Metagenômica aplicada ao estudo de água doce destinada ao consumo humano no município de Ouro Preto, Minas Gerais

Abstract

Surface freshwater and groundwater are important aquatic ecosystems that harbor complex microbial diversity and are often used as drinking water. Therefore, the study of the microbiome of these waters is relevant, because it is directly related to public health. Metagenomics, particularly 16S rDNA sequencing has been employed to investigate the procaryotic community of drinking water sources, promoting a better understanding of the structure and autochthonous procaryotic dynamics of the environment. Considering the relevance of the subject this study aimed to determine the taxonomic composition and diversity of the procaryotic community of groundwater and surface water sources used for human consumption and community dynamics in the drinking water treatment system of the municipality of Ouro Preto, Brazil. Water samples were filtered (0.22 μm pore size) and DNA was extracted from the membranes using a commercial kit. Sequencing of the V4 region of the 16S rDNA was performed by Illumina Miseq and the generated sequences were processed and clustered into OTUs (97% identity). Surface water sources exhibited similar procaryotic diversity and composition showing no seasonality. However, groundwater sources showed a significant increase in diversity in the rainy season and differences in procaryotic composition between seasons. The phylum Proteobacteria, class Betaproteobacteria, OTU Comamonadaceae not classified, predominated in freshwater sources used for alternative and public supply, except for groundwater in the dry season in which Firmicutes, class Bacilli, particularly Bacillus and Enterococcus, were detected in a higher abundance. In regard to physicochemical characteristics, a significant positive correlation was observed between Bacteroidia, Clostridia, Gammaproteobacteria, and Flavobacteria taxa with parameters that indicate organic pollution and Alphaproteobacteria, Betaproteobacteria, and Cytophagia with parameters that indicate suitable water. In addition, several OTUs were significantly correlated with heavy metals, among them Acinetobacter, Bacillus, and Enterococcus. Relevant potentially pathogenic bacteria such as Acinetobacter baumannii and Escherichia coli were detected in water sources used for public and alternative supply, representing a potential risk to the population, especially for those not submitted to treatment. Water treatment changed community structure. While phylum Proteobacteria, class Betaproteobacteria, predominated in raw water, phylum Firmicutes, class Bacilli, Geobacillus, Bacillaceae unclassified, Enterococcus, Bacillales unclassified, and Paenibacillus OTUs were dominant in treated water samples (post-treated and tap water). Reduction of procaryotic diversity indexes and 16S rDNA count confirms the effect of treatment on the microbial community of raw water. The detection of potentially pathogenic bacteria such as Enterococcus faecalis, Mycobacterium intracellulare and A. baumannii throughout the distribution system, indicating their persistence consequently to the resistance to treatment processes raises particular concern.