Electro-driven methanogenic microbial community diversity and variability in the electron abundant niche

The underlying dynamics of microbial (bacteria and archaea) communities ecologically responding to an applied potential are critical to achieving the goal of enhancing bioenergy recovery but are not sufficiently understood. We built a MEC-AD mode that increased methane production rate by several times (max. 3.8 times) during the startup period compared to control AD, changed the absence or presence of external voltage to provide the pre-, dur-, and post- samples for microbial analysis. From a time and spatially dependent community analysis of electrode-respiring bacteria and methanogens, the corresponding Geobacter developed under the influence of external voltage, pairing with methanogens in the anodic and cathodic biofilm to generate methane. Additionally, at the cathode, the Alkaliphilus (basophilic bacteria) also correspondingly shifted alongside the change of external voltage. The mcrA sequencing confirmed a change in the dominant microbe from acetoclastic (mostly Methanosarcina mazei LYC) to hydrogenotrophic methanogens (mostly basophilic Methanobacterium alcaliphilum) at the cathode with 0.8 V voltage. Overall, the external voltage not only enriched the functional microbes including electrogens and methanogens but also indirectly shifted the composition of the bacterial and archaeal community via disturbing the pH condition. The predictive functional profiling indicated that the cathodic methanogenesis principally followed the metabolism pathway of the hydrogenotrophic methanogens, suggesting the F420 co-enzyme could be the key mediate for electron transfer. All data suggested that the electric stimulation would change and maintain the micro-environmental conditions to shift the bacterial/archaeal community.