Chapter 7 - Endolithic microbial communities as model systems for ecology and astrobiology

Abstract

Microbial communities play a critical role in all key nutrient cycles on Earth and even more so in deserts where plants are scarce or even totally absent. In the most arid deserts, microbial communities find refuge inside translucent rocks (endoliths) as a survival strategy. Since the work of E. Imre Friedmann on microbial communities in the Dry Valleys of Antarctica, lithic communities have been described from most hot and cold hyperarid deserts around the world, and from multiple substrates. Yet, their diversity, metabolic activities, and interactions with their rocky habitat remain vastly unexplored. Here, we discuss the lithic habitat and explore the colonization strategies evolved by lithic microorganisms. We report that while recent studies have revealed the exceptional taxonomic and functional diversity of these highly adapted microbial communities, little is known about their in situ metabolic activities, interactions between community members, and the role of viruses in community dynamics. To address what factors impact the assembly of endolithic communities, we present the concept of “rock architecture,” that is, the space available for colonization, which, linked to light penetration and water retention, is ultimately a driver of community diversity and composition. Finally, we discuss how the study of microbial communities from hyperarid deserts can further our understanding of the dry limits for life as we know it and provide insights into the habitability of extraterrestrial environments.