Scientists have devised a new way to produce ethanol directly from seaweed, offering the potential to generate biofuels that don’t compete with terrestrial food production and won’t suck up scarce freshwater, reports a study published today in Science.
Researchers from the Bio Architecture Lab in Berkeley, California engineered E. coli bacterium to digest brown seaweed and produce ethanol as a byproduct. Kelp, which grows up to a meter a day and is abundant in temperate coastal regions, is a type of brown seaweed.
Photo by: Rhett A. Butler.
“BAL’s technology to ferment a seaweed feedstock to renewable fuels and chemicals has suggested an entirely new pathway for biofuels development, one that is no longer constrained to terrestrial sources,” said Jonathan Burbaum of the U.S. Department of Energy’s Advanced Research Projects Agency, which helped fund the research. “When fully developed and deployed, large scale seaweed cultivation combined with BAL’s technology promises to produce renewable fuels and chemicals without forcing a tradeoff with conventional food crops such as corn or sugarcane.”
Scientists have long struggled to produce ethanol from seaweed. The stumbling block was alginate, one of four kinds of sugars produced by seaweed. Alginate — a complex polysaccharide — is difficult for microbes to breakdown. The breakthrough came when the researchers identified a biochemical pathway used by Vibrio splendidus, a marine microbe that feeds on brown seaweed, and inserted the responsible genes into a strain of E. coli. The bacterium was designed to convert the seaweed sugars directly into ethanol.
“About 60 percent of the dry biomass of seaweed are fermentable carbohydrates, and approximately half of those are locked in a single carbohydrate – alginate,” said Daniel Trunfio, Chief Executive Officer at Bio Architecture Lab, in a statement. “Our scientists have engineered an enzyme to degrade and a pathway to metabolize the alginate, allowing us to utilize all the major sugars in seaweed, which therefore makes the biomass an economical feedstock for the production of renewable fuels and chemicals.”
The study estimates that seaweed growing in less than 3 percent of the planet’s coastal waters could produce enough ethanol to replace over 60 billion gallons of fossil fuels. It notes that large-scale seaweed production is already common around the world.
But what isn’t clear is whether seaweed-based biofuels could have unintended and adverse effects on marine ecology. Many land-based biofuels once touted as clean energy solutions — palm oil, corn, rapeseed, jatropha, sugar cane, and soy, to name a few — have been subsequently found to have substantial environmental impacts, including driving deforestation and spawning water and air pollution.
CITATION: Adam J. Wargacki et al. An Engineered Microbial Platform for Direct Biofuel Production from Brown Macroalgae. Science 20 January 2012: Vol. 335 no. 6066 pp. 308-313 DOI: 10.1126/science.1214547