The effects of external pH, temperature, and substrate concentration on acid phosphatase activity of ectomycorrhizal fungi

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Abstract
Isolates of the ectomycorrhizal fungi Cenococcum geophilum, Hebeloma pusillum, and Entoloma sericeum were grown in axenic culture to study the effects of assay pH, temperature, and substrate concentration on the activity of surface acid phosphatases. In addition, isolates were grown at 12 and 20 °C to determine whether the Arrhenius activation energies of surface phosphatases were affected by temperature acclimation. Four of the six isolates examined demonstrated distinct pH optima at pH 5.0; one isolate showed optimal activity at pH 4.5. None of the fungi examined produced significant surface alkaline phosphatase activity. Arrhenius activation energy values were not affected by lowering the growth temperature, suggesting that a phenotypic change in surface acid phosphatases did not occur with acclimation. Vmax and Km values for the hydrolysis of p-nitrophenyl phosphate were found to differ significantly among the isolates examined. Our findings support previous research by confirming the existence of interspecific and intraspecific differences in acid phosphatase activity, but they demonstrate the importance of considering assay pH and substrate concentration when making such comparisons.