Microbial colonisation of chasmoendolithic habitats in the hyper-arid zone of the Atacama Desert

Efforts in searching for microbial life in the driest part of Atacama Desert, Chile, revealed a small number of lithic habitats that can be considered as environmental refuges for life. In this study, we describe for the first time chasmoendolithic colonisation of fissures and cracks of rhyolite-gypsum and calcite rocks collected in the hyperarid zone of the desert. The use of high-throughput sequencing revealed that the Atacama rock communities comprised a few dominant phylotypes and a number of less abundant taxa representing the majority of the total community diversity. The chasmoendolithic communities were dominated by Chroococcidiopsis species cyanobacteria and supported a number of heterotrophic bacterial lineages. Micro-climate data and geomorphic analysis of the mineral substrates suggested higher water availability in the calcite rocks in the form of enhanced water retention in the complex network of cracks and fissures of these rocks as well as increased occurrence of liquid water in the form of dewfall. These characteristics were associated with a diverse community of phototrophic and heterotrophic bacteria in the calcite chasmoendolithic ecosystem. This study is another example of the diversity of adaptive strategies at the limit for life and illustrates that rock colonisation is controlled by a complex set of factors.