Laccases are multicopper oxidoreductases with broad substrate specificity and are applied in biofuel cells at the cathode to improve its oxygen reduction performance. However, the production of laccases by e.g. fungi is often accompanied by the need of synthetic growth supplements for increased enzyme production. In this study we present a strategy for the white-rot fungus Pleurotus sajor-caju for natural laccase activity induction using lignocellulose substrates and culture supernatant of Aspergillus nidulans. P. sajorcaju laccases were secreted into the supernatant, which was directly used at a carbon-nanotube bucky-paper cathode in a biofuel cell. Maximal current densities of -148 +/- 3 mu A cm(-2) and -102 +/- 9 mu A cm(-2) at 400 mV were achieved at pH 5 and 7, respectively. Variations in cathode performance were observed with culture supernatants produced under different conditions due to the induction of specific laccases. (C) 2016 Elsevier Ltd. All rights reserved.