advances and Challenges for Tailoring Biocatalysts

Protein engineering emerged as a powerful approach to generate more robust and efficient biocatalysts for bio-based economy applications, an alternative to ecologically toxic chemistries that rely on petroleum. On the quest for environmentally friendly technologies, sustainable and low-cost resources such as lignocellulosic plant-derived biomass are being used for the production of biofuels and fine chemicals. Since most of the enzymes used in the biorefinery industry act in suboptimal conditions, modification of their catalytic properties through protein rational design and in vitro evolution techniques allows the improvement of enzymatic parameters such as specificity, activity, efficiency, secretability, and stability, leading to better yields in the production lines. This review focuses on the current application of protein engineering techniques for improving the catalytic performance of enzymes used to break down lignocellulosic polymers. We discuss the use of both classical and modern methods reported in the literature in the last five years that allowed the boosting of biocatalysts for biomass degradation.

Bioeconomy: Markets, Implications, and Investment Opportunities

In order to achieve the objectives of the Paris Climate Change Agreement, the conversion of our economy, which is still dominated by fossil carbon, to the bioeconomy model must be completed by 2050. This requires a shift from oil, gas and coal to agricultural, forestry and marine raw materials and will affect the global processing chains for energy, fuels and chemicals. However, the land required for the production of raw materials is competing with the production of food and animal feed. In addition, future land use must better take into account planetary boundaries and the preservation of ecosystem services. In order to achieve economic, ecological and societal sustainability, the necessary measures must therefore be geared towards the UN’s sustainability goals. Against this background, the future bioeconomy will have to concentrate on the food, chemical and heavy fuel sectors. Important sub-areas are alternative animal protein for nutrition, feedstock efficiency in the processing of bio-based raw materials, and the expansion of the raw materials spectrum. This requires enormous investment in industrial facilities, the integration of newly emerging value chains and the necessary infrastructure. The annual global investment requirements for renewable energy, bio-based chemicals and fuels, and ecosystem services is estimated at USD 1–2 trillion over the next three decades, equivalent to about 1.3–2.6% of global GDP. This article discusses the implications and guard rails of the bioeconomy model, as well as capital needs and possible sources.

Low-Carbon Futures for Bioethylene in the United States

The manufacture of the chemical ethylene, a key ingredient in plastics, currently depends on fossil-fuel-derived carbon and generates significant greenhouse gas emissions. Substituting ethylene’s fossil fuel feedstock with alternatives is important for addressing the challenge of global climate change. This paper compares four scenarios for meeting future ethylene supply under differing societal approaches to climate change based on the Shared Socioeconomic Pathways. The four scenarios use four perspectives: (1) a sustainability-focused pathway that demands a swift transition to a bioeconomy within 30 years; (2) a regional energy-focused pathway that supports broad biomass use; (3) a fossil-fuel development pathway limited to corn grain; and (4) a fossil-fuel development pathway limited to corn grain and corn stover. Each scenario is developed using the latest scientifically informed future feedstock analyses from the 2016 Billion-Ton report interpreted with perspectives on the future of biomass from recent literature. The intent of this research is to examine how social, economic, and ecological changes determining ethylene supply fit within biophysical boundaries. This new approach to the ethylene feedstocks conundrum finds that phasing out fossil fuels as the main source of U.S. ethylene is possible if current cellulosic ethanol production expands.

The art of vector engineering: towards the construction of next-generation genetic tools

When recombinant DNA technology was developed more than 40 years ago, no one could have imagined the impact it would have on both society and the scientific community. In the field of genetic engineering, the most important tool developed was the plasmid vector. This technology has been continuously expanding and undergoing adaptations. Here, we provide a detailed view following the evolution of vectors built throughout the years destined to study microorganisms and their peculiarities, including those whose genomes can only be revealed through metagenomics. We remark how synthetic biology became a turning point in designing these genetic tools to create meaningful innovations. We have placed special focus on the tools for engineering bacteria and fungi (both yeast and filamentous fungi) and those available to construct metagenomic libraries. Based on this overview, future goals would include the development of modular vectors bearing standardized parts and orthogonally designed circuits, a task not fully addressed thus far. Finally, we present some challenges that should be overcome to enable the next generation of vector design and ways to address it.

