Temporal dynamics in the bacterial abundances in Indian Sundarbans: unveiling the influence of reverse migration under the effects of the COVID-19 pandemic

The Sundarbans, a vital ecosystem in the Ganges Delta, faces multifaceted challenges exacerbated by climate change and socio-economic factors. This study investigates the impact of COVID-19 pandemic induced reverse migration on the microbial dynamics of the Indian Sundarbans using metagenomics guided wastewater surveillance.Samples were periodically collected once in a year over a span of three years with one-year interval between each sampling event. The sampling years- 2019, 2021 and 2023 were categorised as Pre- COVID-19, Mid-COVID-19 and Post-COVID-19 periods respectively. Following sampling, thorough metagenomic profiling was conducted to evaluate temporal dynamics in bacterial abundances amidst pandemic.16S metagenomic sequencing revealed the dominance of the members of phylum Proteobacteria in all the three samples. Sample collected during the Mid-COVID period exhibited a distinct enrichment of antibiotic resistance pathways, potentially linked to the influx of migrant workers with limited healthcare access and potential reliance on self-medication. Interestingly, during the peak of the pandemic, the abundance of opportunistic pathogens like Pseudomonas and Acinetobacter in the wastewater decreased compared to pre- and post-pandemic levels. Conversely, Sphingomonas associated with respiratory infections, showed a surge during the mid-COVID period. Agricultural practices adopted during the lockdown could explain the observed rise in nitrogen-fixing bacteria like Methylotenera and Rhizobium in the Mid-COVID sample.As reverse migration reshapes demographic patterns, proactive measures are needed to mitigate health risks and sustain ecosystem health. Additionally, it would highlight the utility of metagenomics-guided surveillance in informing public health policies amidst dynamic socio-economic and environmental changes.