Soluble Iron Enhances Extracellular Electron Uptake by Shewanella oneidensis MR‐1

Abstract

Extracellular electron transfer (EET) is a process that microorganisms use to reduce or oxidize external insoluble electron acceptors or donors. Much of our mechanistic understanding of this process is derived from studies of transmembrane cytochrome complexes and extracellular redox shuttles that mediate outward EET to anodes and external electron acceptors. In contrast, there are knowledge gaps concerning the reverse process of inward EET from external electron donors to cells. Here, we describe a role for soluble iron (exogenous FeCl2) in enhancing EET from cathodes to the model EET bacterium Shewanella oneidensis MR‐1, with fumarate serving as the intracellular electron acceptor. This iron concentration‐dependent electron uptake was eradicated upon addition of an iron chelator and occurred only in the presence of fumarate reductase, confirming an electron pathway from cathodes to this periplasmic enzyme. Moreover, S. oneidensis mutants lacking specific outer membrane and periplasmic cytochromes exhibited significantly decreased current levels relative to wild‐type. These results indicate that soluble iron can function as an electron carrier to the EET machinery of S. oneidensis.

Research progress on using biological cathodes in microbial fuel cells for the treatment of wastewater containing heavy metals

“…For example, owing to its small dissociation constant, Shewanella oneidensis MR-1 uses autocrine riboflavin, which readily acts as an electron mediator to transfer electrons to Cr(VI) and remove them via reduction ( Pang et al, 2013 ). Recently, the exogenous presence of Fe(II) significantly increased the ability of MR-1 to accept electrons from the cathode ( Abuyen and El-Naggar, 2023 ). These mediators can significantly reduce the internal resistance to charge transfer and internal diffusion resistance of the cathode, increasing the electron-transfer rate.…”

“…Recently, the exogenous presence of Fe(II) significantly increased the ability of MR-1 to accept electrons from the cathode (Abuyen and El-Naggar, 2023). These mediators can significantly reduce the internal resistance to charge transfer and internal diffusion resistance of the cathode, increasing the electron-transfer rate.…”

Insights into the various mechanisms by which Shewanella spp. induce and inhibit steel corrosion

“…Nevertheless, flavins secreted by S. loihica were already found to catalyze cathodic O 2 reduction 38 . Recently, soluble Fe(II) was also found to play a role as electron shuttle in the cathodic electron uptake by S. oneidensis MR1 39 .…”

Engineering bionanoreactor in bacteria for efficient hydrogen production

“…Considerable efforts have been devoted to enhancing the extracellular electron-transfer processes ( 18 , 19 ). Introducing electron-shuttling molecules such as flavins ( 20 ) and iron ions ( 21 ) has been widely used to boost the electrochemical performance of S. oneidensis MR-1. Recent strategies focus on coupling the nanoparticle with S. oneidensis MR-1, which have been reported to significantly promote extracellular electron transfer ( 17 , 18 , 22 ).…”