Paraclostridium sp. AKS46 vesicles facilitate extracellular electron transport.

Aims: Paraclostridium sp. AKS46 was shown to have high exoelectrogenic activity. The current study investigated whether membrane vesicles (MVs) contribute to electrogenic activity of this organism.

Methods and results: To examine the contribution of MVs to electrogenic activity, formation of MVs was first investigated by microscopic analyses of AKS46 cells at different time points of growth. The results showed increasing MV formation with time, especially in electrode-attached cells. To test electrogenic activity, the redox property and the electrochemical activity of the vesicles were examined. To this end, purified AKS46 vesicles demonstrated robust redox activities, and cyclic voltammetry and electrochemical impedance spectroscopy revealed high electrochemical properties of purified vesicles. Furthermore, proteomic analysis of the vesicles identified the presence of redox-active proteins, particularly flavoproteins, which might significantly contribute to electron carrier properties. AKS46 MVs also harbour enzymes involved in CO2 and nitrogen fixation, suggesting their roles in nutrient cycling and maintaining microbial ecology.

Conclusion: The exoelectrogenic gram-positive bacteria Paraclostridium sp. AKS46 produces extracellular vesicles packed with electron-rich molecules and thus, these vesicles act as electron transporters. The work highlights a vesicle-mediated mechanism for energy harvesting from waste degradation in microbial fuel cells.