Biofuels for a sustainable future

Rapid increases of energy consumption and human dependency on fossil fuels have led to the accumulation greenhouse gases consequently, climate change. As such, major efforts been taken develop, test, adopt clean renewable fuel alternatives. Production bioethanol biodiesel from crops is well developed, while other feedstock resources processes also shown high potential provide efficient cost-effective alternatives, such as landfill plastic waste conversion, algal photosynthesis, electrochemical carbon fixation. In addition, downstream microbial fermentation can be further engineered not only increase product yield but expand chemical space biofuels through rational design fine-tuning biosynthetic pathways toward realization “designer fuels” diverse future applications. There a clear need transition dependence sources address unprecedented pace change due (GHGs) in atmosphere. Overwhelming evidence has that activity driver its consequences are impacting food production, migration patterns, economic, political stability global scale. US alone, 6.677 gigatons GHG were emitted 2018 with largest fractions being attributed transportation (28%), electricity generation (27%), industry (22%), commercial residential applications (12%), agriculture (10%) (US Environmental Protection Agency, 2020US AgencyInventory U.S. Greenhouse Gas Emissions Sinks.2020https://www.epa.gov/sites/production/files/2020-04/documents/us-ghg-inventory-2020-main-text.pdfGoogle Scholar). all these activities largely dependent fuels, technological advances diversification alternative hold promise significantly reduce emissions alleviate Predating use petroleum itself, vegetable oils, animal fats, ethanol used for heat illumination (Figure 1). This exemplified by first mass-produced car, Ford model T, which ran corn-derived ethanol. automobile production became increasingly industrialized early 20th century, it evident scheme could no longer meet ever-growing demand internal combustion engines. Today, environmental policies pushing reduction emission, aided recent crop engineering processes, once again become viable sustainable surrogates petroleum-based fuels. Bioethanol derived corn sugar cane United States Brazil, respectively, together account 84% total production. States, reached volume 15.7 billion gallons 2019 Department Energy, 2020aUS EnergyAlternative data centerGlobal statistics.2020https://afdc.energy.gov/data/10331Google Scholar), thus meeting mandatory 10% supplementation requirement gasoline (109th Congress, 2005109th CongressEnergy policy act 2005.2005Google Europe, lack cultivable land ban genetically modified limited 75% biofuel market European Union composed biodiesels rapeseed, palm oil, soybean, cooking oil. 2015, reduced 589.3 million tons 1) will continue play an important role energies (Biotechnology Innovation Organization (BIO), 2014Biotechnology (BIO)The Renewable Fuel Standard: A Decade’s worth reductions.2014https://www.bio.org/sites/default/files/legacy/bioorg/docs/RFS%2010%20Year%20GHG%20Reductions.pdfGoogle Recent battery technology substantially increased power density electrical storage devices, accelerating development electric vehicles. However, date, still predominantly gas coal (38% 23%, respectively) 2020bUS EnergyEnergy Information Administration (U.S.E.I.A)Monthly Energy Review.2020https://www.eia.gov/totalenergy/data/monthly/archive/00352003.pdfGoogle Furthermore, limitations driving range, capital cost, infrastructure, power-to-weight ratios preclude implementation long-haul vehicles aviation. To reach carbon-neutral -negative scheme, more diversified approach therefore requires both alike. Specifically, short-range light-weight configurations, whereas offers significant advantages conventional long-distance ground aircraft. mitigate demand, advancements focus (1) optimization current biofuel-production higher productivity efficiency lignocellulosic