Characterization and evolution of natural aquatic biofilm communities exposed in vitro to herbicides.

River biofilms are assemblies of autotrophic and heterotrophic microorganisms that can be affected by pollutants such as those found in watersheds and wastewater treatment plants. In the laboratory, experimental biofilms were formed from river water, and their overall composition was investigated. Denaturing gradient gel electrophoresis (DGGE) and cytometry were used to assess the richness and diversity of these communities. The software Cytostack (available on request) was developed to treat and analyze the cytometric data. Measurements of chlorophyll-a and carotenoids were used to assess the global composition of the photoautotrophic community, whereas proteins, polysaccharides (PS) content, and esterase activities were used to assess overall changes in the mixed communities. We evaluated the effects that 3 weeks of treatment with the herbicides diuron and glyphosate (10 μg L(-1)) had on these biofilms. Exposed to diuron, bacterial communities adapted, changing their composition. Glyphosate inhibited growth of one autotrophic community but caused no chlorophyll deficit. As a whole, the biofilm acted as a micro-ecosystem, able to regulate and maintain a constant level of photosynthetic pigment through the structural adaptation of the autotrophic community. These results are one more proof that microbial diversity of aquatic biofilms is influenced by chemical stresses, potentially leading to disturbances within the ecosystems.