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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Xylose Assimilation for the Efficient Production of Biofuels and Chemicals by Engineered Saccharomyces cerevisiae

Microbial conversion of plant biomass into fuels and chemicals offers a practical solution to global concerns over limited natural resources, environmental pollution, and climate change. Pursuant to these goals, researchers have put tremendous efforts and resources towards engineering the yeast Saccharomyces cerevisiae to efficiently convert xylose, the second most abundant sugar in lignocellulosic biomass, into various fuels and chemicals. Here, we summarize recent advances in metabolic engineering of yeast to address bottlenecks on xylose assimilation, and to enable simultaneous co-utilization of xylose and other carbon sources in lignocellulosic hydrolysates. We also highlight distinct characteristics of xylose metabolism that can be harnessed to produce advanced biofuels and chemicals. Although many challenges remain, recent research investments have facilitated efficient fermentation of xylose and simultaneous co-consumption of xylose and glucose. In particular, understanding of xylose-induced metabolic rewiring in engineered yeast has encouraged use of xylose as a carbon source for producing various non-ethanol bioproducts. Furthermore, to boost the lignocellulosic biomass-based bioeconomy, much attention is expected to promote xylose-utilizing efficiency via reprogramming cellular regulatory networks, to attain robust co-fermentation of xylose and other cellulosic carbon sources under industrial conditions, and to exploit the advantageous traits of yeast xylose metabolism for producing diverse fuels and chemicals.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Production of Polyhydroxybutyrate from Ralstonia eutropha H-16 Using Makgeolli Lees Enzymatic Hydrolysate

The objective of this study was to investigate the potential use of waste Makgeolli lees (ML), a by-product of Makgeolli production, as a feedstock for biorefinery production of polyhydroxybutyrate (PHB). ML enzymatic hydrolysate (MLEH) was prepared from ML subjected to liquefaction with amylase and subsequent saccharification with glucoamylase. Since MLEH contains glucose (81 g/L) and protein (39 g/L) among other elements, it was used as the carbon source for PHB production by Ralstonia eutropha H-16. After flask incubation with MLEH, the obtained biomass and PHB content were 10.03 g/L and 34%, respectively, which were higher than the contents obtained when using glucose as the sole carbon source. However, batch fermentation resulted in low PHB accumulation despite suitable cell growth being observed, and these results were thought to be due to the unbalanced C/N ratio. To control the C/N ratio to 20:1, sterile glucose solution was added twice in the fed-batch fermentation with MLEH, and we could obtained dry cell weight and PHB of 36.9 g/L and 24.1 g/L, respectively. Therefore, this study demonstrated the potential use of waste ML as a feedstock for industrial PHB production, which has the important advantage of reduced production cost.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Conversion of Corn Stover Hydrolysates to Acids: Comparison Between Clostridium carboxidivorans P7 and Microbial Communities Developed from Lake Sediment and an Anaerobic Digester

Anaerobic fermentation is an environmentally sustainable technology for converting a variety of feedstocks to biofuels and bioproducts. Considering the complex nature of lignocellulosic hydrolysates, we aimed to investigate product formation from corn stover hydrolysates by using microbial communities under anaerobic conditions. A community developed from lake sediment was able to produce lactic acid from only glucose in the raw or overlimed hydrolysates. Another community from an anaerobic digester, however, was capable of using all hexose and pentose sugars in the raw and undetoxified hydrolysates and released lactic acid at 26.76 g/L. A pure acetogen, Clostridium carboxidivorans P7, was able to grow on the raw and overlimed hydrolysates, too. But the consumption of sugars was minimal and the total released acid concentrations were less than 2 g/L. Next generation sequencing of the enriched community derived from the anaerobic digester revealed the presence of Lactobacillus strains. The predominant species were Lactobacillus parafarraginis (72.6%) and L. buchneri (13.4%). Product titer from using this enriched community can be further enhanced by cultivating at fed-batch or continuous fermentation modes. Results from this study widened the door for producing valuable products from lignocellulosic feedstocks through using mixed cultures.

