Extreme Niche Partitioning and Microbial Dark Matter in a Mauna Loa Lava Tube.

Mauna Loa (Hawaii Island, Hawaii); Hawaii

Lava tubes are key targets in the search for life on Mars. Their basaltic walls provide protection from radiation and changing environmental conditions, which could enable life or preservation of previous life in an otherwise harsh environment. We can understand the potential for Martian life in lava tubes by studying the habitability of analog environments on Earth. In this study, we present the first characterization of the microbial life inside a pristine Mauna Loa lava tube. This study is the first to combine 16S SSU rRNA sequencing and whole genome shotgun sequencing to map the taxonomic makeup and functional potential of any lava tube community in Hawaii, enabling a deep understanding of the types of microbes that thrive in this unique environment and the metabolisms they use. We find a surprisingly high degree of niche partitioning over small spatial scales and discuss implications for life detection strategies. Based on recent bioinformatic advancements in metagenomics, we also assemble dozens of high‐quality metagenome assembled genomes from the microbes living in the lava tubes, including several novel species. Plain Language Summary: In the search for life on Mars, lava tubes are targets for astrobiology. Lava tubes provide an underground shelter, protected from radiation and the harsh climate. Analog studies here on Earth can help us understand what types of microbes live in these terrains and how best to find them. In this study, we investigate the microbial communities in a previously unexplored lava tube on the Mauna Loa volcano in Hawaii. We set out to characterize the microbes that live there and what capabilities enable them to survive, such as how they acquire nutrients from their environment to produce energy. We collected mineral samples in the lava tube and sequenced the DNA that we found in the minerals. We used DNA sequences to identify which microbes are present as well as which metabolisms they can use. We found that there are significant differences in the microbial make‐up of each of the samples, even though some are taken within several centimeters of each other, with implications for how to assay a region of interest on Mars. We also found several novel species. Key Points: In this undisturbed environment, communities were characterized by multiple microniches, varying widely over the scale of metersThe lava tube contained high amounts of "microbial dark matter" or uncultivated microbes that remain unclassified in taxonomic databasesAlthough the mineralogy of many of the samples we studied was sulfate‐rich, metabolisms unrelated to sulfur dominated the metagenome [ABSTRACT FROM AUTHOR]

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