Extracellular electron uptake by Geobacter from solid donors: Biocorrosion and biohybrid systems

Electroactive Geobacter cells can gain electrons from solid donors to drive their metabolism. These donors include cathodes of bioelectrochemical systems, metallic surfaces, other microbial cells, conductive particles, semiconductors, piezoelectric materials, and dead biomass. Through extracellular electron uptake (EEU), Geobacter spp. corrode metals and damage man-made infrastructures. On the positive side, EEU can be the core of several applications, such as pollutant degradation and the bioproduction of value-added chemicals from renewable energy sources. At the molecular level, EEU by Geobacter is either direct through the physical contact of cellular components anchored on the cell surface or mediated by electron shuttles such as H₂ and riboflavin. Cell debris and outer membrane vesicles may also participate in EEU. This review examines the importance of EEU by Geobacter species in nature, for biocorrosion, and in hybrid biosystems developed for environmental engineering and biotechnological purposes. It also explores the different molecular mechanisms responsible for this physiological capacity in Geobacter.