Impact of pipe material and chlorination on the biofilm structure and microbial communities

Pipe material and residual chlorine are key factors for the drinking water distribution system, and understanding the biofilm ecosystem is vital for water quality safeguard. The aim of our study was to determine the influence of pipe materials (ductile iron, steel, polyethylene) and chlorination on the biofilm structure and microbial community, as shown by the physicochemical properties, extracellular polymeric substances (EPS) structural characteristics, bacterial community composition, and functional traits. EPS spatial properties were studied based on a semi-quantitative confocal laser scanning microscope (CLSM) description. Regarding the impact of chlorination, residule chlorine (1.0 ± 0.3 mg L^-1 free chlorine) could inhibit the bacteria colonization, and initiate a potential response to external disinfectants revealed by the EPS spatial distribution changes and communities variation compared to unchlorinated system. Regarding the impact of pipe material, polyethylene (PE) biofilms displayed lower biomass, loose zoogloea structure, lower proteins and polysaccharides content, and poor microbial diversity in contrast to ductile iron and steel biofilms. Pipe material was the more possible driving factor of the biofilm community composition compared to the chlorination based on principal coordinates analysis (PCoA) and permutational multivariate analysis of variance (PERMANOVA). Actinobacteria was dominant in the PE biofilms (45.57%-83.32%), while Alphaproteobacteria (34.30%-73.22%) and Gammaproteobacteria (6.46%-36.82%) were the major classes in the steel and ductile iron biofilms. The genus Rhodococcus was predominant in the PE biofilms. Rhodococcus, Pseudomonas, and Sphingomonas seemed to have a better growth advantage in the chlorinated system and display a stronger disinfectant resistance. Functional sketch prediction indicated the potential impact of pipe material and chlorination on functional pathway abundnce, possible functional pathways associated with infectious disease included. This study provides insights into the impact of pipe material and chlorination on biofilm structure and microbial community and might help to develop monitoring or maintenance strategies to protect the biosafety of the drinking water.