Anode surface bioaugmentation enhances deterministic biofilm assembly in microbial fuel cells

Microbial fuel cells (MFCs) are devices that can generate energy while aiding biodegradation of waste through the activity of an electroactive mixed biofilm. Metabolic cooperation is considered essential for MFCs efficiency, especially during early-anode colonization. Yet, the specific ecological processes that drive the assembly of an optimized anode-attached community remain unknown. Here, we show, using 16S rRNA gene amplicon and shotgun metagenomic sequencing that bioaugmentation of the anode surface with an electroactive consortium originating from a well-established anodic biofilm, dominated by different Desulfuromonas strains, resulted in an extremely rapid voltage generation (reaching maximal voltage within several hours). This was in sharp contrast to the highly stochastic and slower biofilm assembly that occurred when the anode-surface was not augmented. By comparing two inoculation media, wastewater and filtered wastewater, we were able to illustrate two different "source-communities" for newly arriving species that with time colonized the anode surface in a different manner and resulted in dramatically different community assembly processes. Remarkably, an efficient anode colonization process was obtained only if unfiltered wastewater was added, leading to a near-complete replacement of the bioaugmented community by Geobacter lovleyi. We propose that anode bioaugmentation reduced stochasticity by creating available niches that were quickly occupied by specific newly-arriving species that positively supported the fast establishment of a highly-functional anode biofilm.