Microbial responses to single or successive soil contamination with Cd or Cu

The effects of either single or successive additions of Cd or Cu on colony formation, microbial activity and microbial community structure of heterotrophic bacteria in a sandy-loam soil were studied. Soil samples were treated with a single dose of either 5000 μg Cd g−1 or 5000 μg Cu g−1. Successive additions were made on the first day as 1000 μg Cd g−1 or 1000 μg Cu g−1, respectively, and thereafter, at weekly intervals, 1150, 1300, 1450 and 100 μg g−1 of the metals were added to the samples. The successive additions of Cd or Cu did not affect the numbers of heterotrophic bacteria any more than the single doses. However, differences in microbial activity and the values of parameters characterizing the process of colony formation by soil bacteria were observed. Results show that soil heterotrophic bacteria are resistant to heavy metals, which, however, change biochemical activity and physiological state. Microbial community structure was dominated by K-strategists. Single or successive additions of Cd or Cu did not affect the distribution of the classes in K-strategist communities. However, bacterial community distribution curves indicate that different populations of K-strategists evolved during experiments.