Astrobiology Science Conference 2017 (LPI Contrib. No. 1965) 3693.pdf

MICROBIAL COMMUNITY STRUCTURE, METABOLISM AND FUNCTION IN BASALTIC CAVES AND LAVA TUBES E. Zaikova1, S. Fuqua2, S.S. Hughes3, S. Kobs Nawotniak3, W. B. Garry4, D. S. S. Lim5, J. Heldmann5. S. S. Johnson1. 1Department of Biology, Georgetown University, ([email protected]); 2Washington University in St Louis; 3Idaho State University; 4NASA Goddard Space Flight Center; 5NASA Ames Research Center

Background: Subsurface environments provide stable taxonomic and functional analysis. Microbial commu- conditions and shield microbial life from radiation and nity structure was investigated using 16S rRNA gene temperature fluctuations, allowing life to evolve and amplicon sequencing, and community metabolic poten- persist in otherwise harsh conditions. Importantly, the tial, genetic content and identity of microbial groups as- relative stability in environmental parameters of sociated with sulfur, carbon and metal metabolism were subsurface habitats also permit the preservation of assessed using metagenomics. Microbial abundance and evidence of past and current biological activity. identity of active community members is currently un- Consequently, lava tubes and basaltic caves observed on derway using qPCR and cDNA amplicon sequencing Mars may potentially be significant targets for study targeting the 16S rRNA gene. while searching for signs of martian life. Volcanic Results and Discussion: Our initial taxonomic analysis environments on Earth, such as the iron-rich basalts has revealed that the microbial community associated found at Craters of the Moon (COTM) in Idaho (analogs with sulfate deposits in small cavities along the wall of to martian basalts in terms of composition), can be used a cave as described in [1,2] is diverse, encompassing 22 as analogs to understand microbial metabolism, . These phyla consisted of aerobic, mi- community composition and biosignature preservation croaerophilic and anaerobic organisms with potential (secondary mineral assemblages, for example). roles in metal oxidation as well as S and N cycling. Ac- Secondary sulfate and carbonate mineral deposits tinobacteria was the most abundant phylum, represent- are found in lava tubes and caves of all sizes in the Blue ing 58% of the community, and included the extremo- Dragon flow within COTM [1]. The deposits occur in philic lineages Rubrobacteria and Thermoleophilia. small cavities on cave walls and ceilings, as well as The Class Rubrobacteria contains thermophilic, radia- larger localized mounds on the cave floor [1]. Abiotic tion and desiccation-resistant species [3]; Rubrobacte- origins for these secondary deposits have been ria species have also been detected in sulfidic metal tail- proposed, however, peaks observed by FTICR-MS ings, where they were associated with soluble sulfate indicated association of biogenic organic compounds [4]. Three million pairs of high quality paired-end met- with secondary sulfate deposits, linking these minerals, agenomics reads were generated for this deposit. Func- directly or indirectly, to biological activity [2]. These tional analyses to probe possible Rubrobacteria roles in observations, together with sulfur isotope fractionation sulfur metabolism in basalt cave secondary minerals are results, led to the hypothesis that biological activity underway. , primarily alpha-proteobac- contributes to secondary mineral deposit formation [2]. teria affiliated with Sphingomonadales, , Specifically, [2] proposed that microbes may mediate , and were the other major oxidation of pyrite, one of the most abundant metal phyla. Analysis is ongoing, but these results open a win- sulfides in basalt, to sulfate through multiple dow into the microbial ecology and biogeochemistry of intermediates and subsequent precipitation [2]. secondary mineral deposits in basalt caves, and estab- Oxidation of sulfidic compounds is an important en- lish the site as a terrestrial analogue for modeling the ergy source for sulfur oxidizing bacterial species and biotic potential of subsurface environments on Mars. could help support a microbial community. However, it is not known whether organisms capable of sulfide oxi- dation are present in proximity to the deposits or what other microbes, and metabolisms, are found in the min- erals. We use next generation sequencing to identify mi- crobial organisms associated with secondary mineral deposits, delineate physiologically active members of the community and describe their potential metabolic roles. Methods: Samples collected for nucleic extraction

were either stored in a nucleic acid preservation buffer References: [1] Richardson C. D. et al. (2013) IJA, 12, or placed in a LN-primed cryoshipper immediately fol- 357–368.[2] Richardson C. D. et al (2012) P&SS, 65, lowing collection for transport to the lab, where they 93–103. [3] Shivlata L. and Satyanarayana T. (2015) were stored at -80°C until processing. Extracted nucleic FrontMicrobiol, 6, 1014. [4] Li X., et al (2015) SciRep, acids were prepared for sequencing on an Illumina 5, 12978. MiSeq, and the resulting sequence data were subject to