Systems and methods for fixing carbon using bacteria are described. In one embodiment, a system includes a reactor chamber with a solution contained therein. The solution may include hydrogen (H2), carbon dioxide (C02), bioavailable nitrogen, and a chemolithoautotrophic bacteria. The system may also include a pair of electrodes that split water contained within the solution to form the hydrogen. Additionally, the system may be operated so that a concentration of the bioavailable nitrogen in the solution is below a threshold nitrogen concentration to cause the chemolithoautotrophic bacteria to produce a product.