Legumes benefit from mutualistic symbioses with Rhizobia bacteria, which are induced to fix nitrogen when inside of the nodules produced by the plant. Cereals also associate with Rhizobia, but without nodules they don’t fix nitrogen. Ryu et al. set out to engineer inducible nitrogenase activity in free-living Rhizobia and other bacteria that associate with cereals. They introduced natural and engineered nitrogen fixing (nif) gene clusters from several different bacteria sources into cereal-associating bacteria. Some operons were engineered to remove inhibition by ammonium (the end-product of nitrogenase), and some were engineered to be induced by synthetic genetically encoded sensors. In the presense of plants that activate these sensors, nif transcription is induced. Some of these studies led to bacteria that are able to fix nitrogen in the presence of plants, a first step in building strains that can efficiently deliver fixed nitrogen to cereals. (Summary by Mary Williams) Nature Microbiol. 10.1038/s41564-019-0631-2