barrier from one side to the other side without requiring nuclear movement. It is due to

the formation of a complex structure with different functional groups.

11.5.3 Metal-Like Conductivity by G. Sulfurreducens Nanowires

Nanowire conductivity was the first discovery in G. sulfurreducens and some of Geobacter

species [21]. The mechanism of transfer electron of Geobacter spp. nanowires are sug­

gested by a metallic-like conductivity. In the metal-like conductivity (Figure 11.5), there is

a dependence on the cytochromes, which is a condition that differs from the electron

hopping mechanism. However, the nanowires of G. sulfurreducens can promote electron

transfer to the cell that follows up to Fe (III). Yet, several components have been identified

which include c-type cytochrome located in the inner as well as an outer membrane

which are associated with the pili [35,36]. Alongside that, a study conducted by El-

Naggar et al. [34] demonstrated that the electric conduction along bacterial nanowires of

S. oneidensis MR-1 can occur through EET. The nanowires of G. sulfurreducens consist

of PilA. Also, homology with PilA in Gram-negative bacteria is related to the production

of type IV pili. This PilA subunit of pilin from G. sulfurreducens contains five conserved

aromatic amino acids that can play a role in long-distance electron transfer [37].

Generally, the conductivity of G. sulfurreducens nanowires can increase exponentially

upon cooling and low pH of around 2 [38]. In conclusion, the different studies published

demonstrated that the electron transfers in microbial nanowires of G. sulfurreducens

proposed the metal-type conduction instead of the electron hopping model.

11.6 Biotechnological Application of Microbial EET

The discovery of mechanisms of microorganisms with electron transfer capability has been

explored in many fields of biotechnology application and bioengineering. In this part, we

developed the field in which these microbes have been explored for applications such as

bioremediation of environmental contaminants, bioelectricity, and bioenergy production.

FIGURE 11.5

Electron current model along bacterial nanowires. (a) Electron hopping and S. oneidensis filaments model’s (b)

metallic-like conduction for G. sulfurreducens pili. Reprinted with permission from [ 23]. Copyright © 2013 Elsevier.

Microbial Nanowires

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