A comparative analysis of the metagenomes from two 30 000-year-old permafrost samples, one of lake-alluvial origin and the other from late Pleistocene Ice Complex sediments, revealed significant differences within microbial communities. The late Pleistocene Ice Complex sediments (which have been characterized by the absence of methane with lower values of redox potential and Fe2+ content) showed a low abundance of methanogenic archaea and enzymes from both the carbon and nitrogen cycles, but a higher abundance of enzymes associated with the sulfur cycle. The metagenomic and geochemical analyses described in the paper provide evidence that the formation of the sampled late Pleistocene Ice Complex sediments likely took place under much more aerobic conditions than lake-alluvial sediments.

This work was supported by grants from the Russian Scientific Fund (14-14-01115) to Elizaveta Rivkina; from the National Science Foundation (DEB-1442262) to Tatiana Vishnivetskaya; and from the HHMI International Early Career Scientist Program (55007424), the EMBO Young Investigator Programme, MINECO (BFU2012-31329 and Sev-2012-0208), and the AGAUR program (2014 SGR 0974) to Fyodor Kondrashov. Support from the Russian Scientific Fund (14-14-01115) was allocated for sample collection, gDNA isolation, and analysis of metagenomic data.