Sun exposure drives Antarctic cryptoendolithic community structure and composition

The harsh environmental conditions of the ice-free regions of Continental Antarctica are considered one of the closest Martian analogues on Earth. There, rocks play a pivotal role as substratum for life and endolithism represents a primary habitat for microorganisms when external environmental conditions become incompatible with active life on rock surfaces, allowing life to spread throughout these regions with extreme temperatures and low water availability. Previous research concluded that altitude and distance from sea do not play as driving factors in shaping microbial abundance and diversity, while sun exposure was hypothesized as significant parameter influencing endolithic settlement and development. With this in mind, eight localities were visited in the Victoria Land along an altitudinal transect from 834 to 3100 m a.s.l. and 48 differently sun-exposed rocks were collected. We explored our hypothesis that changes in sun exposure translate to shifts in community composition and abundances of main biological compartments (fungi, algae and bacteria) using Denaturing Gel Gradient Electrophoresis and quantitative PCR techniques. Major changes in community composition and abundance occurred between north and south sun-exposed samples. As Antarctic endolithic ecosystems are extremely adapted and specialized but scarcely resilient to external perturbation, any shifts in community structure may serve as early-alarm systems of climate change; our findings will be of wide interest for microbial ecologists of extreme environments such as arid and hyper-arid area.