Much of the dry biomass in seaweed is locked up in the form of sugars such as alginate, mannitol and glucan that most industrial microbes cannot metabolize. In a feat of genetic engineering, Wargacki et al. have succeeded in creating a strain of Escherichia coli capable of converting a large bulk of this sugar into the biofuel ethanol. Most of this inaccessible sugar is present as alginate, a linear copolymer of two uronic acids. To metabolize alginate into ethanol, the researchers expressed over 20 new genes from three different species (Vibrio splendidus 12B01, Pseudoalteromonas sp. A1 and Agrobacterium tumefaciens) in E. coli and deleted seven endogenous genes to ensure efficient fermentation into ethanol rather than other by-products. Using culture techniques that do not require any chemical, thermal or enzymatic pretreatments before fermentation, the authors achieved an ethanol titer of almost 5% volume/volume, reaching yields of over 80% of the maximum theoretical yield based on the sugar composition in seaweed. Seaweed is an especially attractive feedstock for biofuel production because its cultivation does not take valuable farmland away from other crops. (Science 335, 308–313, 2012)