11.4 Nanowire-Producing Bacteria: Taxonomy, Description, and

nanowire Production

11.4.1 Description of the Genus Geobacter

The Geobacter species belong to the Geobacteraceae family, which are Gram-negative, rod-

like, non-spore-forming, anaerobic, classified into three phylogenetic clades, and have the

G. metallireducens strain type. The two most studied Geobacter species are G. metallireducens

and G. sulfurreducens and play an important role in the bioremediation process. The

Geobacter species were considered the first ones described to use hydrogen as an electron

donor [28].

11.4.2 Description of the Genus Shewanella

The genus Shewanella, belonging to the Shewanellaceae family [29], was described first in

1931 by Derby [30,31]. They are Gram-negative, rod-shaped, non-spore-forming, fa­

cultatively anaerobic, and aerobic. They do not form endospores or microcysts and are

chemo-organotrophic, oxidase-positive. This bacteria is commonly found in aquatic ha­

bitats. The genus includes around 70 species and the type of species is S. putrefaciens.

11.4.3 Nanowire Formation and Structure

Bacterial nanowires have been involved in EET. The structure and composition of bacterial

nanowires are diverse depending on the species. Geobacter nanowires anchored in outer

membrane cells are essential for the electron transfer among G. sulfurreducens and to Fe(III)

oxides [21]. Their conductivity can be attributed to the two models of electron transfer

such as hopping or a metallic-like mechanism [32]. The microbial nanowires of S. oneidensis

FIGURE 11.3

Bacterial extracellular electron transfer EET. (a) Schematic representation of proposed mechanisms of electron

transfers from microbes to the anode: a. Mediator transfer, b. Direct transfer, c. Nanowires transfer. Reprinted

with permission [ 3]. Copyright © 2015, Elsevier. (b) Type of bacterial EET mechanisms of Geobacter and

Shewanella. (I) The OMC-based DET conduit in Geobacter; (II) bacterial nanowire; (III) electron transfer in

Shewanella including flavins and CTCs; (IV) electrode respiration-coupled proton motive force and energy

(ATP). Reprinted with permission [ 26, 27]. Copyright ⓒ 2012 Elsevier.

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