biomass (2) feedstocks ensure viability within existing ecological economic constraints (e.g., fixation photosynthetic means conversion biowaste into value-added products), (3) expansion designer molecules improve economy performance reducing emissions. Major devoted overcome barriers integrate social, factors long-term, cost-effective, reliable systems industry. Biofuel evolved several generations advancements. The predominant problem first-generation they cane), require fertilization, water, soil, directly compete Tight regulations pesticides limit their utilization transportation. order shortcomings, second-generation non-edible lignocellulose remnants plants, consist up 70% polymerized sugars constitute most abundant form Earth (Isikgor Becer, 2015Isikgor F.H. Becer C.R. Lignocellulosic biomass: platform bio-based chemicals polymers.Polym. Chem. 2015; 6: 4497-4559Crossref Google These attractive because net footprint (emitted – consumed carbon) neutral or even negative (Field et al., 2020Field J.L. Richard T.L. Smithwick E.A.H. Cai H. Laser M.S. LeBauer D.S. Long S.P. Paustian K. Qin Z. Sheehan J.J. al.Robust paths mitigation via advanced biofuels.Proc. Natl. Acad. Sci. USA. 2020; 117: 21968-21977Crossref PubMed Scopus (38) Scholar; Tilman 2006Tilman D. Hill J. Lehman C. Carbon-negative low-input high-diversity grassland biomass.Science. 2006; 314: 1598-1600Crossref (1327) agricultural forest residues white wood chips provides economical compared crops. using energetically financially costly extraction fermentable thermal, chemical, and/or biochemical pre-treatment. result, despite fact Independence Security Act (EISA) 2007 set annual blending target 16 cellulosic 2022 (110th 2007110th independence security 2007.2007Google 2017 had amounted less than 2% this benchmark 2020). Significant progress since made economically process, including strategies, degradation lignocellulose, simultaneous manufacturing higher-value products. benefits large-scale initially questioned competition reforestation; believed cultivation may result capture reforestation, leading debt must compensated negativity resulting biofuels. analysis switchgrass transitioning crop/pasture showed fact, comparable reforestation times restoration Additionally, ability sorghum grow marginal lands avenue minimizes necessary farmable support growing population (Jiang 2019Jiang Hao M. Fu Liu Yan X. Potential sweet China.J. Clean. Prod. 2019; 220: 225-234Crossref (29) Diallo 2019Diallo B. Li Tang Ameen A. Zhang W. Xie G.H. Biomass yield, composition theoretical different genotypes cultivated China.Ind. Crops 137: 221-230Crossref (13) maximize productive accumulating increasing capacity 2). Biological like non-photochemical quenching (NPQ) photorespiration suboptimal bioconversion photon fixed carbon. NPQ process dissipates excess (unproductive), state (productive) generally slow, mass loss field conditions. It overexpressing genes responsible relaxation Nicotiana tabacum accelerate switching ∼15% plant height, leaf area, (Kromdijk 2016Kromdijk Głowacka Leonelli L. Gabilly S.T. Iwai Niyogi K.K. Improving photosynthesis recovery photoprotection.Science. 2016; 354: 857-861Crossref (574) plants light much wasted. While counterintuitive, diminishing plant’s harvesting dense conditions drastic beneficial effect accumulation. truncation light-harvesting complex antenna components decreased lines 20% under (Kirst 2017Kirst Lemaux P.G. Melis Photosynthetic yields.Planta. 2017; 245: 1009-1020Crossref (55) Photorespiration another limits Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase’s (RuBisCO’s) react molecular oxygen place CO2 sequestration efficiency. Therefore, introducing photorespiratory bypass pathway (Shih 2014Shih P.M. Zarzycki Kerfeld C.A. Introduction synthetic CO2-fixing cyanobacterium.J. Biol. 2014; 289: 9493-9500Abstract Full Text PDF (64) South 2019South P.F. Cavanagh A.P. H.W. Ort D.R. Synthetic glycolate metabolism stimulate growth field.Science. 