A promising new system can convert fronds of brown seaweed into biofuel, opening up a new possible source of energy that could help replace fossil fuels, like gasoline. The secret: bacteria genetically engineered to break down a previously inaccessible sugar in seaweed, called alginate. The researchers who developed this new system used it to generate ethanol, a biofuel that is added to gasoline; however, it has the potential to produce not just ethanol but other biofuels, they and others say. The new system is like a Lego platform. With changes to the components in the process, the same microbe-based system could be used to produce a variety of products. 

For instance, the system could be used to turn seaweed into a source (also called a feedstock) for other biofuels, which could include butanol — an alcohol, like ethanol, that is blended into gas — or chemicals used in biodiesel, which has properties similar to conventional, petroleum-based diesel. 

Seaweed now joins the cadre of plants — from corn to single-celled algae — that offer tantalizingly renewable and domestically produced alternatives to fossil fuels. In the United States, ethanol made from corn is added to gasoline; in Brazil, cars are powered largely, sometimes completely, by ethanol made from sugar cane. But converting corn and sugar cane into fuel can be problematic, since both are also food crops. 

Even other potential biofuel sources, like switchgrass, can compete for land in a world whose population is growing and seeking a more resource-intensive diet. Seaweed — a relatively unexploited source of nutrition, is high in sugars, which are precursors for most biofuels. Seaweed also lacks lignin, a compound that makes cell walls rigid in land plants and that must be removed before such plants can be turned into fuel. Even so, until now, seaweed appeared to have limited potential as a feedstock for biofuel, since one of its primary sugars, alginate, couldn't be broken down efficiently enough to produce biofuel on an industrial scale. The bug Marine microbes already have the ability to break down alginate, transport the products and metabolize them. E. coli do something similar, spitting out ethanol at the end of a multi-step process. The last of the steps could be replaced to produce other biofuels, or even chemicals such as plastics and polymer building blocks. This system also takes advantage of other sugars in the seaweed, mannitol and glucan, since the E. coli already possessed the ability to break down mannitol, and commericially available enzymes can easily break glucan down into a more accessible form, glucose. This system could be used in any brown seaweed (seaweeds also come in green and red). 

Seaweed's advantages, its high sugar content and lack of lignin, make it a viable source for biofuel from a cost perspective. Looking ahead There is also the environmental question.  One challenge will likely be seaweed's demand for nutrients, such as nitrogen and phosphorus, which are not naturally abundant in the oceans.