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Altered microbe makes biofuel

Bacterium could work directly on grass or crop waste.

Switch grass could be made into diesel cleanly and quickly. Credit: PVSTOCK.COM/ALAMY

In a bid to overcome the drawbacks of existing biofuels, researchers have engineered a bacterium that can convert a form of raw plant biomass directly into clean, road-ready diesel.

So far, biofuels have largely been limited to ethanol, which is harder to transport than petrol and is made from crop plants such as maize (corn) and sugarcane, putting vehicles in competition with hungry mouths. In this week's Nature, researchers from the University of California, Berkeley, and the biotech firm LS9 of South San Francisco, California, among others describe a potential solution: a modified Escherichia coli bacterium that can make biodiesel directly from sugars or hemicellulose, a component of plant fibre (see page 559). The method can be tailored to produce a host of high-value chemicals, including molecules that mimic standard petrol, and could be expanded to work on tougher cellulosic materials, the researchers say.

The work identifies a potentially cost-effective way of converting grass or crop waste directly into fuel, filling gas tanks without raising global food prices or increasing hunger and deforestation in far-flung locales. Moreover, the process is much more climate friendly than manufacturing ethanol from maize, and produces higher-energy fuels that are interchangeable with current petroleum products. The next step is to scale the process up and adapt it to cellulose, which makes up the bulk of plant material.

The process has a lot of promise for actually being commercialized. ,

"It's a nice milestone in the field of biofuels, and it has a lot of promise for actually being commercialized," says James Liao, a metabolic engineer and synthetic biologist at the University of California, Los Angeles.

LS9's calculations, performed with the help of the Argonne National Laboratory in Illinois, show that the biodiesel that it is preparing to market reduces greenhouse-gas emissions by 85% compared with standard diesel. That calculation is based on using Brazilian sugarcane, which is a much more efficient feedstock than maize; LS9 says that the shift from sugars to biomass as a feedstock would reduce greenhouse gases even further.

The company has been working to convert sugars into tailored molecules for several years, says co-author Stephen del Cardayre, LS9's vice-president for research and development. However, their university collaborators went two steps further, eliminating the need for additives and then folding in the ability to use hemicellulose as a feedstock. "This paper is a representation of the types of efforts that are going to move us to biomass," he says.

The researchers basically amplified and then short-circuited E. coli's internal machinery for producing large fatty-acid molecules, enabling them to convert precursor molecules directly into fuels and other chemicals. The team then inserted genes from other bacteria to produce enzymes able to break down hemicellulose. In all, the authors report more than a dozen genetic modifications.

The results could buoy LS9, says Mark Bünger, a research director at business consultancy Lux Research in San Francisco. Like its competitors, including Amyris of Emeryville, California, and South San Francisco-based Solazyme, LS9 struggled for funding in 2008 and early 2009 because of the drop in oil prices and the economic downturn, Bünger says.

But LS9 made it through, securing US$25 million in new funding from various sources, including a strategic partnership with oil giant Chevron last September. The company plans to open a commercial-scale demonstration plant later this year.

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Tollefson, J. Altered microbe makes biofuel. Nature 463, 409 (2010). https://doi.org/10.1038/463409a

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