Metagenomic analysis of a mega-city river network reveals microbial compositional heterogeneity among urban and peri-urban river stretch.

The rivers in the megacities face a constant inflow of extremely polluted wastewaters from various sources, and their influence on the connected peri-urban river is still poorly understood. The riverine system in Pune consists of Rivers Mula, Ramnadi, Pawana, Mutha, and Mula-Mutha, traversing through the urban settlements of Pune before joining River Bhima in the peri-urban region. We used MinION-based metagenomic sequencing to generate a comprehensive understanding of the microbial diversity differences between the urban and peri-urban zones, which has not been explored at the meta scale until date. The taxonomic analysis revealed significant enrichment of pollution indicators microbial taxa (Welsch's t-test, p < 0.05, Benjamini-Hochberg FDR test) such as Bacteriodetes, Firmicutes, Spirochaetes, Synergistetes, Euryarcheota in the urban waters as compared to peri-urban waters. Further, the peri-urban waters showed a significantly higher prevalence of ammonium oxidising archaeal groups such as Nitrososphaeraceae (Student's t-test p-value <0.05 with FDR correction), thereby probably suggesting the influence of agricultural runoffs. Besides, the microbial community diversity assessment also indicated the significant dissimilarity in the microbial community of urban and peri-urban waters. Overall, the analysis predicted 295 virulence genes mapping to 38 different pathogenic bacteria in the riverine system. Moreover, the higher genome coverage (at least 60%) for priority pathogens such as Pseudomonas, Klebsiella, Acinetobacter, Escherichia, Aeromonas in the sediment metagenome consolidates their dominance in this riverine system. To conclude, our investigation showed that the unrestrained anthropogenic and related activities could potentially contribute to the overall dismal conditions and influence the connected riverine stretches on the outskirts of the city.