Magnetotactic bacteria mediate Direct Interspecies Electron Transfer

Microbial cooperation is essential in anaerobic digestion, enabling communities to process organic matter in a collaborative chain. In energy-limited environments, microorganisms develop novel interactions to optimize resource utilization, including syntrophic relationships that facilitate electron transfer. Direct interspecies electron transfer (DIET) is an alternative mechanism to overcome these limitations and this process typically requires conductive materials to facilitate electron flow. Geobacter is the most well-known exoelectrogenic bacterium capable of performing DIET and its prevalence in low-strength systems, despite the absence of conductive material, is intriguing and remains unclear. Surprisingly, Desulfovibrio magneticus - a magnetotactic bacterium capable of producing intracellular magnetic nanoparticles - was identified in samples from the Anaerobic Fluidized Bed Reactor (AFBR). Here, we propose a potential syntrophic relationship between magnetotactic and exoelectrogenic bacteria, possibly extending to methanogens known for their involvement in DIET, such as Methanobacterium. This hypothesis is grounded in previous research indicating that magnetite nanoparticles can enhance DIET interactions. By combining metagenomic, metatranscriptomic and physical characterization analyses, our results unveil an unprecedented possibility: magnetotactic bacteria producing magnetite nanoparticles to engage in DIET. Magnetic susceptibility measurements confirm the presence of magnetite nanoparticles within the AFBR sand bed, a signature absent in the control sand, reinforcing that DIET occurred in a non-conductive environment mediated by magnetotactic bacteria. This syntrophic relationship may have occurred due to the energy limitations in such a low-strength system. These findings introduce the emerging field of Microbial Electromagnetism, emphasizing the need for further investigation into its underlying mechanisms, regulatory processes, and potential biotechnological applications.