INFLUENCE OF DIFFERENT TEMPERATURES ON METAL TOLERANCE MEASUREMENTS AND GROWTH-RESPONSE IN BACTERIAL COMMUNITIES FROM UNPOLLUTED AND POLLUTED SOILS

The effects of temperature on the growth rate and metal toxicity in so il bacterial communities extracted from unpolluted and polluted soils were investigated using the thymidine and leucine incorporation techni ques. An agricultural soil, which was contaminated in the laboratory w ith Cu, Cd, Zn, Ni or Pb, and an uncontaminated forest soil were used. Measurements were made at 0 degrees C and 20 degrees C. Leucine incor poration was found to be as sensitive to heavy metals as thymidine inc orporation in the short-term trial used to indicate heavy metal tolera nce. Similar IC50 values (the log of the metal concentration that redu ced incorporation to 50%) were also obtained at 0 and 20 degrees C, in dependently of the technique used. Metal tolerance could thus be measu red using both techniques at any temperature in the range 0-20 degrees C. In the long-term experiment different temperature-growth relations hips were obtained on the basis of the rate of thymidine or leucine in corporation into bacterial assemblages from unpolluted and polluted so ils, as judged from the minimum temperature values. This could not be attributed to the metal addition alone since different patterns were o bserved when different metals were added to the soil. Thus, the minimu m temperature for thymidine incorporation was similar in Cu-polluted a nd unpolluted soil, while in soils polluted with Cd and Zn the minimum temperature increased by 2 degrees C, and Ni and Pb additions increas ed the minimum temperature by 4 degrees C compared to the unpolluted s oil. This suggested that heavy metal pollution led to bacterial commun ities showing different temperature characteristics to those in the co rresponding unpolluted soil. Similar observations were deduced from th e minimum temperatures required for leucine incorporation. Three group s of bacterial communities were distinguished according to the growth response to temperature in polluted soils, one group in Cu-polluted so il, a second group in soil polluted with Zn and Cd, and a third group in soils polluted with Ni and Pb.