363: eaat9077Crossref (257) Eventually, many traits stacked individual technologies gene regulation developed (Belcher 2020Belcher Vuu K.M. Zhou Mansoori N. Agosto Ramos Thompson M.G. Scheller H.V. Loqué Shih Design orthogonal regulatory modulating expression plants.Nat. 16: 857-865Crossref (14) Metabolic synthesize products values incorporated meantime feasibility currently produced at far lower price biofuels, would viability. “Molecular farming,” couples high-value small proteins therapeutics antibodies, promising strategy value (Buyel, 2019Buyel J.F. Plant farming - integration exploitation side streams achieve biomanufacturing.Front. 9: 1893Crossref (43) Yang 2020Yang Baral N.R. Simmons B.A. Mortimer J.C. Scown C.D. Accumulation bioproducts planta economics 8639-8648Crossref (25) Accumulating after integrating background schemes processing pipeline drastically decrease costs, profits. additional implications medicine, cancer biologics viral antibodies levels without sterile (Capell 2020Capell T. Twyman R.M. Armario-Najera V. Ma J.K.-C. Schillberg S. Christou P. biotechnology against SARS-CoV-2.Trends 25: 635-643Abstract (80) Dent Matoba, 2020Dent Matoba Cancer plants.Curr. Opin. Biotechnol. 61: 82-88Crossref (5) Donini Marusic, 2019Donini Marusic Current state-of-the-art plant-based antibody systems.Biotechnol. Lett. 41: 335-346Crossref (35) Mortimer, 2019Mortimer biology drive revolution medicine.Exp. Med. (Maywood). 244: 323-331Crossref (20) one strategies although transgene biocontainment implemented prevent unwanted flow (Clark Maselko, 2020Clark Maselko Transgene farming.Front. 11: 210Crossref Because mismatch volumes needed versus each therapeutic needed, large number crops, producing same precursor products, agronomically challenging. relies cell-wall 3A) (Baral 2019Baral Sundstrom E.R. Das Gladden J.M. Eudes Singer S.W. Mukhopadhyay Approaches biological bioproducts.ACS Sustain. Chem.& Eng. 7: 9062-9079Crossref (46) Perez-Pimienta 2019Perez-Pimienta J.A. Papa G. Rodriguez Barcelos Liang Stavila Sanchez Pilot-scale hydrothermal pretreatment optimized saccharification enables bisabolene multiple feedstocks.Green 21: 3152-3164Crossref hurdle recalcitrance material inhibitory lignin (Dos Santos 2019Dos A.C. Ximenes E. Kim Y. Ladisch M.R. Lignin–enzyme Interactions hydrolysis biomass.Trends 37: 518-531Abstract (113) Cell-wall decreasing overall ratio C6/C5 sugars, content, acetylation polymers (Aznar 2018Aznar Chalvin Maimann Ebert Birdseye Gene stacking biomass.Biotechnol. Biofuels. 2018; 2Crossref 2015Eudes Sathitsuksanoh Baidoo E.E.K. George F. Singh Keasling J.D. Expression bacterial 3-dehydroshikimate dehydratase reduces content improves efficiency.Plant 13: 1241-1250Crossref 2018Yan Aznar Increased drought tolerance low xylan content.Biotechnol. 195Crossref (17) contributor recalcitrance, substrate specialized microbes convert aromatic usable (Fang 2020Fang Weisenberger M.C. Meier Utilization lignin-derived molecules: Epoxy oxidation products.ACS Appl. Bio Mater. 3: 881-890Crossref (6) Incha 2019Incha Blake-Hedges Pearson A.N. Schmidt Gin J.W. Petzold C.J. Deutschbauer A.M. Leveraging host bisdemethoxycurcumin Pseudomonas putida.Metab. Commun. 10: e00119PubMed introduction hosts various optimize value, limiting synergistic application make shifting paradigm what effective biofuel/bioproduct system achieves. Through multidisciplinary across sectors, we revolutionize biofuels/bioproducts ushering new era green technologies. second produce later fed microbes, third-generation combine single cell cyanobacteria algae 3B). Having entire fuel-production take organism makes direct invested non-fermentable parts stems, roots, leaves. solar reaching 3% microalgae 1% (Wijffels Barbosa, 2010Wijffels R.H. Barbosa M.J. An outlook microalgal biofuels.Science. 