09 BIOMASS FUELS↗
DOE OSTI2017

Disposition and bioavailability of inulin and free sugar in untreated and dilute acid pretreated Agave tequilana leaves

Industrially, the Agave tequilana plant is most commonly associated with beverage production, which requires it to be grown for 8–10 year before harvesting. However, its robust growth characteristics and low water usage requirements suggest that it could also be utilized as a substrate for alternative fermentation processes that do not require such long crop turnover times. Therefore, a study was undertaken to characterize the feasibility of utilizing the leaves from two year-old plants as a microbial fermentation biomass substrate. Quantitative saccharification revealed the carbohydrate concentration of two year-old A. tequilana leaves to be 633 mg g -1 dry weight biomass. HPLC analysis identified the primary carbohydrates as glucans, with minor contributions from xylans, galactans, arabinanas, and mannans. Fructose was observed predominantly as inulin. The direct use of unpretreated A. tequilana leaf biomass as a sole carbon source could support yeast growth, however, dilute acid pretreatment removed sufficient levels of carbohydrates to prevent the growth of wild type or inulinase-expressing yeast strains. Up to 133.5 g kg -1 of soluble carbohydrates and 69.6 g kg -1 of soluble inulin were extracted in the pretreatment soakate and 4.0 g kg -1 1 of soluble carbohydrates and 1.3 g kg -1 of soluble inulin remained in the biomass post processing. Ultimately, inulinase gene expression did not significantly improve yeast growth rates, but permitted up to 6.3 g kg -1 of the available soluble inulin from the dilute acid pretreatment soakate to be metabolized towards cellular growth.

09 BIOMASS FUELS↗
DOE OSTI2019

Membrane assisted continuous production of solvents with integrated solvent removal using liquid-liquid extraction

The aim was to demonstrate an industrially relevant pilot scale integrated process to produce butanol and other solvents from lignocellulosic sugars produced with AVAP® biomass fractionation technology from southern pine wood. The concentrated sugars were concurrently fermented using genetically engineered Clostridium acetobutylicum to n-butanol, acetone, isopropanol and ethanol in continuous membrane assisted cell recycle fermentation with steady-state solvent productivity exceeding 10 g/L/h. The solvents from the cell free permeate were recovered with extractant of butyl butyrate in a continuous liquid-liquid extraction column and aqueous product (raffinate) along with unused sugars, nutrients, and metabolic intermediates were recycled back to the fermentors. The total solvent yield approached 0.30 g/g sugars.

09 BIOMASS FUELS↗
DOE OSTI2025

Cost impact of hexose-to-pentose sugar ratios for biomanufacturing

Central to the long-term vision for biomanufacturing is the ability to deconstruct plant cell walls to sugars that microbes can convert to products. Aside from glucose, the most abundant sugar in biomass is xylose, a pentose sugar. Industrially relevant microbes have been engineered to co-ferment xylose and glucose. Most nth plant technoeconomic analyses (TEAs) assume similar consumption rates and product yields for both sugars, but in reality, xylose is consumed more slowly. Feedstocks can be selected, or engineered, to alter the glucan-to-xylan ratio (GXR) but no TEAs have quantified the impact of this strategy systematically. This study explores the cost impacts of varying the glucan-to-xylan ratio (GXR) from 1.9 to 6.7 for co-fermenting glucose and xylose to ethanol and bisabolene. The minimum selling prices (MSPs) for both products decrease as the GXR increases, with the largest reductions at shorter residence times. For instance, with an increase in GXR from 1.9 to 6.7, ethanol’s MSP drops by 16 %, 5 %, and 3 % at 24, 72, and 144 h, respectively, while bisabolene’s MSP declines by 23 %, 20 %, and 15 % at 24, 72, and 120 h. Particularly for early-stage commercialization, the results suggest that altering or selecting for feedstocks with higher GXR can minimize capital costs by reducing optimal residence times. Capital-constrained biorefineries operating with shorter residence times can justify paying up to 1.5X to 2X the price for feedstocks with a higher GXR, based on the expected improvements in their product yield and overall process economics.