Sustainable Supply Chain and Innovation: A Review of the Recent Literature

Increasingly, the effects of supply chains on environmental issues have been a focal point in discussions involving stakeholders, authorities, and customers. The aim of this paper is to inspect how innovation and sustainability are integrated into the wider context of the supply chains. To this end, a systematic literature review was carried out with a particular focus on papers published in recent years (2015–2017) so as to continue from a previous review on the sustainable supply chain innovation topic covering the time span of 1996–2014. The descriptive aspects of the published papers are firstly examined, i.e., the year of publication, journal, research methodology, industry field and country of the study, followed by the thematic ones, i.e., key themes of the innovation process, the types of innovation found, their newness, dimensions, and main theories that emerged. The analysis shows an upward trend of literature in numerical terms and a wider spread of sustainable innovations. Additionally, the research highlights further areas of research that are deserving of attention. These areas include analyses of specific industrial sectors which have been less covered in the published literature; research activities in the less developed countries; more attention on the social dimension of sustainability; a more general contribution from some nations that turned out to be less productive or even inactive on the sustainable supply chain innovation topic. Finally, a framework is developed which could constitute the basis for further developments and research on this issue.

Efficient production of 3-hydroxypropionate from fatty acids feedstock in Escherichia coli

The production of chemicals from renewable biomass resources is usually limited by factors including high-cost processes and low efficiency of biosynthetic pathways. Fatty acids (FAs) are an ideal alternative biomass. Their advantages include high-efficiently producing acetyl-CoA and reducing power, coupling chemical production with CO₂ fixation, and the fact that they are readily obtained from inexpensive feedstocks. The important platform chemical 3-hydroxypropionate (3HP) can be produced from FAs as the feedstock with a theoretical yield of 2.49 g/g, much higher than the theoretical yield from other feedstocks. In this study, we first systematically analyzed the limiting factors in FA-utilization pathways in Escherichia coli. Then, we optimized FA utilization in Escherichia coli by using a combination of metabolic engineering and optimization of fermentation conditions. The 3HP biosynthesis module was introduced into a FA-utilizing strain, and the flux balance was finely optimized to maximize 3HP production. The resulting strain was able to produce 3HP from FAs with a yield of 1.56 g/g, and was able to produce 3HP to a concentration of 52 g/L from FAs in a 5-L fermentation process. The strain also could produce 3HP from various type of FAs feedstock including gutter oil. This is the first report of a technique for the efficient production of the platform chemical 3HP from FAs.

Biochemical characterization of Caulobacter crescentus xylose dehydrogenase

d-Xylose sugar is a common component of hemicellulose, the second largest fraction of biomass. Many groups have developed biological conversions of d-xylose to value-added products by recombinant expression of the xylose dehydrogenase enzyme from Caulobacter crescentus. This enzyme uses NAD⁺ as a cofactor to oxidize d-xylose to d-xylono-1,4-lactone. A detailed understanding of the mechanism of this enzyme could be useful in engineering more efficient versions. Therefore, we have conducted kinetic studies including both the forward and reverse physiological reactions of this enzyme. We demonstrate that the enzyme's substrate binding mode follows a sequential steady state ordered mechanism with NAD⁺ or NADH binding first. Furthermore, the k_cat of the reaction in the direction of NAD⁺ reduction is 10-fold higher than that of the reverse reaction. From rapid reaction studies, we demonstrate the binding of NAD⁺ and NADH to the free enzyme and that hydride transfer occurs in a fast step followed by a much slower steady state. We calculate that the dissociations of the sugar products from the enzyme complexes are the major rate limiting steps in both directions.

Non-plastidial expression of a synthetic insect geranyl pyrophosphate synthase effectively increases tobacco plant biomass

Designing effective synthetic genes of interest is a fundamental step in plant synthetic biology for biomass. Geranyl pyrophosphate (diphosphate) synthase (GPPS) catalyzes a bottleneck step toward terpenoid metabolism. We previously designed and synthesized a plant (Arabidopsis thaliana)-insect (Myzus persicae, Mp) GPPS- human influenza hemagglutinin (HA) cDNA, namely PTP-MpGPPS-HA (or PTP-sMpGPPS-HA, s: synthetic), to localize the protein in plastids and improve plant biomass. To better understand the effects of different subcellular localizations on plant performance, herein we report PTP-sMpGPPS-HA re-design to synthesize a new MpGPPS-HA cDNA, namely sMpGPPS-HA, to express a non-plastidial sMpGPPS-HA protein. The sMpGPPS-HA cDNA driven by a 2 × S 35S promoter was introduced into Nicotiana tabacum Xanthi. PTP-MpGPPS-HA and PMDC84 vector transgenic plants were also generated as positive and negative controls, respectively. Eighteen to twenty transgenic T0 lines were generated for each sMpGPPS-HA, PTP-sMpGPPS-HA, and PMDC84. Transcriptional genotyping analysis demonstrated the expression of sMpGPPS-HA in transgenic plants. Confocal microscopy analysis of transgenic progeny demonstrated the non-plastidial localization of sMpGPPS-HA. Growth of T1 transgenic and wild-type control plants showed that the expression of sMpGPPS-HA effectively increased plant height by 50-80%, leaf numbers and sizes, and dry biomass by 60-80%. Calculation of the vegetative growth rates showed that the expression of sMpGPPS-HA increased plant height each week. Moreover, sMpGPPS-HA expression promoted early flowering and reduced leaf carotenoid levels. In conclusion, non-plastidial expression of the novel sMpGPPS-HA was effective for improving tobacco growth and biomass. Our data indicate that research examining different subcellular localizations facilitates a better understanding of in planta functions of proteins encoded by synthetic cDNAs.

