New Mexico Geological Society Annual Spring Meeting — Abstracts

Dry desert caves contain unique microbial communities that survive in energy starved subterranean environments. These caves often contain slow-growing chemolithotrophic microorganisms that may utilize the chemical energy from inorganic sulfur, nitrogen, or metals in minerals and trace gases, and in the process might modify cave walls by slow carbonate dissolution or secondary mineral formation. In this study, we are using metagenomics to determine the identity and genomic potential of novel S and N cycling microorganisms from the walls of two arid cave systems, and explore their roles in the cave ecosystems. The first site, Lehman Caves, Nevada, is an ancient hypogene cave that might have experienced sulfuric acid corrosion more than 10 million years ago. The second, Lechuguilla Cave, is an ancient sulfuric acid cave that formed around 4-6 million years ago. We don’t expect these caves to have active sulfide oxidizing microbial populations, and instead hypothesize that, based on previous rRNA gene surveys, inorganic N compounds like ammonia and other trace gases are the primary source of energy for life in these oligotrophic settings. We initially generated two small preliminary metagenomes: one from a recent sample from Lehman Caves that generated 44 total megabase pairs (Mbp) of DNA sequence following quality filtering and trimming, and one collected more than 20 years ago from Lechuguilla Cave, which generated 219 Mbp of sequence. These metagenomes contained genes for carbon dioxide fixation, dissimilatory nitrogen oxidation, and manganese oxidation. Classification of conserved marker genes shows that they contain populations of previously undescribed microorganisms; however, they did not have sufficient depth of coverage to recover metagenome-assembled genomes (MAGs). We therefore generated a larger metagenome from a second sample from Lehman Cave, and were able to recover several high-quality MAGs. We will describe the genomic potential of these novel organisms, and discuss implications for energy resources and biogeochemistry of desert caves.