Electron Transfer between Genetically Modified Hansenula polymorpha Yeast Cells and Electrode Surfaces via Os-complex modified Redox Polymers

Abstract

Graphite electrodes modified with redox-polymer-entrapped yeast cells were investigated with respect to possible electron-transfer pathways between cytosolic redox enzymes and the electrode surface. Either wild-type or genetically modified Hansenula polymorpha yeast cells over-expressing flavocytochrome b2 (FC b(2) ) were integrated into Os-complex modified electrodeposition polymers. Upon increasing the L-lactate concentration, an increase in the current was only detected in the case of the genetically modified cells. The overexpression of FC b(2) and the related amplification of the FC b(2) /L-lactate reaction cycle was found to be necessary to provide sufficient charge to the electron-exchange network in order to facilitate sufficient electrochemical coupling between the cells, via the redox polymer, to the electrode. The close contact of the Os-complex modified polymer to the cell wall appeared to be a prerequisite for electrically wiring the cytosolic FC b(2) /L-lactate redox activity and suggests the critical involvement of a plasma membrane redox system. Insights in the functioning of whole-cell-based bioelectrochemical systems have to be considered for the successful design of whole-cell biosensors or microbial biofuel cells.

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.…”

Yeast as a Biocatalyst in Microbial Fuel Cell

“…Several yeast strains have been studied as biocatalysts in MFC with or without external mediator such as Saccharomyces cerevisiae (S. cerevisiae) [41][42][43][44][45][46][47][48][49][50][51][52], Candida melibiosica 2491 (C. melibiosica) [53][54][55][56], Hansenula anomala (H. anomala) [40], Hansenula polymorpha (Hansenula polymorpha) [57], Arxula adeninivorans (A. adeninivorans) [58] and Kluyveromyces marxianus (K. marxianus) [59].…”

“…The electron transfer pathways between the cytosolic redox enzymes of H. polymorpha, overexpressing flavocytochrome b2 (FC b2), and the electrode surface was studied [57]. Both wild and genetic H. polymorpha yeast cells were entrapped in osmium-complex-modified redox polymers (OsRP), which are essential for the electron transfer communication, on the surface of graphite electrodes.…”

Electrochemical communication between microbial cells and electrodes via osmium redox systems

“…The idea of employing yeasts as a substitute to bacteria in BESs is surfacing, since they are robust and generally nonpathogenic. With regard to their capability to metabolize a wide range of substrates and high growth rates, Shkil et al [45] reported the electrochemical communication of Hansenula polymorpha with a graphite electrode, by wiring with osmium redox systems V, VI and VII. Here, genetically modified yeast cells that overexpress FCb2 (flavocytochrome b 2 ) generated more significant current with the aid of these osmium redox systems compared with that observed for the wild-type cells, highlighting that a plasma membrane redox system (FCb2) is crucial for ET.…”

“…Based on [44]. (B and C) Exemplary schemes that show electrical wiring of Gram-positive bacterial cell [43] and yeast cell [45] respectively to the electrode via osmium complexes.…”