Electron transfer between genetically modified Hansenula polymorpha yeast cells and electrode surfaces via Os-complex modified redox polymers.

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.