In the search for technology by which economically competitive biofuels can be produced from cellulosic biomass, the combination of sugar-fermenting microbes and ionic liquid solvents looks to be a winner save for one major problem: the ionic liquids used to make cellulosic biomass more digestible for microbes can also be toxic to them. A solution to this conundrum, however, may be in the offing.
Researchers with the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI), a multi-institutional partnership led by Berkeley Lab, have identified a tropical rainforest microbe that can endure relatively high concentrations of an ionic liquid used to dissolve cellulosic biomass. The researchers have also determined how the microbe is able to do this, a discovery that holds broad implications beyond the production of advanced biofuels.
"Our findings represent an important first step in understanding the mechanisms of ionic liquid resistance in bacteria and provide a basis for engineering ionic liquid tolerance into strains of fuel-producing microbes for a more efficient biofuel production process," says Blake Simmons, a chemical engineer who heads JBEI's Deconstruction Division and one of the senior investigators for this research.
The burning of fossil fuels releases nearly 9 billion metric tons of excess carbon into the atmosphere each year. Meanwhile the global demand for gasoline and other petroleum-based fuels continues to rise. Clean, green and renewable fuels that won't add excess carbon to the atmosphere are sorely needed. Among the best candidates are advanced biofuels synthesized from the cellulosic biomass in non-food plants. Such fuels could displace petroleum-based fuels on a gallon-for-gallon basis and be incorporated into today's vehicles and infrastructures with no impact on performance.
To this end, researchers at JBEI have already engineered a strain of E. coli bacteria to digest the cellulosic biomass of switchgrass, a perennial grass that thrives on land not suitable for food crops, and convert its sugars into biofuel replacements for gasoline, diesel and jet fuels. A key to this success was the pretreatment of the switchgrass with an ionic liquid to dissolve it.
"Unlike the starch sugars in grains, the complex polysaccharides in cellulosic biomass are semicrystalline and deeply embedded within a tough woody material called lignin," Simmons says. "Lignin can be removed and cellulose crystallinity can be reduced if the biomass is pretreated with ionic liquids, environmentally benign organic salts often used as green chemistry substitutes for volatile organic solvents."
Current strategies for processing cellulosic biomass into biofuels involve multiple production steps in which the bulk of ionic liquids used to pretreat biomass can be washed out before the microbes are added. However, to cut production costs, a "one pot" strategy in which processing steps take place in a single vat would be highly desirable. This strategy requires microbes that can tolerate and grow in ionic liquids used to pretreat cellulosic biomass.
In search of such microbes, a team of JBEI researchers led by microbiologist and PNAS paper co-author Kristen DeAngelis ventured into the El Yunque National Forest in Puerto Rico, a tropical rain forest where microbial communities have demonstrated exceptionally high rates of biomass decomposition, and a tolerance to high osmotic pressures of the sort generated by exposure to ionic liquids. They returned with a prime candidate in the SCF1 strain of Enterobacter lignolyticus.
"We first determined that the SCF1 strain of Enterobacter lignolyticus grows in the presence of the ionic liquid [C2mim]Cl at concentrations comparable to the concentrations that remain in the cellulose after pretreatment and recovery," Thelen says. "Next, through a combination of phenotypic growth assays, phospholipid fatty acid analysis, and RNA sequencing technologies, we investigated the mechanisms by which SCF1 tolerates this ionic liquid."
Working in collaboration with researchers at DOE's Joint Genome Institute, another multi-institutional partnership led by Berkeley Lab, Thelen and Simmons and their JBEI colleagues developed a preliminary model of ionic liquid tolerance for SCF1.
"Our model suggests that SCF1 bacteria resist the toxic effect of the [C2mim]Cl ionic liquid by altering the permeability of their cell membrane and pumping the toxic chemical out of the cell before damage occurs," Thelen says. "These detoxifying mechanisms are known to be involved in bacterial responses to stress, but not in a coordinated manner as we have shown for the response of SCF1 to ionic liquid."
Thelen says the information gained from this study will be used at JBEI to help engineer new fuel-producing microbes that can tolerate ionic liquid pretreatments. Beyond biofuels, the techniques developed in this study should also be applicable to the screening of microbial responses to other chemical compounds, such as antibiotics.
This work was supported by the DOE Office of Science.Blake Simmons, in addition to his JBEI appointment, is also a scientist with the Sandia National Laboratory. Michael Thelen, in addition to his JBEI appointment, is also a scientist with the Lawrence Livermore National Laboratory.
Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit www.lbl.gov.
DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the Unites States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov.
Lynn Yarris | EurekAlert!
Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH
Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences