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Applied and Environmental Microbiology, July 2003, p. 4192-4199, Vol. 69, No. 7
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.7.4192-4199.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Saprotrophic and Mycoparasitic Components of Aggressiveness of Trichoderma harzianum Groups toward the Commercial Mushroom Agaricus bisporus

Josie Williams,1 John M. Clarkson,1,{dagger} Peter R. Mills,2 and Richard M. Cooper1*

Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY,1 Department of Microbial Biotechnology, Horticultural Research International, Wellesbourne, Warwick CV35 9EF, United Kingdom2

Received 1 November 2002/ Accepted 16 April 2003

We examined the mycoparasitic and saprotrophic behavior of isolates representing groups of Trichoderma harzianum to establish a mechanism for the aggressiveness towards Agaricus bisporus in infested commercial compost. Mycoparasitic structures were infrequently observed in interaction zones on various media, including compost, with cryoscanning electron microscopy. T. harzianum grows prolifically in compost in the absence or presence of A. bisporus, and the aggressive European (Th2) and North American (Th4) isolates produced significantly higher biomasses (6.8- and 7.5-fold, respectively) in compost than did nonaggressive, group 1 isolates. All groups secreted depolymerases that could attack the cell walls of A. bisporus and of wheat straw, and some were linked to aggressiveness. Growth on mushroom cell walls in vitro resulted in rapid production of chymoelastase and trypsin-like proteases by only the Th2 and Th4 isolates. These isolates also produced a dominant protease isoform (pI 6.22) and additional chitinase isoforms. On wheat straw, Th4 produced distinct isoforms of cellulase and laminarinase, but there was no consistent association between levels or isoforms of depolymerases and aggressiveness. Th3's distinctive profiles confirmed its reclassification as Trichoderma atroviride. Proteases and glycanases were detected for the first time in sterilized compost colonized by T. harzianum. Xylanase dominated, and some isoforms were unique to compost, as were some laminarinases. We hypothesize that aggressiveness results from competition, antagonism, or parasitism but only as a component of, or following, extensive saprotrophic growth involving degradation of wheat straw cell walls.

* Corresponding author. Mailing address: Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom. Phone: 44 0 1225 383051. Fax: 44 0 1225 826779. E-mail: bssrmc{at}bath.ac.uk.

{dagger} Present address: Molecular Sensing plc, Melksham, Wiltshire SN12 8LH, United Kingdom.

Applied and Environmental Microbiology, July 2003, p. 4192-4199, Vol. 69, No. 7
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.7.4192-4199.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.





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