Fine scale diversification of endolithic microbial communities in the hyper-arid Atacama Desert

ABSTRACT The expansion of desertification across our planet is accelerating as the result of human activity and global climate change. In hyper-arid deserts, endolithic microbial communities colonize the rocks’ interior as a survival strategy. Yet, the composition of these communities and the drivers promoting their assembly are still poorly understood. Using a sampling strategy that minimized climate regime and biogeography effects, we analyzed the diversity and community composition of endoliths from four different lithic substrates – calcite, gypsum, ignimbrite and granite – collected in the hyper-arid zone of the Atacama Desert, Chile. By combining microscopy, mineralogy, and high throughput sequencing, we found these communities to be highly specific to their lithic substrate, although they were all dominated by the same four main phyla, Cyanobacteria , Actinobacteria , Chloroflexi and Proteobacteria . This finding indicates a fine scale diversification of the microbial reservoir driven by substrate properties. Our data suggest that the overall rock chemistry is not an essential driver of community structure and we propose that the architecture of the rock, i.e . the space available for colonization and its physical structure, linked to water retention capabilities, is ultimately the driver of community diversity and composition at the dry limit of life. Originality-Significance Statement In this study, we demonstrated that endolithic microbial communities are highly specific to their substrates, suggesting a fine scale diversification of the available microbial reservoir. By using an array of rock substrates from the same climatic region, we established, for the first time, that the architecture of the rock is linked to water retention and is ultimately the driver of community diversity and composition at the dry limit for life.