The aim of this study is to investigate the adaptation of tolerance levels of biofilms transplanted either from a non-contaminated area to an urban-contaminated site or, conversely, from a contaminated area to a non-impacted site. For that purpose, natural fluvial biofilms were collected upstream the urban area of Paris (site A) and transplanted downstream from Paris (site B2), and conversely, biofilms were collected in the urban area of Paris (site B1) and transplanted upstream (site A). Cu tolerance levels of biofilms (both transplanted and original communities) were measured, using a previously developed short-term toxicity test based on the measure of beta-glucosidase activity, just before transplantation and then 15 and 30 days later. Automated-Ribosomal Intergenic Spacer Analysis (ARISA) was used to analyze similarities in both bacterial and eukaryotic community structures of the biofilms.