Brown seaweed’s potential as a vast source of biofuels has been highlighted with the announcement that scientists have found a way of converting all its major sugars into ethanol.
A team reported in Science today (19 January) that it has engineered a microbe that will convert the sugars to ethanol, overturning one of the main obstacles to making the use of brown macroalgae, or seaweed, as a biofuel feedstock competitive.
The prospective ethanol yield from brown seaweed is approximately two times higher than that from sugarcane and five times higher than maize, from the same area of cultivation.
But its full potential cannot be reached because of the inability of industrial microbes to break down alginate, one of the three most abundant sugars in brown seaweed, commonly known as kelp, which is the most widely grown seaweed in the world.
Now, researchers based in Chile, France and the United States say that they have developed the first microbe capable of fermenting all the major sugars found in a common species of brown seaweed (Saccharinna japonica).
“This [development] makes [brown seaweed] a viable biomass for the production of renewable fuels and chemicals,” Yasuo Yoshikuni, co-author of the study and chief science officer at Bio Architecture Lab (BAL) Inc — a US company that has built four seaweed farms off the coast of Chile — toldSciDev.Net.
The team engineered Escherichia coli bacteria, which has the natural ability to metabolise glucose and mannitol — the other two main sugars in brown seaweed — and Vibrio splendidus a microorganism containing all necessary genes to metabolise alginates.
As a result, the scientists were able to get a yield of bioethanol directly from seaweed equivalent to 15,000-20,000 litres per hectare per year.
An analysis by the US Department of Energy has previously reported that, if technical barriers were overcome, brown macroalgae could produce 19,000 litres per hectare per year.
Brown seaweed “does not compete with food crops or terrestrial plants for land and fresh water, and seaweed aquafarming can absorb excess nutrients in the ocean [which can cause oxygen depletion]”, said Yuki Kashiyama, head of BAL Chile.
Stephen Mayfield, director of the San Diego Center for Algae Biotechnology at the University of California, San Diego, United States, told SciDev.Net: “This is a great engineering feat but, at least for right now, kelp is not a viable feedstock for ethanol production, and won’t be until we can figure how to grow it and transport it to a processing site in an easy and energy efficient way”.
According to Yoshikuni, to demonstrate “overall process economics more in depth” an experimental pilot facility is being built in Chile and is scheduled to start scaling up the process by July. For this stage BAL has received a grant from CORFO (see Chile is committed to algae-based biofuels, in Spanish), the Chilean agency that promotes innovation.
