Changes in activity of extracellular enzymes in dual cultures of Lentinula edodes and mycoparasitic Trichoderma strains N. Hatvani 1 , L. Kredics 2 , Z. Antal 2 and I. Me ´cs 1 1 Zoltan Bay Foundation for Applied Research, Institute for Biotechnology, Szeged, and 2 Hungarian Academy of Sciences and University of Szeged, Microbiological Research Group, Szeged, Hungary 72/01: received 23 April 2001, revised 13 September 2001 and accepted 13 September 2001 N. HATVANI, L. KREDICS, Z. ANTAL AND I. ME ´ C S . 2002. Aims: The main problem that arises during the cultivation of Lentinula edodes, the Asian Shiitake mushroom, is that the logs on which the cultivation is performed are contaminated by competing micro-organisms, especially Trichoderma spp. The aim of this study was to examine the changes in activity of extracellular enzymes in dual cultures of Trichoderma spp. and L. edodes. Methods and Results: Extracellular enzyme activities were determined spectrophotometri- cally. Trichoderma enzymes important for the degradation of fungal cell walls (N-acetyl-b- glucosaminidase and laminarinase) were shown to be induced by inactive L. edodes mycelia in liquid culture. The changes that occurred in the extracellular enzyme activities of L. edodes and mycoparasitic Trichoderma spp. (T. aureoviride, T. harzianum and T. viride) were examined during antagonistic interactions on solid medium. The extracellular enzyme patterns of both partners proved to be altered. Trichoderma spp. were induced to produce N-acetyl-b- glucosaminidase and laminarinase in the presence of active L. edodes mycelia, similarly as observed in liquid culture. The activities of both laccase and manganese peroxidase of L. edodes decreased after physical contact with active Trichoderma mycelia, possibly in consequence of the beginning of degradation of L. edodes by the Trichoderma enzymes. However, besides a decrease in manganese peroxidase activity, an enhancement of L. edodes laccase activity was observed on solid media containing crude culture fluids from Trichoderma liquid cultures. The metabolites responsible for these effects proved to be heat stable. Conclusions: Induction and inhibition of several extracellular enzymes of both partners were shown in dual cultures of L. edodes and Trichoderma strains, indicating the important role of these enzymes in the antagonistic interaction between the two species. Significance and Impact of the Study: As the main problem during the large-scale cultivation of L. edodes is the contamination of the growth substrate by Trichoderma mycelia, the particular knowledge of the mechanism of this competition might be relevant. INTRODUCTION Lentinula edodes, the Asian Shiitake mushroom, is the second most popular edible mushroom worldwide. This white rotting fungus is cultivated on artificial logs made of various sterilized lignocellulosic substrates. The main problem during its cultivation is the contamination of the logs by competing fungi (Royse et al. 1985). Lentinula edodes produces several compounds that exert inhibitory effects on a wide range of microbes (Jong and Birmingham 1993; Hatvani 2001), and such compounds may play a role in the defence against competitors. The group of competing fungi causing the greatest losses are species belonging in the genus Trichoderma (Badham 1991; Tokimoto and Komatsu 1979). Trichoderma spp. exert Correspondence to: Nora Hatvani, Zoltan Bay Foundation for Applied Research, Institute for Biotechnology, PO Box 2337, H-6701 Szeged, Hungary (e-mail: hnora@bay.u-szeged.hu). ª 2002 The Society for Applied Microbiology Journal of Applied Microbiology 2002, 92, 415–423