Metagenomic analysis of microbiome spatial dynamics in urban river confluence affected by city wastewater

Environmental pollutants have a profound impact on microbial dynamics. This study highlights the influence of anthropogenic activity on the shift in bacterial diversity in the catchment area compared to upstream and downstream at Kathajodi, using a metagenomic approach for the first time in River Kathajodi.

Water samples were collected from upstream, catchment, and downstream locations and transported at 4°C to the laboratory for DNA extraction, library preparation, sequencing, and physicochemical analysis employing inductively coupled plasma. The extracted DNA was sequenced via the Illumina HiSeq platform and analyzed through MG-RAST for taxonomic and functional classification using KEGG and COG annotations. Statistical diversity analysis, including rarefaction curves, alpha- and beta-diversity indices, and Venn diagrams, provided insights into microbial composition and community variations across sites.

A significant abundance of pollution indicator members of phylum Bacteroidetes (29.82%) in the catchment (CM), highly contaminated with metals, fecal, and other organic pollutants, could be attributed to their high metabolic capabilities to degrade them. The pristine upstream (US) exhibited an abundance of Shewanella (25.04%), Pseudomonas (17.35%), and Synechococcus (5.62%). The CM, influenced by high anthropogenic activity, showed higher abundances of Flavobacterium (5.20%), Arcobacter (4.05%), and Bacteroides (3.88%). In contrast, downstream (DS), with fewer anthropogenic activities, displayed higher abundances of Aeromonas (4.40%), Acidovorax (0.52%), and Acidimicrobium (0.32%). The highest bacterial diversity of CM could be due to the influence of the physicochemical properties of city waste effluent. From the Venn diagram, 73 common OTUs at the genera level were observed in all three sites, which indicates that the native microflora of the river water niche remains unaffected irrespective of the temporary changes in the vicinity. The functional profiling through KEGG and COG revealed that CM was enriched in carbohydrate metabolism (12.11%), while DS exhibited higher contributions to amino acid metabolism, along with the highest relative abundance of general function prediction (R) (12.89%), all indicative of stress adaptation and metabolic flexibility under polluted conditions. The clean upstream is home to oxygen-loving helpful bacteria, the catchment supports nutrient-hungry and sewage-linked microbes, while the downstream is dominated by metal-tolerant and possibly harmful bacteria, showing the clear impact of human activities along the river.

The marked shift in bacterial diversity between US, CM, and DS regions highlights the ecological consequences of anthropogenic impact. These findings emphasize the need for effective environmental management to safeguard water quality and prevent undesirable health issues.