Delayed xylose utilization↗
DOE OSTI2018

Butyric acid: Applications and recent advances in its bioproduction

Butyric acid is an important C4 organic acid with broad applications. It is currently produced by chemosynthesis from petroleum-based feedstocks. However, the fermentative production of butyric acid from renewable feedstocks has received growing attention because of consumer demand for green products and natural ingredients in foods, pharmaceuticals, animal feed supplements, and cosmetics. In this review, strategies for improving microbial butyric acid production, including strain engineering and novel fermentation process development are discussed and compared regarding product yield, titer, purity and productivity. Future perspectives on strain and process improvements for butyric acid production are also discussed.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Microbial production of fuels, commodity chemicals, and materials from sustainable sources of carbon and energy

Anthropogenic carbon emissions are driving rapid changes to the earth's climate, disrupting whole ecosystems and endangering the stability of human society. Innovations in engineered microbial fermentation enable the fossil resource-free production of fuels, commodity chemicals, and materials, thereby reducing the carbon emissions associated with these products. Microorganisms have been engineered to catabolize sustainable sources of carbon and energy (i.e., plant biomass, plastic waste, and one-carbon feedstocks) and biosynthesize carbon-neutral or carbon-negative products. These engineering efforts exploit and optimize natural biological pathways or generate unnatural pathways which can biosynthesize chemicals that have not yet been accessed using synthetic chemistry. Further, recent advances in microbial fermentation seek not only to maximize the titer, rate, and yield of desired products, but also to tailor microbial catabolism to utilize inexpensive feedstocks. Ultimately, these advances aim to lower the cost of bioproduction so that microorganism-derived chemicals can be economically competitive with fossil-derived chemicals.

09 BIOMASS FUELS↗
DOE OSTI2017

Cellulosic ethanol: status and innovation

Although the purchase price of cellulosic feedstocks is competitive with petroleum on an energy basis, the cost of lignocellulose conversion to ethanol using today’s technology is high. Cost reductions can be pursued via either in-paradigm or new-paradigm innovation. As an example of new-paradigm innovation, consolidated bioprocessing using thermophilic bacteria combined with milling during fermentation (cotreatment) is analyzed. Acknowledging the nascent state of this approach, our analysis indicates potential for radically improved cost competitiveness and feasibility at smaller scale compared to current technology, arising from (a) R&D-driven advances (consolidated bioprocessing with cotreatment in lieu of thermochemical pretreatment and added fungal cellulase), and (b) configurational changes (fuel pellet coproduction instead of electricity, gas boiler(s) in lieu of a solid fuel boiler).

Lynd, Lee R.↗
DOE OSTI2020

Modified alkaline peroxide pretreatment: An efficient path forward for bioethanol production from bamboo

To overcome the typical delignification saturation point of alkaline peroxide pretreatment and further facilitate lignin removal, a novel modified alkaline hydrogen peroxide pretreatment (MAHP) was proposed by introducing ethanol into the reaction system. The dosages of H 2 O 2 , ethanol, and pretreatment temperature were optimized, and the results revealed that a maximum lignin removal as high as 79.25% could be achieved at only 100 °C, 3 wt% H 2 O 2 concentration and 1 wt% ethanol concentration. Meanwhile, 76.5% of glucan and 56.0% of xylan were preserved at this pretreatment condition. By overcoming the delignification saturation point, enzymatic hydrolysis efficiency was remarkably enhanced, achieving 96.76% and 97.38% of glucan and xylan conversion, respectively, which are 7.4 and 11.4 times as compared to that of the untreated bamboo. Furthermore, the simultaneous saccharification and fermentation (SSF) result indicated an identical ethanol yield of ~75% when elevating the SSF solid loading from 5% to 30%. Based on the sequential SSF and xylose fermentation results, about 5.6 tons of bamboo would be consumed to produce 1 ton of ethanol. Finally, the energy balance revealed that a positive balance of 1255.4 KJ could be generated via processing 1 kg bamboo. Here, the results demonstrate that the MAHP is a promising high-efficiency pretreatment technology for bamboo due to the mild pretreatment severity and robust ethanol yield.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Degradation of aromatic compounds and lignin by marine protist Thraustochytrium striatum

