Bacterial Vesicles Mediate Extracellular Electron Transfer

Many Gram-negative bacteria are known to release outer membrane vesicles (OMVs) into the surrounding environment during normal growth; OMVs perform diverse biological and environmental functions (e.g., virulence factor transport, horizontal gene transfer, quorum signaling, cellular defense, and cell-to-cell communication). However, the production of OMVs has not been reported in Geobacter species, and their role in extracellular electron transfer (EET) is unknown. Here, we demonstrate, for the first time, that Geobacter sulfurreducens releases OMVs containing abundant cytochromes that can promote EET from microbial cells to an anode. OMVs released by Geobacter cells not only promote exoelectrogen EET (1.73-fold higher current density in Shewanella oneidensis MR-1) but also confer electrogenic ability to non-exoelectrogens (G. sulfurreducens mutant strain ΔomcZ and Escherichia coli). These functions are mainly attributed to the abundance of c-type cytochromes bound on or entrapped in OMVs. Our findings suggest that redox-active OMVs can serve as shared mediators facilitating EET in natural ecosystems, representing an ecologically important but overlooked biological electron transfer process.