This project will provide additional knowledge to formulate answer for a major unresolved question in microbial ecology of permanently frozen sediments  - whether microbes recovered from deep permafrost sediments are living fossils, representing an ancient surface community preserved through time, or an active extant community that has been interacting and evolving continuously since becoming buried. The current study will deliver a resolution of this debate, which is critically important for determining past versus present microbial diversity in deep sediments and also in determining molecular evolution within bacterial taxa.

The main goal of the project is to understand how transitions from the active layer to permafrost, and from young permafrost to old permafrost influence taxonomic and functional diversity. The diverse metabolic pathways active in cryosols are expected to slow down in subfreezing permafrost leading to changes in activity of the intact microbial community and functional diversity, followed by changes in genetic and taxonomic diversity over time. Carefully selected permafrost sediments with known ages and microorganisms embedded within the permafrost since time of freezing provided a strong basis for this research.

Vishnivetskaya and colleagues finished their first field season in Kolyma-Indigirka lowland, northeast Siberia. Upper cryosol and deep subsurface permafrost samples were collected from drilling boreholes located near the Alazeya River. The permafrost cores were recovered from two deep boreholes (20 to 25 m). The deeper borehole was located on river floodplain and penetrated young river sandy-alluvial sediments, as well as old sediments of Olyor Suite (0.6 to 1.8 Ma years old) and Thomus-Yar Suite (2.0-3.0 Ma years old). The ice-rich silty loams of the Yedoma Suite (30-40 Ka years old) were collected from borehole located on the cliff approximately 30 m in elevation from the river level. In total, 45 meter of permafrost core was recovered and 132 frozen samples were collected using a high quality controlled technique for microbiological and molecular analyses; while 50 samples each were collected for geochemical analyses and iciness estimation. An additional 89 samples were degassed in the field for gases determination, particularly CO2 and CH4.

The major goals of the project:

Goal 1: Assess the metagenomic diversity of permafrost sediments with different freezing ages, or samples of the same freezing age but different origin.

Goal 2: Determine which microbial community members in young and old permafrost samples are metabolically active within the permafrost strata.

Goal 3: Determine the level of variation between genomes from 3 Ma ancient and 30 Ka young permafrost and modern sediment samples.

Goal 4: Determine whether the combined data support that microbial communities in permafrost sediments are best represented as a fossil archive (extinct), a contemporary community (extant) or a mixed model.