Type IV pili of Acidithiobacillus ferrooxidans can transfer electrons from extracellular electron donors

Abstract

Studies on Acidithiobacillus ferrooxidans accepting electrons from Fe(II) have previously focused on cytochrome c. However, we have discovered that, besides cytochrome c, type IV pili (Tfp) can transfer electrons. Here, we report conduction by Tfp of A. ferrooxidans analyzed with a conducting-probe atomic force microscope (AFM). The results indicate that the Tfp of A. ferrooxidans are highly conductive. The genome sequence of A. ferrooxidans ATCC 23270 contains two genes, pilV and pilW, which code for pilin domain proteins with the conserved amino acids characteristic of Tfp. Multiple alignment analysis of the PilV and PilW (pilin) proteins indicated that pilV is the adhesin gene while pilW codes for the major protein element of Tfp. The likely function of Tfp is to complete the circuit between the cell surface and Fe(II) oxides. These results indicate that Tfp of A. ferrooxidans might serve as biological nanowires transferring electrons from the surface of Fe(II) oxides to the cell surface.

The electrically conductive pili of Geobacter species are a recently evolved feature for extracellular electron transfer

“…Other examples of electrically conductive filaments putatively involved in extracellular electron exchange are being increasingly documented (Castro et al, 2014;Eaktasang et al, 2016;Li & Li, 2014). Further evaluation of the mechanisms for extracellular electron transfer in these organisms is also warranted.…”

Microbial nanowires: an electrifying tale

“…MNWs not only were observed in Fe-and SO 4 2À -reducing bacteria as discussed above but also were identified in the Feoxidizing bacterium Acidithiobacillus ferrooxidans (Li & Li, 2014;Valdes et al, 2008). With this discovery, it was hypothesized that MNWs may connect cells to extracellular electron donors and acceptors.…”

“…2 and relevant description is given in Table 1. Different modes of AFM including conductive AFM, scanning tunneling microscopy (STM), electrostatic force microscopy and specially designed nanofabricated electrodes are established techniques for identification and electrical characterization of MNWs produced by different micro-organisms and use of these multiple techniques has been advocated to unambiguously confirm the presence of MNWs in micro-organisms Gorby et al, 2006;Li & Li, 2014;Reguera et al, 2005;Sure et al, 2015;Venkidusamy et al, 2015;Wanger et al, 2013).…”

“…ferrooxidans and Synechocystis sp. have been found to be type IV pili (TFP) which are the most widespread type of pili present among bacteria (Li & Li, 2014;Pelicic, 2008;Reguera et al, 2005;Sure et al, 2015). Apart from common functions like adhesion and biofilm formation exhibited by most other bacterial pili, TFP possess unique functional characteristics which include twitching motility, uptake of DNA in transformation and phage attachment (Pelicic, 2008;Proft & Baker, 2009).…”

“…MNWs in Aci. ferrooxidans may be made up of PilV and PilW proteins (Li & Li, 2014). The MNWs from different micro-organisms will not always look the same and vary in width and length due to two reasons: (1) TFP have bundle forming ability as a result of which their observed width may vary; (2) length may depend on age of culture and sample preparation methods which may lead to breakage of long, delicate pili.…”