Drivers of the diversity and composition of endolithic microbial communities in the hyperarid Atacama desert

The expansion of desertification across our planet is accelerating as a result of human activity and global climate change. In hyper-arid deserts, microbial communities colonized the rocks' interior (endoliths) as a survival strategy and are often considered at the end point of desiccation. Yet, the structure and composition of endolithic microbial communities and the drivers promoting their assembly in such remoted areas are still poorly unexplored. Using a sampling strategy that minimized climate regime and biogeography effects, we analyzed the diversity and community composition of endolithic microbial communities of 4 different lithic substrates – calcite, gypsum, ignimbrite and granite – found in the hyper-arid Atacama Desert. By combining microscopy, mineralogy and high throughput sequencing, we found endolithic microbial communities' diversity and composition highly specific to their substrates, indicating a fine diversification of the microbial reservoir. We propose that the architecture of the rock, i.e. the space available for colonization, is linked to light penetration and water retention capabilities and is ultimately a driver of the diversity and composition of endolithic communities at the dry limits of life