This paper aimed at studying a novel high biomass strain (HBS) of marine protist, Thraustochytrium striatum, for lignin valorization to lipids and carotenoids. In the screening of 15 aromatic compounds, T. striatum HBS can utilize most compounds while achieving the best growth on 3,4-dihydroxybenzoic acid (3,4-DHBA) and 4-hydroxybenzoic acid (4-HBA). The maximum cell mass concentration reached 2-3 g/L under 5 g/L of 3,4-DHBA or 2 g/L of 4-HBA, which was comparable to that under equivalent concentration of glucose. The long-chain fatty acids content was 13 % and 7 % with 3,4-DHBA and 4-HBA, respectively. The adoption of fed-batch fermentation mode improved the degradation of carbon source and prevented the inhibitory effect caused by overloading of aromatic compounds. Further, both final cellular fatty acids and carotenoids contents were doubled in the fermentation of 3,4-DHBA. T. striatum HBS exhibited limited lignin depolymerization (~24 %) ability on technical lignins.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Stimulation of anaerobic organic matter decomposition by subsurface organic N addition in tundra soils

We present that increasing nitrogen (N) availability in Arctic soils could stimulate the growth of both plants and microorganisms by relieving the constraints of nutrient limitation. It was hypothesized that organic N addition to anoxic tundra soil would increase CH 4 production by stimulating the fermentation of labile substrates, which is considered the rate-limiting step in anaerobic C mineralization. We tested this hypothesis through both field and lab-based experiments. In the field experiment, we injected a solution of 13 C- and 15 N-labeled glutamate 35 cm belowground at a site near Nome on the Seward Peninsula, Alaska, and observed the resulting changes in porewater geochemistry and dissolved greenhouse gas concentrations. The concentration of free glutamate declined rapidly within hours of injection, and the 15 N label was recovered almost exclusively as dissolved organic N within 62 h. These results indicate rapid microbial assimilation of the added N and transformation into novel organic compounds. We observed increasing concentrations of dissolved CH 4 and Fe(II), indicating rapid stimulation of methanogenesis and Fe(III) reduction. Low molecular weight organic acids such as acetate and propionate accumulated despite increasing consumption through anaerobic C mineralization. A laboratory soil column flow experiment using active layer soil collected from the same site further supported these findings. Glutamate recovery was low compared to a conservative bromide tracer, but concentrations of NO 3 - and NH 4 + remained low, consistent with microbial uptake of the added N. Similar to the field experiment, we observed both increasing Fe(II) and organic acid concentrations. Lastly, together, these results support our hypothesis of increased fermentation in response to organic N addition and suggest that increasing N availability could accelerate CH 4 production in tundra soils.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Experimental and life cycle assessment analysis of gas emission from mechanically–biologically pretreated waste in a landfill with energy recovery

Highlights: • Bio-methane landfill emissions from different period (0, 4, 8, 16 weeks) MTB waste have been evaluated. • Electrical energy recoverable from landfill gas ranges from 11 to about 90 kW h/tonne. • Correlation between oxygen uptake, energy recovery and anaerobic gas production shows R{sup 2} ranging from 0.78 to 0.98. • LCA demonstrate that global impact related to gaseous emissions achieve minimum for 4 week of MBT. - Abstract: The global gaseous emissions produced by landfilling the Mechanically Sorted Organic Fraction (MSOF) with different weeks of Mechanical Biological Treatment (MBT) was evaluated for an existing waste management system. One MBT facility and a landfill with internal combustion engines fuelled by the landfill gas for electrical energy production operate in the waste management system considered. An experimental apparatus was used to simulate 0, 4, 8 and 16 weeks of aerobic stabilization and the consequent biogas potential (Nl/kg) of a large sample of MSOF withdrawn from the full-scale MBT. Stabilization achieved by the waste was evaluated by dynamic oxygen uptake and fermentation tests. Good correlation coefficients (R{sup 2}), ranging from 0.7668 to 0.9772, were found between oxygen uptake, fermentation and anaerobic test values. On the basis of the results of several anaerobic tests, the methane production rate k (year{sup −1}) was evaluated. k ranged from 0.436 to 0.308 year{sup −1} and the bio-methane potential from 37 to 12 N m{sup 3}/tonne, respectively, for the MSOF with 0 and 16 weeks of treatment. Energy recovery from landfill gas ranged from about 11 to 90 kW h per tonne of disposed MSOF depending on the different scenario investigated. Life cycle analysis showed that the scenario with 0 weeks of pre-treatment has the highest weighted global impact even if opposite results were obtained with respect to the single impact criteria. MSOF pre-treatment periods longer than 4 weeks showed rather negligible variation in the global impact of system emissions.

