This study examined the changes in microbial diversity in response to different electrode materials viz., stainless steel mesh (SS) and graphite plate as anodes in two microbial electrolysis cell (MEC) each poised at 0.2 V, 0.4 V, 0.6 V and 0.8 V. Changes in microbiota prior to and after pretreatment along with microbiota enriched in response to various poised potentials with SS and graphite are monitored by 16S rRNA gene based DGGE profiling. Significant shifts in microbial community were noticed at all these experimental conditions. Correspondingly, the level of hydrogenase belonging to genera Bacillus, Pseudomonas, Rhodopseudomonas and Clostridium was studied by quantitative real time PCR (RT-PCR) at various applied potentials. DGGE based 16S rRNA gene profiling revealed enriched members belonging to phylum Firmicutes predominantly present at 0.8 V in both MECs contributing to high hydrogen production. This study first time explored the growth behavior of mixed consortia in response to poised potentials and electrode materials. (C) 2015 Elsevier Ltd. All rights reserved.