Abstract
Background: Total DNA (intracellular, iDNA and extracellular, eDNA) from ancient permafrost records the mixed genetic repository of the past and present microbial populations through geological time. Given the exceptional preservation of eDNA under perennial frozen conditions, typical metagenomic sequencing of total DNA precludes the discrimination between fossil and living microorganisms in ancient cryogenic environments. DNA repair protocols were combined with high throughput sequencing (HTS) of separate iDNA and eDNA fraction to reconstruct metagenome-assembled genomes (MAGs) from ancient microbial DNA entrapped in Siberian coastal permafrost. Results: Despite the severe DNA damage in ancient permafrost, the coupling of DNA repair and HTS resulted in a total of 52 MAGs from sediments across a chronosequence (26–120 kyr). These MAGs were compared with those derived from the same samples but without utilizing DNA repair protocols. The MAGs from the youngest stratum showed minimal DNA damage and thus likely originated from viable, active microbial species. Many MAGs from the older and deeper sediment appear related to past aerobic microbial populations that had died upon freezing. MAGs from anaerobic lineages, including Asgard archaea, however exhibited minimal DNA damage and likely represent extant living microorganisms that have become adapted to the cryogenic and anoxic environments. The integration of aspartic acid racemization modeling and metaproteomics further constrained the metabolic status of the living microbial populations. Collectively, combining DNA repair protocols with HTS unveiled the adaptive strategies of microbes to long-term survivability in ancient permafrost. Conclusions: Our results indicated that coupling of DNA repair protocols with simultaneous sequencing of iDNA and eDNA fractions enabled the assembly of MAGs from past and living microorganisms in ancient permafrost. The genomic reconstruction from the past and extant microbial populations expanded our understanding about the microbial successions and biogeochemical alterations from the past paleoenvironment to the present-day frozen state. Furthermore, we provided genomic insights into long-term survival mechanisms of microorganisms under cryogenic conditions through geological time. The combined strategies in this study can be extrapolated to examine other ancient non-permafrost environments and constrain the search for past and extant extraterrestrial life in permafrost and ice deposits on Mars. [MediaObject not available: see fulltext.].
Original language | English |
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Article number | 110 |
Journal | Microbiome |
Volume | 9 |
Issue number | 1 |
DOIs | |
State | Published - Dec 2021 |
Funding
This research was supported by an NSF DEB-1442059 and NSF EAR-1528492 to TCO, NSF DEB-1442262, and NSF International Research Experience for Students grant IIA-1460058 to TAV, U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Genomic Science Program under Award Number DE-SC0020369 to KGL and by Russian Government Assignment AAAA-A18-118013190181-6 and RFBR 19-29-05003 to EMR. Authors thank undergraduate student Molly Moran, participant of the NSF International Research Experience for Students project, for technical help.
Funders | Funder number |
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National Science Foundation | IIA-1460058, DEB-1442059, DEB-1442262, EAR-1528492 |
U.S. Department of Energy | |
Office of Science | |
Biological and Environmental Research | AAAA-A18-118013190181-6, DE-SC0020369 |
Russian Foundation for Basic Research | 19-29-05003 |
Keywords
- Adaptive strategy
- Ancient permafrost
- Asgard archaea
- Fossil and living microorganisms
- Long-term survivability
- Metagenome-assembled genome