Microbial fuel cells (MFCs) are an emerging technology that utilise microbes to carry out applications such as energy production and bioremediation. MFCs utilise the metabolism of electrochemically active bacteria (EAB) within the soil to generate energy as they respire by depositing electrons onto a buried anode connected to a cathode above the soil. Integrating plants into the substrate of an MFC, to make a plant microbial fuel cell (PMFC), improves on the sustainability of MFCs through the release of electron donors for EAB respiration via plant root exudates. EABs such as Geobacter sulfurreducens are typically discussed from an applied standpoint for their electron transfer mechanisms. This work sought to use a specialist/generalist paradigm to examine PMFC soil microbial communities, with a focus on EABs and their response to the manipulations of environmental resources. While classifying organisms as specialists or generalists is more common in macroecology, these concepts are equally applicable to microorganisms, and will improve our fundamental understanding of EABs, their distributions, and how to manipulate them in situ.
Bacterial communities that developed at the cathode, anode, and plant roots of PMFCs constructed using Oryza sativa were examined after 14 weeks using 16S rRNA sequencing. Each of the sampled locations were compared between open and closed circuits to investigate for selective effects on specialist EABs. By inoculating known EABs and known plant-interacting bacteria, this study also investigated the effect of specific functional groups of microbes and priority effects on microbial community structure that develops at these locations. Our study highlights EABs as specialists of their niche within the soil community, which can be enriched through the manipulation of environmental resource availability more effectively than reliance on priority effects via inoculation. Furthermore we discuss how PMFC communities using the ecological concepts of specialists and generalists presents us with a useful tool in the discussion of the assemblage of microbial communities in the environment.