Graduate Thesis Or Dissertation
 

Measuring extracellular enzymes in pure and mixed cultures of Trametes versicolor (L.:Fr.) Pilat and Trichoderma harzianum Rifai

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  • The biocontrol potential of Trichoderma harzianum Rifai, Trichoderma polysporum (Link.:Pers.) Rifai, Scytalidium aurantiacum Klingstr. et Beyer or a Penicillium sp. against Trametes versicolor (L. :Fr.) Pilat, Neolentinus lepideus (Fr.) Redh. et Ginns, Postia placenta (Fr.) M.Lars. et Lomb. and Irpex lacteus Fr. was evaluated using agar plate, soil bottle and small size wood wafer tests. Although T. harzianum arrested growth of several wood decay fungi, it never killed them on wood samples. Of the tested microfungi, S. aurantiacum performed best in the wood-based assays. At the same time, the utility of small size wood assays for evaluation of biocontrol potential was demonstrated. Such assays are more rapid and versatile than full-scale soil bottle or sawdust tube tests, and provide more information than agar plate screenings. Microscopic examination of hyphal interactions between T. versicolor and T. harzianum on microscope slide cultures yielded little additional information, partly due to the experimental system chosen. No hyphal interference or lysis of cell walls was observed, possibly due to the high nutrient levels in the slide cultures. The activities of enzymes related to wood decay were studied in pure and mixed liquid cultures of T. versicolor and T. harzianum at low (0.4 mM) and high (4 mM) nitrogen concentrations. In high nitrogen medium, total filter paper cellulase, specific and total cellobiase, and specific and total laccase increased when compared to activities obtained in low nitrogen concentrations. Conversely, specific filter paper cellulase and peroxidase activities were enhanced under nitrogen limiting conditions. Influences of T. harzianum on extracellular enzyme production of T. versicolor were observed. Total and specific laccase activities were induced in media containing both low and high nitrogen levels, whilst filter paper cellulase activities decreased. Peroxidase and cellobiase activities remained at approximately the same level or were decreased in mixed cultures. The experimental system chosen allowed no separation of mycelia or culture liquids of the two fungi incubated in mixed culture. Therefore, few conclusions with respect to induction, inhibition or regulation of the monitored enzymes could be reached. None of the enzyme activities was correlated with biomass production. Laccases and Poly R-478 peroxidase activity indicated survival of the T. versicolor, since T. harzianum did not produce these two enzymes.
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