Methods and systems for producing a biofuel using genetically modified ammonia-oxidizing bacteria (AOB) are disclosed. In some embodiments, the methods include the following: providing an AOB that have been genetically modified to include a particular metabolic pathway to enable them to generate a particular biofuel or chemical; feeding a first source of ammonia to the AOB; feeding carbon dioxide to the AOB; and producing at least the biofuel or chemical, nitrite, and an AOB biomass. In some embodiments, the methods and systems include the following: a bioreactor including AOB that have been genetically modified to include a particular metabolic pathway to enable them to generate a particular biofuel; a first source of ammonia; a source of carbon dioxide; and a electrochemical reactor that is configured to electrochemically reduce nitrite produced in the bioreactor to a second source of ammonia.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under DE-AR0000060 awarded by Advanced Research Projects Agency of the Department of Energy. The government has certain rights in the invention.