Functional genetic potential of benthic microbial mat communities in Arctic, Antarctic, and sub-Antarctic lakes.

Benthic microbial mat communities are key drivers of ecosystem functioning in polar lakes and ponds, forming the base of aquatic food webs and contributing substantially to nutrient cycling. Although Arctic, sub-Antarctic, and Antarctic microbial mats differ in community composition, their functional genetic potential remains poorly understood. We applied shotgun metagenomic sequencing to study 17 microbial mat communities from Arctic and (sub-)Antarctic lakes differing in salinity, catchment vegetation, and climatic conditions. Stress response genes, especially cold stress, and phosphorus cycling and metabolism genes were highly abundant in all lakes. A large proportion of functional genes was shared between regions, with core functions dominated by transport mechanisms and energy production. However, clear differences in particular gene abundances were observed. Several East-Antarctic lakes and inland ponds in the Transantarctic Mountains showed a dominance of oxygenic photosynthesis and Calvin cycle genes for carbon fixation, likely reflecting the dominance of Cyanobacteriota. In Arctic and sub-Antarctic lakes with catchment vegetation and higher arthropod abundances, lignin and chitin degradation genes were more important. Our study shows that, despite distinct biogeographic patterns in community composition, the functional genetic potential of polar lake microbial mats mainly reflects climatic and local environmental conditions, emphasizing specific adaptations to extreme polar environments.