As disinfection strategies could support a shift of some bacterial populations, the biodiversity of drinking water biofilms depending on the disinfectant concentrations was explored. The effect of different chlorine sequences applied for several weeks (0.1-0.4-0.1 mg Cl(2)L(-1) or vice versa) was tested on the abundance of the alpha-, beta- and gamma-proteobacteria populations, used as indicators of changes in bacterial populations within drinking water biofilms. Using dynamic (industrial pilot) and batch (bench scale) conditions, our work demonstrated the ability of the 3 proteobacteria subclasses to re-organize following discontinuous chlorinations. The beta- and gamma-proteobacteria subclasses were favoured by high free residual chlorine concentrations (0.4 mg Cl(2)L(-1)) while alpha-proteobacteria population was sensitive to this oxidant level. The proteobacteria population shifts within the biofilm exposed to discontinuous chlorination were reversible. The resilience of the biofilm proteobacteria populations exposed to oxidant stress questioned the emergence of bacterial population less sensitive to chlorine.