Plant cell walls contain a renewable, nearly limitless supply of sugar that can be used in the production of chemicals and biofuels. However, retrieving these sugars isn&rsquo;t all that easy.
Imidazolium ionic liquid (IIL) solvents are one of the best sources for extracting sugars from plants. But the sugars from IIL-treated biomass are inevitably contaminated with residual IILs that inhibit growth in bacteria and yeast, blocking biochemical production by these organisms.
Lawrence Livermore National Laboratory scientists and collaborators at the&nbsp;<a href="http://www.jbei.org/" target="_blank">Joint BioEnergy Institute</a>&nbsp;have identified a molecular mechanism in bacteria that can be manipulated to promote IIL tolerance, and therefore overcome a key gap in biofuel and biochemical production processes. The research appears in the&nbsp;<a href="https://jb.asm.org/" target="_blank">Journal of Bacteriology</a>.
&ldquo;Ionic liquid toxicity is a critical roadblock in many industrial biosynthetic pathways,&rdquo; said LLNL biologist Michael Thelen, lead author of the paper. &ldquo;We were able to find microbes that are resistant to the cytotoxic effects."
The team used four&nbsp;bacillus&nbsp;strains that were isolated from compost (and a mutant&nbsp;E. coli&nbsp;bacterium) and found that two of the strains and the&nbsp;E. colimutant can withstand high levels of two widely used IILs.
Douglas Higgins, a postdoc working with Thelen at the time, dived into how exactly the bacteria do this. In each of the bacteria, he identified a membrane transporter, or pump, that is responsible for exporting the toxic IIL. He also found two cases in which the pump gene contained alterations in the RNA sequence of a regulatory guanidine riboswitch. Guanidine is a toxic byproduct of normal biological processes; however, cells need to get rid of it before it accumulates.
The normal, unmodified riboswitch interacts with guanidine and undergoes a conformational change, causing the pump to switch on and make the bacterial cells resistant to IILs.
&ldquo;Our results demonstrate the critical roles that transporter genes and their genetic controls play in IIL tolerance in their native bacterial hosts,&rdquo; Thelen said. &ldquo;This is just another step in engineering IIL tolerance into industrial strains and overcoming this key gap in biofuel production.&rdquo;
The results could help identify genetic engineering strategies that improve conversion of cellulosic sugars into biofuels and biochemicals in processes where a low concentration of ionic liquids surpass bacterial tolerance.
Scientists from&nbsp;<a href="https://www.sandia.gov/" target="_blank">Sandia National Laboratories</a>&nbsp;and&nbsp;<a href="https://www.lbl.gov/" target="_blank">Lawrence Berkeley National Laboratory</a>&nbsp;also contributed to this research.
The work is funded by the Department of Energy's&nbsp;<a href="https://www.energy.gov/science/office-science" target="_blank">Office of Science</a>.
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Switchgrass is used as a biomass crop for advanced biofuel production

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LLNL scientists and collaborators at the Joint BioEnergy Institute have identified a molecular mechanism in bacteria that can be manipulated to promote IIL tolerance, and therefore overcome a key gap in biofuel and biochemical production processes. 

LLNL: Turning the switch on biofuels

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