The current provided by oxygen-reducing microbial cathodes is related to the composition of their bacterial community.

Oxygen reducing biocathodes were formed from sludge under constant polarization at -0.2 and +0.4V/SCE. Under chronoamperometry at pH10.3 ± 0.3, current densities of 0.21 ± 0.03 and 0.12 ± 0.01 Am(-2) were displayed at -0.2V/SCE by the biocathodes formed at -0.2 and 0.4V/SCE, respectively. Voltammetry revealed similar general characteristics for all biocathodes and higher diffusion-limited current densities (0.84 ± 0.26 Am(-2)) than chronoamperometry. Up to 3.7 Am(-2) was reached under air bubbling. A theoretical model was proposed to show the consistency of the chronoamperometric and voltammetric data. The biocathodes formed at -0.2V/ECS that gave the highest electrochemical performance showed a homogeneous selection of Deinococcus-Thermus and Gemmatimonadetes, while the biocathodes formed at 0.4V/SCE were enriched in different bacteria. The biocathode that led to the worst electrochemical characteristics, while formed at -0.2V/SCE, showed the largest bacterial diversity. The biocathode performance was consequently related to the enrichment in specific microbial phyla. Moreover, the strong presence of bacteria parented to Deinococci may also have some interest in biotechnology.