Geobacter

Geobacter is a genus of Gram-negative, anaerobic bacteria in the family Geobacteraceae. Members are commonly found in soil, freshwater sediments, and subsurface environments, especially at redox interfaces where insoluble metal oxides such as ferric iron are present.

Geobacter species are dissimilatory metal-reducing bacteria, meaning they generate energy by transferring electrons to external metal oxides rather than to soluble oxygen. They can couple the oxidation of organic compounds or hydrogen to the reduction of metals such as Fe(III), Mn(IV), uranium(VI), and other metals. This extracellular electron transfer is facilitated by outer-membrane c-type cytochromes and, in some species, electrically conductive pili known as nanowires.

Notable species include Geobacter sulfurreducens, a model organism for studying extracellular electron transfer; Geobacter metallireducens, capable of oxidizing a range of organic substrates with Fe(III) as the electron acceptor; and Geobacter uraniireducens, which can reduce uranium(VI). Ecologically, Geobacter contributes to the cycling of iron and other metals in sediments and can influence contaminant mobility in subsurface environments.

Applications of Geobacter include bioremediation, particularly of uranium and other metal contaminants, and the development of bioelectrochemical systems such as microbial fuel cells, where they generate electricity by transferring electrons to electrodes. Morphologically, Geobacter species are typically rod-shaped and can be motile by flagella; many are strict or facultative anaerobes.

Genomic studies have revealed extensive pathways for extracellular electron transfer and a diversity of metal-reducing strategies, underscoring Geobacter’s importance in environmental microbiology and biotechnology.