Nitrato reduttasi e beta-galattosidasi come indicatori d'adattamento microbico in un suolo contaminato da zinco

[Autom. eng. transl.] The enzymatic activities and in general the biological properties are extensively studied to evaluate the ecotoxicological response of soil microorganisms to the presence of contaminants. Tests conducted in the past have shown that nitrifying microorganisms are able to adapt to the presence of trace elements. The present study was conducted to assess whether other soil microorganisms are able to adapt to the presence of zinc in toxic concentrations. Microcosms contaminated with zinc (350 mg kg-1 ss) were incubated together with controls uncontaminated with zinc for a period of 4 months, and at regular intervals potential nitrification, nitrate reductase and β-galactosidase were determined. The 3 activities showed a significant reduction in the contaminated microcosms with respect to the controls immediately after the contamination, and an increase in the following samplings, until reaching statistically different values from the controls to 99 days of incubation for the potential nitrification, to 71 days for the nitrate reductase and already at 41 days for β-galactosidase. To confirm that the recovery of functionality was due to real adaptation and not to aging phenomena, both the samples contaminated with zinc and the control samples at the end of the incubation period (113 days) were reinoculated in sterilized and contaminated soils by a few hours with increasing concentrations of zinc (0-5000 mg kg-1 ss). The comparison of the dose-response curves showed significant increases in EC50 in soils inoculated with pre-exposed microcosms for all 3 activities. It was thus possible to demonstrate that not only nitrification, but also nitrate redactase and β-galactosidase are indicators of microbial adaptation to zinc contamination.