Advanced biofuels -- liquid transportation fuels derived from the cellulosic biomass of perennial grasses and other non-food plants, as well as from agricultural waste -- are highly touted as potential replacements for gasoline, diesel and jet fuels. Equally touted is the synthesis of these fuels through the use of microbes. However, many of the best candidate compounds for advanced biofuels are toxic to microbes, which presents a "production versus survival" conundrum.
Researchers at the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI) have provided a solution to this problem by developing a library of microbial efflux pumps that were shown to significantly reduce the toxicity of seven representative biofuels in engineered strains of Escherichia coli.
"Working with all available microbial genome sequence data, we generated a library of largely uncharacterized genes and were able to devise a simple but highly effective strategy to identify efflux pumps that could alleviate biofuel toxicity in E. coli and, as a consequence, help improve biofuel production," says Aindrila Mukhopadhyay, a chemist with JBEI's Fuels Synthesis Division, who led this research.
Mukhopadhyay, who also holds an appointment with the Lawrence Berkeley National Laboratory (Berkeley Lab)'s Physical Biosciences Division, is the corresponding author on a paper published in the journal Molecular Systems Biology. Co-authoring the paper with Mukhopadhyay were Mary Dunlop, Zain Dossani, Heather Szmidt, Hou-Cheng Chu, Taek Soon Lee, Jay Keasling and Masood Hadi.
Research efforts are underway at JBEI and elsewhere to engineer microorganisms, such as E. coli, to produce advanced biofuels in a cost effective manner. These fuels, which encompass short-to-medium carbon-chain alcohols, such as butanol, isopentanol and geraniol, can replace gasoline on a gallon-for-gallon basis and be used in today's infrastructures and engines, unlike ethanol. Biofuels made from branched carbon-chain compounds, such as geranyl acetate and farnesyl hexanoate, would also be superior to today's biodiesel, which is made from esters of linear fatty acids. Cyclic alkenes, such as limonene and pinene, could serve as precursors to jet fuel. Although biosynthetic pathways to the production of these carbon compounds in microbes have been identified, product toxicity to microbes is a common problem in strain engineering for biofuels and other biotechnology applications.