Phylogenetic Composition of Rocky Mountain Endolithic Microbial Ecosystems

Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309-0347; Center for Astrobiology, University of Colorado at Boulder, CO 80309-0392

^* To whom correspondence should be addressed. Email: nrpace{at}colorado.edu.

	Abstract

The endolithic environment, the pore space in rocks, is a ubiquitous microbial habitat. Photosynthesis-based endolithic communities inhabit the outer millimeters to centimeters of rocks exposed to the surface. Such endolithic ecosystems have been proposed as simple, tractable models for understanding basic principles in microbial ecology. In order to test previously conceived hypotheses about endolithic ecosystems, we studied selected endolithic communities in the Rocky Mountain region of the United States with culture-independent molecular methods. Community compositions were determined by ribosomal RNA gene sequence content, and communities were compared with statistical phylogenetic methods. Results indicate endolithic ecosystems are seeded from a select, global metacommunity and form true ecological communities that are among the simplest microbial ecosystems known. Statistical analysis shows that biogeographical characteristics that control community composition, such as rock type, are more complex than predicted. Collectively, results from this study support the idea that patterns of microbial diversity found in endolithic communities are governed by principles similar to those observed in macro-ecological systems.