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In the context of global warming, the melting of Arctic permafrost raises the threat of a reemergence of microorganisms some of which were shown to remain viable in ancient frozen soils for up to half a million years. In order to evaluate this risk, it is of interest to acquire a better knowledge of the composition of the microbial communities found in this understudied environment. Here, we present a metagenomic analysis of 12 soil samples from Russian Arctic and subarctic pristine areas: Chukotka, Yakutia and Kamchatka, including nine permafrost samples collected at various depths. These large datasets (9.2 × 1011 total bp) were assembled (525 313 contigs > 5 kb), their encoded protein contents predicted, and then used to perform taxonomical assignments of bacterial, archaeal and eukaryotic organisms, as well as DNA viruses. The various samples exhibited variable DNA contents and highly diverse taxonomic profiles showing no obvious relationship with their locations, depths or deposit ages. Bacteria represented the largely dominant DNA fraction (95%) in all samples, followed by archaea (3.2%), surprisingly little eukaryotes (0.5%), and viruses (0.4%). Although no common taxonomic pattern was identified, the samples shared unexpected high frequencies of β-lactamase genes, almost 0.9 copy/bacterial genome. In addition to known environmental threats, the particularly intense warming of the Arctic might thus enhance the spread of bacterial antibiotic resistances, today's major challenge in public health. β-Lactamases were also observed at high frequency in other types of soils, suggesting their general role in the regulation of bacterial populations.

SummaryBackgroundAntimicrobial resistance is one of the major challenges affecting public health. It is mostly due to the continuous emergence of extended-spectrum β-lactamase from various environments followed by their rapid dissemination and selection in clinical settings. The warming of Earth’s climate is the other global threat facing human society, in particular with the Arctic regions experiencing a twice faster warming than the global average and permafrost affected by widespread thawing. A potentially dreadful combination of these two threats would be the release and dispersion of harmful microbes that have remained confined to largely uninhabited Arctic regions, or are stored dormant in permafrost.MethodsEnvironmental DNA was isolated from 12 soil samples from various Arctic and subarctic pristine regions in Siberia (Yakutia and Kamchatka), including nine permafrost samples collected at various depths. The large datasets obtained from high throughput sequencing was assembled in contigs and their protein-gene contents predicted. We used exhaustive similarity searches to perform taxonomical assignments of bacterial, archaeal, and eukaryotic organisms, as well as DNA viruses. In addition, we specifically identified β-lactamase genes and their prevalence per bacterial genome estimated through the detection of two universal single copy genes.FindingsA total of 9.217 1011 bp were exploited, leading to a total of 525,313 contigs at least 5kb in size. The DNA content of the various samples was found to be highly variable, not strictly correlated with the depth or radio-carbon-based deposit age, and most likely linked to the global density of microbes trapped in the corresponding permafrost layers. Bacteria account for more than 90% of the contigs in most samples, followed by Eukaryotes and Archaea (always lower than 10%). Viruses represented less than 2% of all contigs in all samples. The taxonomic profiles of surface cryosoils and deep permafrost samples exhibited a high diversity, including between permafrost samples originating from various depths in the same borehole. In all samples, bacterial contigs carrying different β-lactamases from class A to D were identified.InterpretationNo clear common taxonomic feature could be found shared by surface cryosoils or ancient permafrost layers. However, most samples (9/12) exhibited a high frequency of β-lactamase genes, with an estimated average close to 1 copy/bacterial genome. In addition to the well-documented reactivation of infectious ancient pathogens (bacteria, viruses, protozoa), we show now that global warming could contribute to the emergence of new antibiotic resistances through the mobilization by contemporary bacteria of ancient DNA released from thawing permafrost.FundingCNRS PRC research grant (PRC1484-2018) to C.A. E C-F was supported by a PhD grant (DGA/DS/MRIS) #2017 60 0004. GG and JS were funded by ERC PETA-CARB (#338335) and the HGF Impulse and Networking Fund (ERC-0013).

Serratia marcescens is a frequent cause of health care-associated infections and has led to multiple outbreaks. Here, we report the draft genome of a multidrug-resistant S. marcescens strain 189 which was isolated in 2012 as a predominant clone in a neonatal hospital in Kemerovo.