Implementation and comparison of two concentration methods to detect and characterize bacteriophages and bacterial hosts from large drinking water samples.

Drinking water distribution systems (DWDS) are low biomass biomes harboring a large variety of microorganisms. Much of the attention has been focused on bacteria, whose diversity and abundance in DWDS were repeatedly shown to be influenced by abiotic factors such as pH, temperature, growth inhibitors and water sources. However, little is known about biotic factors, such as bacteriophage presence, even though they are known to be present in DWDS and to influence bacterial dynamics. While bacteriophage impact has been assessed in natural environments such as oceans, little is known about the way they shape DWDS bacterial communities. To fill this knowledge gap and accessing bacteriophage diversity from such low biomass environment, the present study aimed to propose and compare two methods based on ultrafiltration and adsorption/elution methods, already used for the concentration of bacteria and virus from water. To this end, both methods were compared with a weekly sample collection, for one month, on the DWDS of Paris, France. Metagenomic sequencing was performed on concentrated samples to investigate the presence and diversity of bacteriophages, using a coupling of complementary bioinformatic prediction tools. Though viral fractions represented a minority of recovered contigs (1.5 to 2.5%), most were associated with Caudoviricetes class. The predicted bacterial hosts matched with the observed bacterial diversity, highlighting the robustness of host prediction tool. A total of 437 putative phages were present in all samples, constituting a core phage diversity. Among those, 380 viral contigs contained sequences showing significant non-viral matches. We leveraged this information to further refine the inference of bioinformatics pairs of bacterial hosts and their phages. In conclusion, we propose a method to simultaneously concentrate bacteriophages with bacteria from low-biomass environment. Through metagenomics, this study showed that an optimized bioinformatic pipeline could provide an overview of DWDS phage diversity. Moreover, this method allowed to detect sequence similarities between phages and bacteria, suggesting potential genetic exchanges and providing clues for host spectrum. Altogether, this study highlights the tight interactions between bacteria and bacteriophages in drinking water and the possibility to study both phages and potential hosts to better grasp their intricate interplay.