World's Largest Mass Bathing Event Influences the Bacterial Communities of Godavari, a Holy River of India.

Kumbh Mela is one of the largest religious mass gathering events (MGE) involving bathing in rivers. The exponential rise in the number of devotees, from around 0.4 million in 1903 to 120 million in 2013, bathing in small specified sites can have a dramatic impact on the river ecosystem. Here, we present the spatiotemporal profiling of bacterial communities in Godavari River, Nashik, India, comprising five sites during the Kumbh Mela, held in 2015. Assessment of environmental parameters indicated deterioration of water quality. Targeted amplicon sequencing demonstrates approximately 37.5% loss in microbial diversity because of anthropogenic activity during MGE. A significant decrease in phyla viz. Actinobacteria, Chloroflexi, Proteobacteria, and Bacteroidetes was observed, while we noted substantial increase in prevalence of the phylum Firmicutes (94.6%) during MGE. qPCR estimations suggested nearly 130-fold increase in bacterial load during the event. Bayesian mixing model accounted the source of enormous incorporation of bacterial load of human origin. Further, metagenomic imputations depicted increase in virulence and antibiotic resistance genes during the MGE. These observations suggest the striking impact of the mass bathing on river ecosystem. The subsequent increase in infectious diseases and drug-resistant microbes pose a critical public health concern.