Composition of the saprophytic bacterial communities in freshwater systems contaminated by heavy metals.

The bacterial communities of three aquatic systems were analyzed in order to compare the influence of heavy metals. The first system was a sedimentation pond in a zinc-copper factory. The second was the bank of the Belgian river Meuse covered by the mossPlatyhypnidium riparioides (Hedw.) Dix. contaminated with heavy metals. The third was the bank of the same river covered by the same uncontaminated moss.The study was focused mainly on cadmium.The reciprocal averaging method showed that some bacterial strains could develop in very high concentrations of cadmium, but their physiological characteristics were not the same as those of the sensitive strains. In addition, the characteristics of the resistant strains depended on the environment. Correlation between resistance to heavy metals and to antibiotics was observed but was not the same in all communities. The density of resistant strains was roughly related to the level of toxicity in the environment.