Microbial community structure and pathogen persistence in tropical drinking water distribution systems: the role of seasonality and treatment

Microbial ecosystems within drinking water distribution systems (DWDS) are shaped by environmental pressures and treatment processes, yet their eukaryotic components and interactions with bacterial communities remain underexplored, particularly in tropical island contexts. This study investigated the seasonal dynamics of microbial communities in 17 DWDS across Guadeloupe (French West Indies), encompassing both untreated (river and groundwater) and treated sources (storage tanks and tap water). Over one year, 90 samples were collected during rainy and dry seasons. Microbial diversity was assessed using high-throughput 16S and 18S rRNA gene sequencing, combined with culture-based enrichment methods. Eukaryotes were selectively enriched via incubation at 30, 37, and 44 °C with bacteria or yeast, followed by DNA extraction and 18S sequencing. Bacterial communities were analysed from both free-living fractions and from amoebae-enriched samples. The 18S results revealed distinct eukaryotic community structures across water types and seasons, with free-living amoebae (FLA), including Vermamoeba, Naegleria , and Echinamoeba predominating. Pathogenic taxa such as Naegleria fowleri and Acanthamoeba spp. were detected, including in treated waters. In parallel, 16S analyses showed that free-living bacterial populations, dominated by Salmonella, Klebsiella , and other Enterobacteriaceae, were compositionally distinct from the more diverse and resilient FLA-associated bacterial communities, enriched in Pseudomonas and Stenotrophomonas . These findings highlight how seasonality and disinfection shape microbial ecosystems in tropical DWDS, enabling the persistence of potentially pathogenic FLA and their bacterial endosymbionts. This study underscores the ecological and public health relevance of microbial host–pathogen interactions in engineered aquatic environments, and points to the need for integrative surveillance approaches to protect drinking water safety in climate-vulnerable regions.