Biofuel from beneath the Waves
Bioengineers have devised a way to produce ethanol from seaweed, laying the groundwork for a biofuel that doesn’t sacrifice food crops.
Yasuo Yoshikuni and his colleagues at the Bio Architecture Lab in Berkeley, California, engineered the bacterium Escherichia coli so that it could digest brown seaweed and produce ethanol.
Many researchers are exploring ways to produce ethanol without using food crops such as sugar cane or maize (corn), and have turned to different feedstocks including switchgrass, the succulent plant jatropha, cyanobacteria and green algae. However, producing biofuels from sugar cane or maize not only detracts from food supplies, but also takes up huge areas of arable land. In the case of maize, more energy is required for growing and harvesting the crop than can be gained from the ethanol produced.
But producing biofuels from seaweed has so far proved difficult for bioengineers. Seaweed produces four kinds of sugars — laminarin, mannitol, alginate and cellulose. The biggest fraction in brown seaweed is alginate, which is a complex polysaccharide and tricky for microbes to digest.
So using Vibrio splendidus, a marine microbe that can digest brown seaweed, Yoshikuni and his team isolated a biochemical pathway that breaks down alginate. They inserted the genes responsible into a strain of E. coli, which could then digest the alginate into simple sugars. The team also engineered the strain so that it could convert those sugars into ethanol, enabling the direct production of ethanol from brown seaweed. This strain of E. coli could, in theory, be engineered to produce a variety of other useful chemicals and fuels.