2014 was a banner year for making automotive fuel from nonfood crops, with a series of major new production plants opening in the United States. However, producing this so-called cellulosic ethanol remains considerably more expensive than gasoline. So researchers are always on the lookout for new ways to trim costs. Now they have a new lead, a microbe that can use abundant nitrogen gas as the fertilizer it needs to produce ethanol from plants. The discovery is “a major commercial accomplishment for biofuel production,” says Steven Ricke, a microbiologist, and editor of a textbook on biofuel production at the University of Arkansas, Fayetteville, who was not involved in the study. Scientists have long eyed biofuels as a cleaner and more sustainable alternative to traditional fossil fuels. Instead of pumping oil from the ground, researchers harvest plants like cassava and sugarcane, grind them up, add enzymes to break down the plant matter and sprinkle in the yeast. The microbe ferments sugars in the plants to produce ethanol, a form of alcohol, which is now commonly mixed with gasoline and used in cars and buses around the world. But biofuels are controversial. The majority are derived from food crops, like corn. Critics say the increased demand for these crops could increase food prices. And although direct emissions of carbon dioxide from burning biofuels are less than those from traditional fuels, some scientists now argue that once indirect emissions from land use change and production of the crop are considered, the overall emissions from some biofuels can actually be higher. So in recent years, researchers have turned to nonfood crops—like trees and bamboo for biofuel production. These crops need less fertilizer than traditional biofuel crops, and they often have a less detrimental impact on the land. In an ideal world, biofuels would be produced only from plant materials that cannot be eaten, such as trees and parts of plants that are left in fields after harvest, like straw. But there are problems. The enzymes needed to break down plants’ primary structural components cellulose and hemicellulose into simple sugars is expensive. To ferment the simple sugars, the microbes also need nitrogen to grow and divide. So researchers add fertilizer to their fermentation vats to boost the ethanol yields. It is estimated that an ethanol production plant may be spending more than $1 million on this a year. Instead of using yeast to ferment their plants into fuel, microbiologists at Indiana University, Bloomington, turned to Zymomonas mobilis, a bacterium also capable of doing the job. So the researchers looked at the amount of ethanol that the microbe could produce with and without additional nitrogen fertilizer being supplied and found that it did better without it. The study, published in the Proceedings of the National Academy of Sciences, even showed that the bacterium produces ethanol more quickly and uses more of the plant material when it uses nitrogen gas than when it is fed nitrogen in fertilizer. If the same holds true in a production plant, this could reduce biofuel production costs, the authors say.