Scientists are using the E. coli bacteria to process biomass into biofuels. Photo by the Lawrence Berkeley National Laboratory

Scientists seeking to formulate the next generation of biofuels often turn to genetically engineered microorganisms such as the Escherichia coli bacteria to process biomass into biofuels. The most recent example of this phenomenon was reported by a group of researchers from the United States Department of Energy's Joint Bioenergy Institute.

The J.B.E.I. worked with the E. coli bacterium - commonly known as the strain of bacteria that causes food poisoning - and came up with a strain that can digest switchgrass biomass and synthesize the sugars into cleaner alternatives to three different types of fuel: gasoline, diesel, and jet fuel.

While biomass from non-food crops and agricultural waste is widely believed to be a viable source for renewable replacements for petroleum-based fuels, there remains the fact that it is difficult to process and as such the cost of producing biofuels keeps it from being economically competitive.

Cellulose and hemicelluloses in plant biomass are sources of sugars that can be extracted and fermented into fuels, but they are difficult to extract because they are embedded in tough woody material called lignin.

Once extracted, these complex sugars must then undergo further processing to be converted to simple sugars that can then be used in fuels. These processes usually use a variety of microorganisms or enzymes.

The J.B.E.I. scientists engineered strains of the E. coli bacteria that can grow on switchgrass and express several enzymes that enable them to digest cellulose and hemicelluloses and use one or the other for growth.

They then took it a step further and engineered three metabolic pathways that enabled the bacteria to produce fuel substitute or precursor molecules suitable for gasoline, diesel, and jet engines.

While this is not the first demonstration of E. coli producing gasoline and diesel from sugars, according to the researchers it is the first demonstration of E. coli producing substitutes for all three forms of transportation fuel.

"This work shows that we can reduce one of the most expensive parts of the biofuel production process, the addition of enzymes to depolymerize cellulose and hemicellulose into fermentable sugars," says Jay Keasling, chief executive officer of J.B.E.I. and leader of this research.

According to Mr. Keasling, this will in turn reduce production costs by allowing for the extraction and fermentation of sugars to be done in one step.

The findings are described in a paper titled "Synthesis of three advanced biofuels from ionic liquid pretreated switchgrass using engineered Escherichia coli." The research was supported in part by the Department of Energy Office of Science and a University of California Discovery Grant.(Katrice R. Jalbuena)