Bacterial evolution in biofiltration of drinking water treatment plant: different response of phage and plasmid to varied water sources

Biofiltration in drinking water treatment (BDWT) are popular as it holds promise as an alternative to chemical treatments, yet our understanding of the key drivers and trends underlying bacterial evolution within this process remains limited. While plasmids and phages are recognized as the main vectors of horizontal gene transfer (HGT), their roles in shaping bacterial evolution in BDWT remain largely unknown. Here we leverage global metagenomic data to unravel the primary forces driving bacterial evolution in BDWT. Our results revealed that the primary vector of HGT varies depending on the type of source water (groundwater and surface water). Both plasmids and phages accelerated bacterial evolution in BDWT by enhancing genetic diversity within species, but they drove contrasting evolutionary trends in functional redundancy in different source water types. Specifically, trends towards and away from functional redundancy (indicated as gene-protein ratio) were observed in surface-water and groundwater biofilters, respectively. Virulent phages drove bacterial evolution through synergistic interactions with bacterial species capable of natural transformation and with certain natural compounds that disrupt bacterial cytoplasmic membranes. Genes relating to water purification (such as Mn(II)-oxidizing genes), microbial risks (antibiotic resistance genes), and chemical risk (polycyclic aromatic hydrocarbons) were enriched via HGT in BDWT, highlighting the necessity for heighted focus on these useful and risky objects. Overall, these discoveries enhance our understanding of bacterial evolution in BDWT and have implications for the optimization of water treatment strategies.