2010; 329: 796-799Crossref (1399) species wastewater marine environments simple nutritional requirements do agriculture. estimated oil 100,000 L/hectare/year, sunflower 1,000–6,000 L/hectare/year. Algal lead 9,000 L/hectare/year 600 (Alalwan 2019Alalwan H.A. Alminshid A.H. Aljaafari H.A.S. Promising evolution generations.Renew. Focus. 28: 127-139Crossref (97) Despite favorable comparisons, attempts cultivations struggled costs. Unlike agriculture, over millennia humans, scale microorganisms developmental stage. done either open raceway pond, closed photobioreactor. Open ponds operating costs risk contamination, strict organisms uncontained (Abdullah 2019Abdullah Syed Muhammad S.A.F. Shokravi Ismail Kassim K.A. Mahmood Aziz M.M.A. Fourth biofuel: review risks strategies.Renew. Rev. 107: 37-50Crossref (118) Closed systems, hand, tightly controlled contamination high: $2,743 per ton $1,227 (algae farm cost model) (Zhu 2018Zhu Jones S.B. Anderson D.B. Algae Farm Cost Model: Considerations Photobioreactors (Pacific Northwest National Laboratory, Energy).https://www.osti.gov/biblio/1485133Date: 2018Google lowered if following addressed: dissipation narrow spectrum, poor microbes. Light akin addressed similar strategy: chlorophyll (Melis 1999Melis Neidhardt Benemann J.R. Dunaliella salina (Chlorophyta) sizes exhibit productivities efficiencies normally pigmented cells.J. Phycol. 1999; 515-525Crossref (212) Scholar) modification size cyanobacterial photosystems solar-to-product 3-fold (Melis, 2009Melis Solar photosynthesis: Minimizing antennae 2009; 177: 272-280Crossref (473) issue visible range (400–700 nm), ∼50% incident inaccessible (Blankenship 2011Blankenship R.E. Tiede D.M. Barber Brudvig G.W. Fleming Ghirardi Gunner Junge Kramer al.Comparing photovoltaic recognizing improvement.Science. 2011; 332: 805-809Crossref (1064) terrestrial cyanobacteria, when grown far-red environments, express novel f (Chen 2010Chen Schliep Willows R.D. Z.-L. Neilan Scheer red-shifted chlorophyll.Science. 1318-1319Crossref (335) Heterologous pigment Synechococcus sp. PCC7002 successfully extended absorption 750 nm, thereby broadening spectrum (Tros 2020Tros Bersanini Shen Ho M.-Y. van Stokkum I.H.M. Bryant D.A. Croce R. Harvesting light: Functional Photosystem I complexes PCC 7002.Biochim. Biophys. Acta Bioenerg. 1861: 148206Crossref (15) nature RuBisCO, main fixing enzyme, suffers catalytic promiscuity O2. RuBisCO success trade-off between affinity carboxylation rate (Savir 2010Savir Noor Milo Tlusty Cross-species traces adaptation Rubisco optimality low-dimensional landscape.Proc. 3475-3480Crossref (180) alternative, engineer Calvin cycle regeneration RuBisCO’s substrate, ribulose-1,5-biphosphate (RuBP), resulted 69% (Liang 2018Liang Englund Lindberg Lindblad Engineered enhanced show ratio.Metab. 46: 51-59Crossref improved sink pulls away cycle. By 2,3-butanediol elongatus 7942, enzymes generating pyruvate 3-phosphoglycerate, was 1.8-fold (Oliver Atsumi, 2015Oliver J.W.K. Atsumi cyanobacteria.Metab. 29: 106-112Crossref (45) Unnatural introduced circumvent properties complicated regulation. Certain archaea reductive acetyl-CoA fix formate dehydrogenase CO dehydrogenase/acetyl-CoA synthase. ATP efficient, requiring 2 ATPs acetyl-CoA, 7 (Claassens 2016Claassens N.J. Sousa D.Z. Dos V.A.P.M. de Vos W.M. der Oost Harnessing autotrophy.Nat. Microbiol. 14: 692-706Crossref (101) anaerobic conditions, might transferability oxygenic photosynthesis. Nevertheless, vitro study demonstrated enoyl-CoA carboxylases/reductases better along three domains life circular where cofactors regenerated (Schwander 2016Schwander Schada von Borzyskowski Burgener Cortina N.S. Erb T.J. dioxide vitro.Science. 900-904Crossref (258) One key parameter dictates strain. store 80% dry weight lipids, making them strains accumulate carbohydrates fermented Further upregulate lipid triacylglycerol, De Bhowmick 2018De Koduru Sen towards enhancing biosynthesis application—A review.Renew. 50: 1239-1253Crossref (78) residual prot