Cation-driven envelope dynamics modulate outer membrane vesiculation and extracellular electron transfer in Geobacter

Geobacter bacteria use conductive pili and redox-active outer membrane vesicles to mediate metal transformations critical to the effectiveness of bioremediation and energy technologies. Mechanistic knowledge into these processes primarily comes from studies with Geobacter sulfurreducens grown in media closely formulated to mirror the mineral chemistry of contaminated sites. Although subtle differences in the media’s cationic strength did not measurably change permeability, they reprogrammed outer membrane-peptidoglycan crosslinks modulating vesiculation and envelope functions impacting growth efficiency and mineralization. Cations that strongly bind and neutralize peptidoglycan carboxylates to prevent cell wall distortions, such as sodium and uranyl ions, ultimately determined the extent of envelope remodeling and cell bias toward pili-driven mineralization or membrane adsorption and release in vesicles. These findings identify cation chemistry as a key regulator of outer membrane vesiculation and the reprogramming of envelope functions ultimately determining the reproducibility of laboratory studies and effectiveness of bioremediation and energy-harvesting applications.