Using planktonic microorganisms to supply the unpurified multi-copper oxidases laccase and copper efflux oxidases at a biofuel cell cathode
Résumé
The feasibility to apply crude culture supernatants that contain the multicopper oxidases laccase or copper efflux oxidase (CueO) as oxygen reducing catalysts in a biofuel cell cathode is shown. As enzyme-secreting recombinant planktonic microorganisms, the yeast Yarrowia lipolytica and the bacterium Escherichia coli were investigated. The cultivation and operation conditions (choice of medium, pH) had distinct effects on the electro-catalytic performance. The highest current density of 119 +/- 23 mu A cm(-2) at 0.400 V vs. NHE was obtained with the crude culture supernatant of E. coli cells overexpressing CueO and tested at pH 5.0. In comparison, at pH 7.4 the electrode potential at 100 mu A cm(-2) is 0.25 V lower. Laccase-containing supernatants of Y. lipolytica yielded a maximum current density of 6.7 +/- 0.4 mu A cm(-2) at 0.644 V vs. NHE. These results open future possibilities to circumvent elaborate enzyme purification procedures and realize cost effective and easy-to-operate enzymatic biofuel cells.