Nitrogen fixation (from N2 to NH4) is the first step in the transformation of atmospheric nitrogen into nitrogen that can be assimilated by living organisms. This reaction is catalysed by so-called diazotrophic microorganisms that reduce atmospheric nitrogen into ammonia to fuel their growth. Biomass production by N2 and CO2 fixation via electrostimulation in a microbial electrochemical system has been shown recently (Rago et al. 2019). We propose to investigate enrichment strategies allowing the selection of a cathodic biofilm capable of growing from the present gases and a mineral energy supply.