Modified 'bugs' turn seaweed into fuel
From ocean to tank Scientists have genetically engineered microbes to process brown seaweed into biofuel.
The work by researchers including Dr Yasuo Yoshikuni from Seattle's Bio-Architecture Lab could see large underwater farms become a source of renewable energy.
Scientists focused on brown seaweed because its high sugar content provides a good biomass, and the seaweed doesn't compete with food crops for land and fresh water.
However Yoshikuni says, "The seaweed uses a different type of carbohydrate called an alginate which can't be broken down by the land based E. coli bacteria normally used in industry".
"This bottleneck means biofuel from seaweed is too expensive to compete with regular petroleum-based fuels," says Yoshikuni.
To overcome the problem, Yoshikuni and colleagues examined a marine microbe called Vibrio splendidus, which naturally metabolises and consumes seaweed in the ocean.
"We don't know if we can scale up these microbes so we genetically engineered terrestrial E. coli microbes instead," says Yoshikuni.
Reporting in the journal Science, Yoshikuni and colleagues successfully isolated a 36,000 base pair DNA fragment from V. splendidus which encodes enzymes that metabolise alginate.
"Using synthetic biology and enzyme engineering, the DNA strand was spliced into the E. coli bacteria, which was then able to digest the sugar polymers in the seaweed converting them into ethanol," says Yoshikuni
The researchers say if this process can be successfully scaled-up, seaweed could help meet the growing demand for sustainable fuel.
According to Yoshikuni there are already commercial processes for aqua farming of seaweed especially in Asia with 15 million tonnes produced annually.
"Using three per cent of the world's coastlines we can replace five per cent of total oil consumption. That's 60 billion gallons of fuel"
Yoshikuni says it would be grown on long submerged ropes.
"We seed the juvenile seaweed onto long ropes which are dangled into the sea and the seaweed grows on these ropes getting all its nutrients from the sea and Sun," says Yoshikuni. "The harvested seaweed would be fed to the genetically engineered E. coli, with the ethanol refined in a similar way to existing processes."
"We are currently looking into the environmental impact of the project on a commercial scale."
Yoshikuni says seaweed also absorbs industrial waste such as phosphorus and nitrogen, which can help reduce the incidence of algal blooms.
"We believe seaweed is green energy and can become the most sustainable and upscaleable biomass for the next generation."