We investigated the effects of copper on the structure and physiology of freshwater biofilm microbial communities. For this purpose, biofilms that were grown during 4 weeks in a shallow, slightly polluted ditch were exposed, in aquaria in our laboratory, to a range of copper concentrations (0, 1, 3, and 10 M). Denaturing gradient gel electrophoresis (DGGE) revealed changes in the bacterial community in all aquaria. The extent of change was related to the concentration of copper applied, indicating that copper directly or indirectly caused the effects. Concomitantly with these changes in structure, changes in the metabolic potential of the heterotrophic bacterial community were apparent from changes in substrate use profiles as assessed on Biolog plates. The structure of the phototrophic community also changed during the experiment, as observed by microscopic analysis in combination with DGGE analysis of eukaryotic microorganisms and cyanobacteria. However, the extent of community change, as observed by DGGE, was not significantly greater in the copper treatments than in the control. Yet microscopic analysis showed a development toward a greater proportion of cyanobacteria in the treatments with the highest copper concentrations. Furthermore, copper did affect the physiology of the phototrophic community, as evidenced by the fact that a decrease in photosynthetic capacity was detected in the treatment with the highest copper concentration. Therefore, we conclude that copper affected the physiology of the biofilm and had an effect on the structure of the communities composing this biofilm.Copper has been applied as an algaecide for many years, e.g., in antifouling ship paints, and has been used in the composition of many materials, such as porcelains and bricks, which for a long time were simply deposited in dumping grounds when no longer in use, increasing the load of cupric compounds in soils and waters, and leading to concerns about their toxicity. However, our knowledge of the effects of this metal on the structure and function of microbial communities in freshwater is still limited. Several detrimental effects of Cu have been reported to occur in pure cultures of phototrophic species. These effects include depression of photosynthesis and respiration, inhibition of cell division, and cell death (15). Aquatic microorganisms, phytoplankton and bacteria, often live in communities, forming organized assemblages at the surfaces of rocks, sediment, and submerged plants. These epilithic, epiphytic, or epipelon assemblages are generally described as biofilms (30). Barranguet et al., studying heavy metal effects on aquatic biofilms, showed that Cu affects the physiology of phototrophic organisms (1), that it accumulates in phototrophic biofilms proportionally to the concentration of exposure, and that some algal species react morphologically to an increased Cu concentration (3). However, the measured Cu effects on the photosystem were not related to changes occurring in the composition of the phototrophic community as...