09 BIOMASS FUELS↗
DOE OSTI2015

Co-digestion of wheat and rye bread suspensions with source-sorted municipal biowaste

Graphical abstract: Volatile fatty acid spectra of acidified WBS, RBS or FBS differ, but methanogenesis is similar. Display Omitted - Highlights: • Biogas improvement by co-digestion of wheat and rye bread. • Increased population density at high organic loading rates. • Less Pelotomaculum but increased numbers of Syntrophobacter and Smithella found in rye bread reactor. • Replacement of Methanosarcinales by acetate-oxidizers in rye bread co-digestion. • Increasing proportion of Methanomicrobiales in biowaste + rye bread reactor. - Abstract: Acidification of wheat bread (WBS), rye bread (RBS) and fresh biowaste suspensions (FBS), leading to lactate+acetate, lactate+acetate+n-buyrate, and acetate+propionate+n-butyrate, respectively, and biogas production as well as population dynamics were investigated. Co-fermentation of FBS (14 kg m{sup −3} d{sup −1} organic loading rate (OLR)) with WBS or RBS was stable up to an OLR of 22 kg m{sup −3} d{sup −1} and resulted in up to 3 times as much biogas. During co-fermentation at more than 20 kg m{sup −3} d{sup −1} OLR the total population increased more than 2-fold, but the originally low share of propionate-oxidizing bacteria significantly decreased. The proportion of methanogens also decreased. Whereas the proportion of Methanosarcinales to Methanomicrobiales in biowaste and biowaste+WBS remained constant, Methanosarcinales and in particular Methanosaeta spec. in the biowaste+RBS assay almost completely disappeared. Methanomicrobiales increased instead, indicating propionate oxidation via acetate cleavage to CO{sub 2} and hydrogen.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Comparison of the acidogenic and methanogenic potential of agroindustrial residues

Highlights: • Mixed acidogenic fermentation shows lower yields but higher product value than methanogenesis. • VFA concentrations reported are among the highest in literature for batch acidogenic fermentation. • Trub is an attractive residue for valorisation due to the potential for caproic acid production. • Brewery residues have a significant economic potential. - Abstract: The methanogenic and acidogenic potentials of six different agroindustrial residues, i.e. of fruit pulps and brewery residues, were determined. For all substrates, the methanogenic conversion yield was systematically higher than the acidogenic one in Chemical Oxygen Demand (COD) terms, ranging from 0.46 to 0.87 g{sub COD{sub CH4}}/{sub gCOD{sub substrate{sub fed}}} and from 0.24 to 0.56 g{sub COD{sub tVFA}}/g{sub COD{sub substrate{sub fed}}}, respectively. During methanogenic conversion, brewery trub exhibited the highest methane potential (304 ml{sub CH4}/g{sub COD{sub substrate}}). Trub also exhibited the highest total volatile fatty acids (tVFA) concentrations in the mixed liquor (ML) during acidogenic conversion (29.7 g{sub COD{sub tVFA}}/kg{sub ML}). Acetic, butyric and caproic acids were the main carboxylates produced by the different substrates. Despite the lower conversion yields, the economic value of the acidogenic product (carboxylate streams) is higher than that of methanogenic conversion (methane) due to the higher value of carboxylates and their potential use in finer applications (e.g. bio-based products) compared to energy production form methane.

