Electrochemical communication between microbial cells and electrodes via osmium redox systems

Abstract

Electrochemical communication between micro-organisms and electrodes is the integral and fundamental part of BESs (bioelectrochemical systems). The immobilization of bacterial cells on the electrode and ensuring efficient electron transfer to the electrode via a mediator are decisive features of mediated electrochemical biosensors. Notably, mediator-based systems are essential to extract electrons from the non-exoelectrogens, a major group of microbes in Nature. The advantage of using polymeric mediators over diffusible mediators led to the design of osmium redox polymers. Their successful use in enzyme-based biosensors and BFCs (biofuel cells) paved the way for exploring their use in microbial BESs. The present mini-review focuses on osmium-bound redox systems used to date in microbial BESs and their role in shuttling electrons from viable microbial cells to electrodes.

Direct electrochemistry and Os-polymer-mediated bioelectrocatalysis of NADH oxidation by Escherichia coli flavohemoglobin at graphiteelectrodes

“…This wiring approach was previously used to achieve bioelectrocatalysis of such FAD containing enzymes as glucose oxidase (Gregg and Heller, 1990;Mao et al, 2003), diaphorase (Antiochia and Gorton, 2007;Tasca et al, 2008;Tsujimura et al, 2002a), pyranose oxidase (Timur et al, 2006;Zafar et al, 2010), FAD-dependent glucose dehydrogenase (Zafar et al, 2012) and in the development of O 2 -reducing biocathodes based on blue-copper enzymes such as laccases (Barriere et al, 2004;Daigle et al, 1998) and bilirubin oxidase (Mano et al, 2002;Tsujimura et al, 2002b). It was also successfully used for wiring of the redox centers of such a fragile membrane enzyme complex as theophylline oxidase (Shipovskov and Ferapontova, 2008), providing retention of its bioelectrocatalytic activity within the polymer matrix (Ferapontova et al , 2006), and even those of whole cells (Coman et al, 2009;Hasan et al, 2012;Vostiar et al, 2004).…”

Photoelectrochemical Wiring of Paulschulzia pseudovolvox (Algae) to Osmium Polymer Modified Electrodes for Harnessing Solar Energy

“…This would mean that the electron exit via the photosynthetic redox complexes (PRCs) of prokaryotic cyanobacteria should in principle be comparatively easier than those of their eukaryotic counterparts. Os-polymers supply the systems including bacterial cells, [17][18][19] with high concentrations of stable mediating functionalities; form a 3D hydrogel [ 20 ] containing multiple layers of enzymes/ cells, [ 21 ] in which substrates and products can easily diffuse in and out. However, the inevitability of regular and continuous addition of these mediators makes them technologically unfeasible, environmentally unfriendly, practically incompatible [ 6 ] and maybe harmful for cells.…”

The ins and outs of microorganism–electrode electron transfer reactions

“…This observation may partially account for the enhancement of electrocatalytic biofilm performance observed on hydrophilic surfaces and highlights the potential mechanistic insights that may be gained from such studies. In addition to modifying electrode surfaces, use of redox and/or conducting polymers [90][91] and/or nanomaterials could also be explored to electrically wire microorganisms to electrodes, including connecting metabolic processes inside cells to electrodes outside cells in a manner analogous to that used to wire redox enzymes to electrode surfaces [92][93] . This is an under-exploited approach to engineering microbial BES which may expand the scope of useable microorganisms to those with interesting/useful catalytic properties but that lack ability to electrically wire themselves to electrodes [94][95] .…”