Exploring the allochthonous pollution influence on bacterial community and co-occurrence dynamics of River Ganga water through 16S rRNA-tagged amplicon metagenome.

River Ganga is one of the largest and most sacred rivers of India. This river is largely affected by anthropogenic activities causing significant increase in water pollution. The impact of drains discharging polluted water on the bacterial community dynamics in the river remains unexplored. To elucidate this, the targeted 16S rRNA V3-V4 variable region amplicon sequencing and bioinformatic analysis were performed using water from upstream, drain, and downstream of river Ganga. Analysis revealed significant difference in relative abundances of bacterial communities. The increase in bacterial abundance and alpha diversity was detected in the downstream compared to the upstream. Environmental factors were found significantly different between upstream and downstream water. At the phyla level, highly abundant taxa such as Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes, and Verrucomicrobia were observed. Bacterial genera like Prevotella, Bacteroides, Blautia, and Faecalibacterium (fecal indicator) had higher abundance in the downstream site. Network co-occurrence revealed that bacterial communities have a modular profile with reduced interaction in drain and downstream water. The network of co-occurring bacterial communities consists of 283 nodes with edge connectivity of 6900, 7074, and 5294 in upstream, drain, and downstream samples, respectively. Upstream communities exhibited the highest positive interaction followed by the drain and the downstream sites. Additionally, highly abundant pathogenic species such as Acinetobacter baumannii and Prevotella copri were also detected in all samples. This study suggests the drain to be allochthonous pollution vector that significantly contributes to bacterial community enrichment. From the results of this study, it is apparent that the lotic water may be used as the ecological reference to understand and monitor the variations in the bacterial communities and their co-occurrence dynamics in the fresh water ecosystems.