Host Identity Shapes Bacterial Community Structure and Their Metabolic Potential in Antarctic Terrestrial Ecosystem

Antarctic cryptogams and soils harbour diverse microbial communities that are fundamental to nutrient cycling and ecosystem resilience. However, the functional roles of these communities are not yet fully understood. This study investigated the bacterial communities associated with the moss Andreaea regularis, the lichen Usnea aurantiacoatra and adjacent soils in Antarctica. Metagenomic analysis revealed clear host-dependent structuring of microbial communities, with moss and soil supporting diverse and metabolically versatile assemblages, while the lichen harbored a smaller and more specialized bacterial community. Community composition exhibited significant variation among substrates, with U. aurantiacoatra dominated by Pseudomonadota and a narrow set of cyanobacteria (particularly Leptolyngbyales), whereas A. regularis and soils contained richer, more even assemblages dominated by Pseudomonadota, Actinomycetota and Cyanobacteriota. Functional profiling revealed that soil bacteria possessed the broadest metabolic potential, including a complete nitrogen cycle and multiple nutrient uptake pathways, whereas the lichen microbiome showed the most reduced representation of important metabolic pathways.