Involvement of cross-genus phages in bacterial resistance to chlorine disinfection.
Chlorine disinfection resistance in pathogenic microorganisms poses severe environmental concerns and public health risks. While phages play critical roles in host adaptation to environmental stress, how poly-host phages contribute to bacterial resistance to chlorine disinfectants remains poorly understood. Here, we investigated shifts in the population dynamics, transcriptional profiles, and function potentials of cross-genus phage-bacterial communities under exposure to chlorine disinfectants in a continuously operated anaerobic-anoxic-oxic system over a 92-day period, using integrated metagenomic and metatranscriptomic approaches. In the presence and absence of chlorine disinfectants, the genomic abundance and diversity of phage and bacterial communities showed similar variation trends, and the community structures of both exhibited clear differences. A strong significant positive correlation was observed between phage and bacterial diversity under chlorine exposure (R = 0.975, p = 0.00,057), whereas no significant correlation was detected in the absence of chlorine disinfection (R = -0.314, p = 0.613), suggesting that chlorine disinfectants may enhance phage-bacteria interactions. Host-associated phages exhibited high consistency with their corresponding putative hosts in terms of genomic abundance (M2 = 0.0945, p = 0.001) and transcript abundance (M2 = 0.3668, p = 0.001), and they were also significantly correlated with cross-genus phages in both genomic abundance (R = 0.97, p < 2.2e-16) and transcript abundance (R = 0.83, p < 2.2e-16), which collectively suggests the critical role of cross-genus phages in the resistance of microbial communities to chlorine disinfectants. Bipartite association network analysis shows that cross-genus phages carry highly homologous genes to their putative hosts and may be involved in the horizontal transfer of these genes among bacteria. These homologous genes are involved in DNA repair, redox balance regulation, environmental stress adaptation and efflux pump functions, suggesting a synergistic role between cross-genus phages and their putative hosts in chlorine resistance. Our findings reveal that cross-genus phages can contribute to the resistance of bacterial communities to chlorine disinfectants, providing the theoretical foundation for evaluating the role of poly-host phages in microbial communities.