Direct interspecies electron transfer mediated by magnetotactic bacteria

Direct interspecies electron transfer (DIET) enables microorganisms to exchange electrons directly, without relying on traditional intermediates like hydrogen or formate in anaerobic methanation. The DIET stimulation in bioreactors typically relies on conductive materials, such as biochar, activated carbon or iron oxides, to facilitate electron flow between microbial partners. 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. In this study, Desulfovibrio magneticus , a magnetotactic bacterium capable of producing intracellular magnetic nanoparticles, was identified in co-existence with Geobacter from a non-conductive sand-bed Anaerobic Fluidized Bed Reactor (AFBR) treating low-strength sewage. Metagenomic, metatranscriptomic and physical characterization analyses suggest a potential mechanism, in which magnetotactic bacteria may contribute to syntrophic DIET interaction with exoelectrogenic bacteria and electrotrophic methanogens, such as Methanobacterium , possibly mediated by the production of magnetic nanoparticles. Magnetic characterization revealed a higher saturation and remanent magnetization in the AFBR sand compared to the control, indicating enrichment of ferrimagnetic minerals within the reactor bed. The hysteresis behavior was consistent with a dominant contribution of pseudo-single domain particles, suggesting the presence of fine magnetic phases in the system. This association may represent an adaptive strategy to overcome energetic limitations and enhance syntrophic cooperation in environments lacking conductive materials. These findings highlight a previously unexplored possibility and emphasize the need for further investigation into its underlying mechanisms, regulatory processes, and potential biotechnological applications. © 2026 The Authors.