MICROBIAL COMMUNITIES IN FERROMANGANESE DEPOSITS IN FORT STANTON CAVE, NM, USA ARE SIGNIFICANTLY DIFFERENT FROM SURFACE SOIL COMMUNITIES

Deep arid-land carbonate caves receive limited surface input; hence, critical constituents (e.g. C_org and NH₄⁺) required for microbial communities are often found in low quantities. We examined the archaeal and bacterial makeup of low-nutrient soil-like material (speleosol), rich in Fe- and Mn-oxides, occurring on the walls and ceilings of Snowy River in Fort Stanton Cave, NM, USA, a carbonate cave, and in corresponding overlying surface soils. Results of Illumina mi-seq sequencing of the 16S rRNA gene indicate that the bacterial and archaeal communities in the cave are significantly dissimilar taxonomically from their surface counterparts. Core microbiome results, representing operational taxonomic units (OTUs) occurring in not less than 80% of all samples, determined that there were only 19 archaeal and 17 and bacterial OTUs shared between surface and cave samples. The surface archaeal community was primarily represented by the Thaumarchaeota class Soil Crenarchaeotic Group (SCG), while dominant archaeal groups in the subsurface included the Euryarchaeota class Thermoplasmata and the Thaumarchaeota classes South African Gold Mine Gp 1 (SAGMCG-1), Marine Group I (MGI), and AK31. Bacterial cave OTUs significantly different from surface bacteria included the phyla Nitrospirae, GAL15, Omnitrophica, RBG-1 (Zixibacteria), Latescibacteria, SBR1093, and Ignavibacteriae. Our results provide taxonomic evidence that Fort Stanton Cave provides a biological niche for cave-adapted oligotrophic/chemolithotrophic bacterial and archaeal groups, and that the microbial community composition is likely influenced by depth below the surface and rock geochemistry. Remote cave communities such as these provide key insights into how microorganisms adapt to the subsurface.