Shifts in Bacterial Community Composition and Functional Traits at Different Time Periods Post-deglaciation of Gangotri Glacier, Himalaya

Climate change causes an unprecedented increase in glacial retreats. The melting ice exposes land for colonization and diversification of bacterial communities leading to soil development, changes in plant community composition, and ecosystem functioning. Although a few studies have focused on macro-level deglaciation impacts, little is known about such effects on the bacterial community succession. Here, we provide meta-barcoding-based insight into the ecological attributes of bacterial community across different retreating periods of the Gangotri glacier, western Himalaya. We selected three sites along a terminal moraine representing recent (~ 20 yrs), intermediate (~ 100 yrs), and late (~ 300 yrs) deglaciation periods. Results showed that the genus Mycobacterium belonging to phylum Actinobacteria dominated recently deglaciated land. Relative abundance of these pioneer bacterial taxa decreased by 20-50% in the later stages with the emergence of new and rising of the less abundant members of the phyla Proteobacteria, Firmicutes, Planctomycetes, Acidobacteria, Verrucomicrobia, Candidatus TM6, and Chloroflexi. The community in the recent stage was less rich and harbored competitive interactions, while the later stages experienced a surge in bacterial diversity with cooperative interactions. The shift in α-diversity and composition was strongly influenced by soil organic carbon, carbon to nitrogen ratio, and soil moisture content. The functional analyses revealed a progression from a metabolism focused to a functionally progressive community required for bacterial co-existence and succession in plant communities. Overall, the findings indicate that the bacterial communities inhabit, diversify, and develop specialized functions post-deglaciation leading to nutrient inputs to soil and vegetation development, which may provide feedback to climate change.