Biofilm and planktonic bacterial communities in a drinking water distribution system supplied with untreated groundwater.

It is known that both disinfection and water quality can influence the bacterial communities in a drinking water distribution system (DWDS). Here, we hypothesized that bacterial communities in a DWDS with untreated groundwater with no prior purification and disinfection might differ from those in a DWDS with disinfected surface water. The present study applied Illumina MiSeq sequencing to investigate biofilm and planktonic bacterial communities in a DWDS fed with untreated groundwater (receiving no prior purification and disinfection). Considerable differences in bacterial richness (Chao1 richness estimator: 389-745 for water and 392-485 for biofilm), diversity (Shannon diversity index: 2.70-3.77 for water and 2.53-3.66 for biofilm) and community structure existed among both DWDS waters and biofilms. Biofilm and planktonic bacterial communities had distinct structures. The service time of DWDS could affect biofilm bacterial richness, diversity and community structure. Moreover, planktonic bacterial diversity and community structure might be influenced by NO2 - concentration, while planktonic bacterial richness was related to NO3 - concentration. Proteobacteria dominated in both biofilm and planktonic bacterial communities. Higher concentrations of NO2 - favored the deltaproteobacterial proportion, but lowered the gammaproteobacterial proportion in drinking water. Overall, our study indicates that bacterial communities in a DWDS could be influenced by a variety of factors, such as habitats (water or biofilm), DWDS service time, and water chemistry.