THE tree was a black cottonwood and it grew by the banks of the Nisqually river in Washington State. The tree is gone now, swept away by the shifting river, but not before Gerald Tuskan of Oak Ridge National Laboratory in Tennessee and his team made history last year by sequencing its genome – a first for any tree species.
While the feat may seem like an odd achievement for a lab that was originally created for the Manhattan Project – the American-led effort to develop an atom bomb – it is somehow fitting. Like the bomb, the tree is meant to help the US gain strategic leverage, though this time through energy independence.
“The big push is to displace imported oil,” says Tuskan. “The question is, can we produce ethanol cheaply enough to do that.” By tinkering with the black cottonwood’s genome, researchers have already produced variants with thicker stems and shallower root systems in the hope of engineering a more harvestable form of biomass for conversion to ethanol. The approach even resembles that of the Manhattan Project in that it embraces the revolutionary advances in the science of its era: physics then and biotechnology now.
Advertisement
Ethanol has long been touted in the US as an environmentally friendly alternative to petroleum. In practice, however, it has proved to be anything but. The reason is that in the US ethanol for fuel is currently produced from corn – a crop that requires intensive farming, chemical fertilisers and plenty of water. Critics argue that growing corn for ethanol simply trades one environmental crisis for another while driving up the price of an international staple.
To escape the problem, says Nobel laureate Stephen Chu, director of the Lawrence Berkeley National Laboratory (LBL) in California, ethanol producers must forgo the easily fermented sugar and starch in corn and switch to plants that can be harvested for cellulose. “The potential yield that we have from converting cellulose to biofuel could be five or 10 times greater than what we have for corn,” says Chu. Depending on the conditions, the ideal cellulose-rich crop would be a variant of a swift-growing tree such as the cottonwood, or a tall grass such as those of the genus Miscanthus.
“The potential yield that we have from converting cellulose to biofuel could be five or 10 times greater than that of corn”
To facilitate the efficient breakdown of cellulose, Melvin Simon of the California Institute of Technology in Pasadena has been studying how termites do it so well. Working with the US Department of Energy’s Joint Genome Institute in Walnut Creek, California, Simon has sequenced the genes of bacteria that live in the termite’s gut and has now uncovered genetic instructions for creating wood-dissolving enzymes that he thinks could be optimised for biofuel production. “Microbes have had a billion years to try every means of energy conversion,” says Simon. “We have barely touched the potential in that diversity.”
This new ferment across the spectrum of biofuel research was apparent in discussions at this week’s meeting of the American Association for the Advancement of Science in San Francisco.
