Bacterial community tolerance to Cu in soils with geochemical baseline concentrations (GBCs) of heavy metals: importance for Pollution Induced Community Tolerance (PICT) determinations using the leucine incorporation method.

Abstract PICT (Pollution Induced Community Tolerance) to Cu is a useful and sensitive tool to assess the effects of Cu pollution in soils under laboratory conditions. However, in field situations, the absence of reference values, i.e. bacterial community tolerance to Cu baseline from non-polluted soils, make the method uncertain when we want to know if a soil is or is not polluted from a microbiological point of view. In order to shed some light on this topic, the PICT (Pollution Induced Community Tolerance) concept was used to determine the bacterial community tolerance to Cu in uncontaminated soils developed on five different parent materials, using log IC50 as a tolerance index. IC50 was calculated as the amount of Cu that inhibit 50% of bacterial growth (estimated via the leucine incorporation method) in a bacterial suspension extracted from soil. With physico-chemical soil characteristics and type of parent material, a linear multiple regression equation was fitted explaining 80% of the variance in log IC50 values. This equation provides a useful tool to estimate the bacterial community tolerance to Cu baseline in a soil using the general soil characteristics, allowing for the more general use of PICT without the need of reference soils.