Nitrogen deregulated manganese peroxidase (MnP)-producing mutants of Deuteromycotina IZU-154 were isolated based on their ability of decolorize synthetic melanin. One of these mutants, IZU-882, exhibited an approximately 2-fold higher level of MnP activity, 8-12 nkat/ml (nano katal/ml), under nitrogen nonlimiting conditions than that of the wild-type under nitrogen limiting conditions.