In vitro water activity and pH dependence of mycelial growth and extracellular enzyme activities of Trichoderma strains with biocontrol potential

Aims: Water activity (a(w)) and pH are probably the most important environmental parameters affecting the activities of mycoparasitic Trichoderma strains. Therefore it is important to collect information on the effects of these factors on mycelial growth and on the in vitro activities of extracellular enzymes involved in nutrient competition (e.g. beta-glucosidase, cellobiohydrolase and beta-xylosidase) and mycoparasitism (e.g. N-acetyl-beta-glucosaminidase, trypsin-like protease and chymotrypsin-like protease) of Trichoderma strains with biocontrol potential. Methods and Results: Water activity and pH dependence of the linear mycelial growth of five examined Trichoderma strains belonging to three different species groups was examined on yeast extract and soil extract media. Maximal growth rates were observed at a(w) 0.997 and pH 4.0 in the case of all strains. The activities of the examined extracellular enzymes at different a(w) and pH values were determined spectrophotometrically after incubation with chromogenic p-nitrophenyl and p-nitroaniline substrates. Maximal enzyme activities were measured at a(w) 0.950 for beta-glucosidase, trypsin-like protease and chymotrypsin-like protease, at 0.910 for cellobiohydrolase and at 0.993 for beta-xylosidase and N-acetyl-beta-glucosaminidase enzymes. Optimal pH values are suggested to be at 5.0 for beta-glucosidase, cellobiohydrolase and N-acetyl-beta-glucosaminidase, at 3.0 for beta-xylosidase, at 6.0 for trypsin-like protease and between 6.0 and 7.0 for chymotrypsin-like protease activities, respectively. Conclusions: Extracellular enzymes of the examined mycoparasitic Trichoderma strains are able to display activities under a wider range of a(w) and pH values than those allowing mycelial growth. Significance and Impact of the Study: Data about the effects of a(w) and pH on mycelial growth and extracellular enzyme activities of Trichoderma reveal useful information about the applicability of biocontrol strains in agricultural soils with specific water and pH relations.