Seasonal and Source-Associated Microbiome Dynamics in Brazilian Drinking Water

Bacterial diversity in drinking water is remarkably high and can reveal source-specific microbial signatures that serve as potential indicators of contamination. In this study, we analyzed the bacterial diversity in drinking water from surface and groundwater sources in Ouro Preto, Brazil, across two seasons (rainy and dry), using 16 S rRNA gene-based next-generation sequencing. The bacterial diversity and taxonomic composition were similar in surface water sources across seasons. In contrast, the diversity and bacterial community structure of groundwater sources showed significant seasonal variation, with Firmicutes (Bacilli class) predominating in the dry season, while Proteobacteria, particularly Betaproteobacteria, dominated in most sources. Associations between bacterial classes and water quality parameters highlighted Bacteroidia, Clostridia, Gammaproteobacteria, and Flavobacteriia as strongly linked to organic pollution indicators. Bacilli were negatively correlated with pH and dissolved oxygen (DO), whereas Nitrospira and Acidobacteria were negatively associated with pH and DO, but positively with arsenic and nitrate concentrations. Conversely, Alpha- and Betaproteobacteria, as well as Cytophagia, were associated with surface water sources presenting favorable physicochemical parameters, such as oxidation-reduction potential (ORP), pH, and DO. Several operational taxonomic units (OTUs), including Bacillus, Enterococcus, Ralstonia, and Acinetobacter, correlated with heavy metal presence. Importantly, 16 S rRNA gene sequencing infers bacterial presence, but not activity or pathogenic potential; however, it provides valuable insights into the dynamics of microbial populations in relation to different physicochemical parameters.