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  • Turning Biomass into Biofuel

    2010 - 02.17

    A microbe has been developed by the US Department of Energy’s Joint BioEnergy Institute or JBEI if you prefer the abbreviation. This microbe is reported to produce an advanced form of biofuel that comes directly from biomass. The JBEI researchers discovered it by deploying the tools of synthetic biology to engineer a strain of Escherichia coli (or more commonly known as E. coli) bacteria. This is able to produce biodiesel fuel and other important chemicals derived from fatty acids.

    “The fact that our microbes can produce a diesel fuel directly from biomass with no additional chemical modifications is exciting and important,” says Jay Keasling, the Chief Executive Officer for JBEI, and a leading scientific authority on synthetic biology. “Given that the costs of recovering biodiesel are nowhere near the costs required to distill ethanol, we believe our results can significantly contribute to the ultimate goal of producing scalable and cost effective advanced biofuels and renewable chemicals.”

    The results of this research were published in the 28th January 2010 edition of the journal Nature. The paper is titled ‘Microbial Production of Fatty Acid-Derived Fuels and Chemicals from Plant Biomass.’

    There is increasing global demand for renewable and sustainably produced fuel. This and many other studies have shown that liquid fuels derived from plant biomass are one of the best alternatives. The only problem with this method is that for now it is produced on a small scale and will continue to be until a cost-effective means of commercial production can be found.

    To this end research has centred on energy rich molecules in living cells that have been dubbed nature’s petroleum or fatty acids to you and me. For over a century fuels and chemicals have been produced from the fatty acids in plant and animal oils. Now these oils are the key ingredient for biodiesel fuels as well as a wide variety of other chemical products.

    “The increased demand and limited supply of these oils has resulted in competition with food, higher prices, questionable land-use practices and environmental concerns associated with their production,” Keasling says. “A more scalable, controllable, and economic alternative route to these fuels and chemicals would be through the microbial conversion of renewable feed stocks, such as biomass-derived carbohydrates.”

    E. coli has a natural ability to synthesize fatty acids and has an exceptional amenability to genetic manipulation, which makes it an ideal target for biofuels research. It was the combination of E. coli with new biochemical reactions realised through synthetic biology that allowed the JBEI researchers to produce biodiesel, alcohol and waxes directly from sugar.

    “Biosynthesis of microbial fatty acids produces fatty acids bound to a carrier protein, the accumulation of which inhibits the making of additional fatty acids,” Steen says. “Normally E. coli don’t waste energy making excess fat, but by cleaving fatty acids from their carrier proteins, we’re able to unlock the natural regulation and make an abundance of fatty acids that can be converted into a number of valuable products. Further, we engineered our E. coli to no longer eat fatty acids or use them for energy.”

    After successfully diverting fatty acid metabolism toward the production of fuels and other chemicals from glucose, the JBEI researchers engineered their new strain of E. coli to produce hemicellulases — enzymes that are able to ferment hemicellulose, the complex sugars that are a major constituent of cellulosic biomass and a prime repository for the energy locked within plant cell walls.

    “Engineering E. coli to produce hemicellulases enables the microbes to produce fuels directly from the biomass of plants that are not used as food for humans or feed for animals,” Steen says. “Currently, biochemical processing of cellulosic biomass requires costly enzymes for sugar liberation. By giving the E. coli the capacity to ferment both cellulose and hemicellulose without the addition of expensive enzymes, we can improve the economics of cellulosic biofuels.”

    Currently the JBEI researchers are working on getting the most out of the efficiency and the speed by which their engineered strain of E. coli can be directly converted from biomass into biodiesel. In addition they are looking into ways of maximising the total amount of biodiesel that is produced from a single fermentation.

    “Productivity, titer and efficient conversion of feedstock into fuelare the three most important factors for engineering microbes that can produce biofuels on an industrial scale,” Steen says. “There is still much more research to do before this process becomes commercially feasible.”

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