This study provides valuable insights into the growth potential and source contribution of NTM community along water transportation in choloramineted secondary water supply systems SWSSs.. Growth Potential and Community Dynamics of Non-Tuberculous Mycobacteria in Chloraminated Secondary Water Supply Systems

Nontuberculous mycobacteria (NTM) in drinking water distribution systems (DWDSs) pose significant health risks to humans. Secondary water supply systems (SWSSs) are particularly vulnerable to NTM proliferation due to disinfectant decay and microbial regrowth caused by prolonged water stagnation. However, the growth potential and species-level dynamics of NTM within SWSSs remain elusive. In this study, high-throughput sequencing and microbial source tracking were employed to investigate the species-level NTM community dynamics along the water transportation in chloraminated SWSSs. The gene copy number of NTM in distribution mains were approximately 3-log lower than in SWSSs, highlighting the high growth potential of NTM in SWSSs. Moreover, the significantly higher Shannon indices observed in SWSSs than distribution mains, along with the distinct separation of NTM communities between these two systems, demonstrated greater diversity of NTM community diversity within SWSSs. Additionally, clear distinctions in NTM communities across water, sediment and biofilm samples suggested the critical role of ecological niches in shaping NTM communities. The FEAST source-tracking revealed that NTM communities in household tap water mainly originated from the regrowth within SWSSs, rather from direct entry through the distribution mains. This finding underscored the critical role of SWSSs in contributing to NTM levels in household tap water. Distinguished NTM community between ceramic tank and polyethylene (PE) tank biofilm, coupled with higher Shannon indices in ceramic tank biofilm demonstrated the shaping effect of tank material on NTM communities. Furthermore, NTM community assemblage was dominated by stochastic processes along water transportation and across different ecological niches. These findings form a crucial basis for developing targeted risk mitigation strategies to control NTM proliferation in SWSSs and improve the safety of household tap water.