a, b, Strategy to evaluate the effect of an electric field on the production of OmcZ nanowires. Wild-type G. sulfurreducens cells were grown with a continuous supply of fumarate on graphite electrodes as anodes in a microbial fuel cell. a, An electric field was supplied during the growth of current-producing biofilms by connecting anode to cathode via a potentiostat. b, The electric-field was absent after disconnecting the anodes from the cathodes. OmcZ peptide coverage (blue) in filament preparations of c, Wild-type (WT) and d, W51W57 strain confirming the presence of an extracellular (30 kDa) form of OmcZ that forms nanowires. Comparison of OmcZ abundance in filament preparations of WT and W51W57 strains using e, Immunoblotting and f, Mass spectrometry showing higher level of OmcZ in W51W57 strain than WT. Data represent mean ± standard deviation (n = 3 biologically independent samples overlaid as black circles).