09 BIOMASS FUELS↗
DOE OSTI2021

Process Intensification for the Biological Production of the Fuel Precursor Butyric Acid from Biomass

The production of fuels from lignocellulosic biomass is key to reduce our reliance on petroleum and to promote a sustainable bioeconomy. Butyric acid (BA) is a promising chemical precursor for the production of renewable diesel and jet fuels. BA can be biologically produced from lignocellulosic sugars. However, challenges associated with product selectivity and recovery must be overcome to achieve industrially relevant metrics. Here, we evaluate various fermentation configurations and demonstrate near-homo-butyrate production by using the biocatalyst Clostridium tyrobutyricum. We also develop an advanced in situ product recovery process based on hybrid extraction-distillation (HED-ISPR) and conduct techno-economic analyses and life cycle assessments. We demonstrate that the HED-ISPR process lowers the overall capital and operating expenses and environmental impact compared to other traditional fermentation processes. Overall, BA minimum product selling price from biomass is 55% of the current BA selling price from petroleum, a significant decrease toward viable renewable fuel production.

09 BIOMASS FUELS↗
DOE OSTI2018

Engineering a spermidine biosynthetic pathway in Clostridium thermocellum results in increased resistance to furans and increased ethanol production

Polyamines are low molecular weight aliphatic nitrogen compounds found ubiquitously in microorganisms, plants, and animals. Spermidine is a common polyamine that plays a role in stabilizing chromatin, DNA replication, transcription, translation, as well as the regulation of cell growth and apoptosis in eukaryotes. Amines are also associated with defense to a number of environmental stresses including elevated temperature and have been shown to be involved in tolerance to fermentation inhibitors such as furan derivatives and acetic acid in Saccharomyces cerevisiae. While the tolerance and detoxifying mechanisms have been intensively studied, metabolic engineering efforts to construct tolerant and resistant strains have been few. Here, in this work, we show that exogenously added spermidine confers enhanced tolerance to furans and acetic acid in the Gram-positive bacterium, Clostridium thermocellum . Deletion of the endogenous spermidine synthase resulted in a severe growth defect and hypersensitivity to both furans and acetic acid. Exogenously added spermidine rescued all three phenotypes. Overexpression of the endogenous spermidine synthase resulted in increased tolerance to these compounds without added spermidine. Increased tolerance to these fermentation inhibitors will facilitate the use of C. thermocellum , one of the most cellulolytic of all known bacterial species, for the production of fuels from plant biomass substrates.

Biofuels↗
DOE OSTI2025

Feedstock-efficient conversion through hydrogen and formate-driven metabolism in Escherichia coli

Product yields for biomanufacturing processes are often constrained by the tight coupling of cellular energy generation and carbon metabolism in sugar-based fermentation systems. To overcome this limitation, we engineered Escherichia coli to utilize hydrogen gas (H 2 ) and formate (HCOO - ) as alternative sources of energy and reducing equivalents, thereby decoupling energy generation from carbon metabolism. This approach enabled precise suppression of decarboxylative oxidation during acetate growth, with 86.6 ± 1.6 % of electrons from hydrogen gas (via soluble hydrogenase from Cupriavidus necator H16) and 98.4 ± 3.6 % of electrons from formate (via formate dehydrogenase from Pseudomonas sp. 101) offsetting acetate oxidation. Hydrogen gas supplementation led to a titratable and stoichiometric reduction in CO 2 evolution in acetate-fed cultures. Metabolomic analysis suggests that this metabolic decoupling redirects carbon flux through the glyoxylate shunt, partially bypassing two decarboxylative steps in the TCA cycle. Here, we demonstrated the utility of this strategy by applying it to mevalonate biosynthesis, where formate supplementation during glucose fermentation increased titers by 57.6 % in our best-performing strain. Flux balance analysis further estimated that 99.0 ± 2.8 % of electrons from formate were used to enhance mevalonate production. These findings highlight a broadly applicable strategy for enhancing biomanufacturing efficiency by leveraging external reducing power to optimize feedstock and energy use.

Biomanufacturing↗