Polarized potential and electrode materials implication on electro-fermentative di-hydrogen production: Microbial assemblages and hydrogenase gene copy variation

Schematic representation of the MEC reactor used in the present study (a) MEC reactor operated with graphite plate as both anode and cathode electrode materials, (b) MEC reactor operated SS-mesh as anode and graphite as cathode electrode material. [Display omitted] •SS anode performance was compared with graphite at different potentials in MEC.•CHP and VFA production was high using SS anode at an applied potential of 0.8V.•Firmicutes were predominant at an applied voltage of 0.8V in both the reactors.•hydA gene copies of genus Clostridium were high at 0.8V in both MEC reactors. 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 0.2V, 0.4V, 0.6V and 0.8V. 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 0.8V 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.