Biofilms - drug effects, Gene Dosage - genetics, Mercury - analysis, Oxidoreductases - genetics, Bacteria - drug effects, Drug Tolerance, Phylogeny, Biodiversity, Water Pollutants, Chemical - analysis, Bacteria - genetics, Mercury - toxicity, Water Pollutants, Chemical - toxicity, Bacteria - classification, RNA, Ribosomal, 16S - genetics, Rivers - microbiolo...