Evidence of competition between electrogens shaping electroactive microbial communities in microbial electrolysis cells

Abstract

In single-chamber microbial electrolysis cells (MECs), organic compounds are oxidized at the anode, liberating electrons that are used for hydrogen evolution at the cathode. Microbial communities on the anode and cathode surfaces and in the bulk liquid determine the function of the MEC. The communities are complex, and their assembly processes are poorly understood. We investigated MEC performance and community composition in nine MECs with a carbon cloth anode and a cathode of carbon nanoparticles, titanium, or stainless steel. Differences in lag time during the startup of replicate MECs suggested that the initial colonization by electrogenic bacteria was stochastic. A network analysis revealed negative correlations between different putatively electrogenic Deltaproteobacteria on the anode. Proximity to the conductive anode surface is important for electrogens, so the competition for space could explain the observed negative correlations. The cathode communities were dominated by hydrogen-utilizing taxa such as Methanobacterium and had a much lower proportion of negative correlations than the anodes. This could be explained by the diffusion of hydrogen throughout the cathode biofilms, reducing the need to compete for space.

Effect of anode material and dispersal limitation on the performance and biofilm community in microbial electrolysis cells

“…The build-up of organic material by the previous bacteria that tried to colonize the surface allows for subsequent bacteria to attach without being pierced by the sharp graphene flakes [ 52 , 53 ]. The variation can also be explained by the stochastic process involved in the initial colonization of the surface [ 54 ]. Some studies have shown the importance of stochastic processes in the community assembly within MECs [ 12 ] and in other systems such as anammox biofilms [ 55 ].…”

The Bioaugmentation of Electroactive Microorganisms Enhances Anaerobic Digestion

“…The abundance of the potentially electroactive bacteria, including Sphingobacterium, Vagococcus, Peptoniphilus, Alkaliphilus, and Lactobacillus, in the microbial community was in good agreement with the redox peak heights in the CV (Figure 4d), and this was sufficient to demonstrate the contribution of DIET to methanogenesis in the HAD. However, among these abundant genera, while Schaalis, which belongs to the phylum Actinomycetota, has an as-yet undefined function, Sedimentibacter is known to produce acetic acid or butyrate through fermentation [42]. The high anaerobic digestion performance observed in the bio-augmented HAD appears to be a synergistic effect of fermenting and electroactive bacteria.…”