Microbial community dynamics from a fast-receding glacier of Western Himalayas highlight the importance of microbes in primary succession, nutrient recycling, and xenobiotics degradation

Climate change has caused an unimaginable upsurge in glacier retreats. The melted ice exposes bare areas offering sites for new ecosystem development where primary microbial succession initiates the build-up of organic mass for plant colonisation. Chhota Shigri glacier is one such glacier that has retreated immensely and provides an ideal site for microbial succession studies. Here, we studied the shift in microbial communities and their functional traits along the glacier forefield from bare glacier snout to mature vegetated foreland through amplicon and whole metagenome sequencing approaches. The forefield sites closer to the glacier snout were abundant in the microbial phyla, such as Patescibacteria, Gemmatimonadota, Proteobacteria, Bacteroidota, Chloroflexi, Cyanobacteria, Verrucomicrobiota and Myxococcota that have potential in carbon (C), nitrogen (N), and sulphur (S) cycling. The sites away from glacier snout were abundant in the phyla Actinobacteria and Acidobacteriota, which are heterotrophic and help in organic carbon recycling. The microbes at the sites closer to the glacier terminus were richer and more diverse than those away from the terminus. The abundance and diversity of the microbes were primarily affected by the local soil's temperature, followed by pH and elements concentration (Calcium (Ca), Phosphorous (P), Potassium (K), Iron (Fe), Copper (Cu), Zinc (Zn), Lead (Pb)). Moreover, the whole-genome metagenome study revealed the prevalence of genes associated with N, C and S cycling. Additionally, the microbes and genes involved in xenobiotics compounds (Aminobenzoate, Benzoate, Caprolactam) degradation are also observed in the forefield soils. This study pointed out microbial successional gradients, the effect of local environmental factors in driving microbial succession and the role of glacier microbes in nutrients cycling and xenobiotics degradation along glacier forefield, helping our understanding of microbial succession and functional roles played by the microbes at nutrient-poor glacial soil.