Retrospective Analysis of Drinking Water Microcosm Microbiomes Reveals an Apparent Antagonistic Relationship between Neochlamydia and Legionella

Legionella pneumophila (Lp) can sometimes establish in drinking water microbial communities and infect individuals inhaling contaminated aerosols. The premise plumbing portion of the drinking water distribution system is often especially vulnerable to Lp growth. Innovative approaches to intentionally manipulate the microbial ecology to control Lp have been proposed but remain elusive. Here, we retrospectively analyzed 16S rRNA gene amplicon sequences and droplet digital PCR data in samples derived from prior drinking water studies, wherein some inexplicable stochastic variations in the Lp occurrence were observed in replicate microcosms. We discovered an apparent antagonistic relationship between Legionella and Neochlamydia. This relationship was noted across three water sources (Flint, Detroit, and Blacksburg) and was at least partially mediated by the presence of copper, through either copper pipes or a dosed range of 0–2000 μg/L total copper. The observations of this study, which was conducted under realistic drinking water conditions harboring mixed microbial communities, are consistent with recent pure culture studies reporting that Legionella amoebic uptake may be inhibited when Neochlamydia are established as amoebal endosymbionts. The findings may help explain the apparent stochastic behavior of Lp in field and research settings and may open a door to new engineered ecological control strategies for Lp.