Chemical fertilizers have significant drawbacks: producing them accounts for about 1.5% of the world’s greenhouse-gas emissions, and their long-term use eventually depletes soil nutrients. Substituting bacteria that convert nitrogen gas to ammonia could reduce those problems, but the bacteria are sensitive to heat and humidity, so it’s difficult to scale up their manufacture and ship them to farms.

Now MIT researchers have devised a self-assembling coating, combining a metal and an organic compound called a polyphenol, that protects bacterial cells from damage without impeding their growth or function. They found that bacteria encased in this coating improved the germination rate of a variety of seeds, including corn and bok choy, by 150% and ward off fungi and other pests. 

With this coating, whose components are generally recognized as safe by the FDA, delicate microbes can be dried, making them easier to distribute as fertilizers, says Ariel Furst, an assistant professor of chemical engineering and the senior author of the study.

“We can protect them from the drying process, which would allow us to distribute them much more easily and with less cost,” says Furst, who has started a company called Seia Bio to commercialize the technology. “They can also withstand heat up to 132 °F, which means that you wouldn’t have to use cold storage for these microbes.”