N. gonorrhoeae, Legionella pneumophila, enteropathogenic E. coli (EPEC), and Gram-positive

species. Type IV pili can present a 6 nm diameter and up to some µm in length. The T4P are

subdivided into three subtypes: T4aP, T4bP Tad pili, and T4cP designated recently based on

a sequence of amino acids of pilin [19]. The type IVa pili (T4aP) are long, straight, and

present polar bundles characterized by the existence of a PiT retraction ATPase and are

associated with enteric pathogens [20]. The type IVbP is present in between 180–238 amino

acids and has a signal peptide of 15–30 amino acids leader sequence. Many important

biological functions have been attributed to the T4P in Gram-negative bacteria such as

adherence to host cells, pathogenesis, formation of biofilms and microcolony, auto-

aggregation, and electric transfer as nanowires (Figure 11.2) [19,21]. They are considered

important virulence factors for many human and animal pathogens. In addition, the T4P

carries out another function, which is related to locomotion, termed twitching and gliding

motility in many bacterial species [22].

11.3 Microbial Nanowires and Bacterial Extracellular Electron

Transfer (EET)

In 2005, Reguera et al. [23] described the “microbial nanowire,” for the first time in mi­

crobiology literature. The bacterial nanowires are considered an important component in

microbe-electrode and microbe-microbe electron exchange. The microbial nanowires rang

up tens of µm long and facilitated long-range EET (Figure 11.3). In the field of electro­

microbiology, the nanowires enabled the bacteria that has electrically conductive pili, to

be considered as one of the most important discoveries. The microbial nanowires can be

defined as extracellular proteins that transfer an electron from cell to extracellular sub­

stances under physiological conditions [24,25].

FIGURE 11.2

Schematic illustrations of the different functions of type IV pili. Reprinted with permission [ 19]. Copyright ©

2020 Published by Elsevier, under a Creative Commons Attribution 4.0 International License (CC BY-NC-ND).

Microbial Nanowires

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