Cellulases: Role in Lignocellulosic Biomass Utilization

Rapid depletion of fossil fuels worldwide presents a dire situation demanding a potential replacement to surmount the current energy crisis. Lignocellulose presents a logical candidate to be exploited at industrial scale owing to its vast availability, inexpensive and renewable nature. Microbial degradation of lignocellulosic biomass is a lucrative, sustainable, and promising approach to obtain valuable commercial commodities at gigantic scale. The enzymatic hydrolysis involving cellulases is fundamental to all the technologies needed to transform lignocellulosic biomass to valuable industry relevant products. Cellulases have enormous potential to utilize cellulosic biomass, thus reducing environmental stress in addition to production of commodity chemicals resolving the current challenge to meet the energy needs globally. The substitution of petroleum-based fuels with bio-based fuels is the subject of thorough research establishing biofuel production as the future technology to achieve a sustainable, eco-friendly society with a zero waste approach.

Enzymatic hydrolysis of lignocellulosic biomass from low to high solids loading

Solid state enzymatic hydrolysis (SSEH) has many advantages, such as higher sugar concentration, lower operating costs, and less energy input. It should be a potential approach for the industrial application of lignocellulosic ethanol. The purpose of this work is to review the enzymatic hydrolysis of lignocellulosic biomass from low to high solids loading and introduce its both challenges and perspectives. The limitations of SSEH, including inhibition effects, water constraint, and rheology characteristic, are summarized firstly. Various strategies for overcoming these limitations are proposed correspondingly. Fed batch process and its feeding strategy to improve the SSEH efficiency are then discussed. Finally, several intensification methods, hydrolysis reactor, and pilot- and demonstration-scale operations of SSEH are described. In-depth analysis of main limitations and development of novel intensification methods and reactors should provide an effective way to achieve large-scale implementation of SSEH.

Fungal Enzymes for Bio-Products from Sustainable and Waste Biomass

Lignocellulose, the most abundant renewable carbon source on earth, is the logical candidate to replace fossil carbon as the major biofuel raw material. Nevertheless, the technologies needed to convert lignocellulose into soluble products that can then be utilized by the chemical or fuel industries face several challenges. Enzymatic hydrolysis is of major importance, and we review the progress made in fungal enzyme technology over the past few years with major emphasis on (i) the enzymes needed for the conversion of polysaccharides (cellulose and hemicellulose) into soluble products, (ii) the potential uses of lignin degradation products, and (iii) current progress and bottlenecks for the use of the soluble lignocellulose derivatives in emerging biorefineries.

Low-Carbon Fuel and Chemical Production by Anaerobic Gas Fermentation

World energy demand is expected to increase by up to 40% by 2035. Over this period, the global population is also expected to increase by a billion people. A challenge facing the global community is not only to increase the supply of fuel, but also to minimize fossil carbon emissions to safeguard the environment, at the same time as ensuring that food production and supply is not detrimentally impacted. Gas fermentation is a rapidly maturing technology which allows low carbon fuel and commodity chemical synthesis. Unlike traditional biofuel technologies, gas fermentation avoids the use of sugars, relying instead on gas streams rich in carbon monoxide and/or hydrogen and carbon dioxide as sources of carbon and energy for product synthesis by specialized bacteria collectively known as acetogens. Thus, gas fermentation enables access to a diverse array of novel, large volume, and globally available feedstocks including industrial waste gases and syngas produced, for example, via the gasification of municipal waste and biomass. Through the efforts of academic labs and early stage ventures, process scale-up challenges have been surmounted through the development of specialized bioreactors. Furthermore, tools for the genetic improvement of the acetogenic bacteria have been reported, paving the way for the production of a spectrum of ever-more valuable products via this process. As a result of these developments, interest in gas fermentation among both researchers and legislators has grown significantly in the past 5 years to the point that this approach is now considered amongst the mainstream of emerging technology solutions for near-term low-carbon fuel and chemical synthesis.