Characterizing Microbial Communities in >7000- and >180,000-Year-Old Antarctic Permafrost Using a Low-Biomass Decontamination Protocol

The McMurdo Dry Valleys may harbor diverse surface microbial communities, yet little is known about subsurface microorganisms in permafrost and their potential for paleoecological reconstruction. Here, we present microbial diversity and paleoecology from lower Wright Valley (7000- to 25,000-year-old) and Pearse Valley (>180,000-year-old) permafrost habitats in the McMurdo Dry Valleys. Using a new decontamination protocol, low-biomass extraction approaches, and 16S ribosomal RNA gene amplification sequencing, we assessed microbial community structure and diversity. The difference between surface and subsurface microbial communities at both lower Wright and Pearse valleys suggests the environmental conditions were different at the time of colonization. Microbial taxa identified in subsurface permafrost but not in the surface soil in both valleys indicate an ancient and isolated microbial community. In contrast, communities were not resolved at a high-elevation site in the stable upland zone, the Friis Hills (>6 Ma). The inability to identify DNA using amplicon sequencing in the Friis Hills is consistent with previous efforts to analyze high-elevation soils and permafrost, which suggests that microbial habitability is severely restricted in persistent cold, arid habitats. Therefore, utilizing other approaches may be necessary to analyze surface and subsurface permafrost on Earth, and perhaps Mars, where low-abundance microbial populations may be present.