Sobolev, A. | bioRxiv Science

bioRxiv2026

Water-mass origin and transformation shapes seawater microbiomes in the northeastern Barents Sea and the St. Anna Trough

The St. Anna Trough region is a key Eurasian Arctic gateway connecting the northeastern Barents Sea, northern Kara Sea, and central Arctic Ocean. The region is characterized by complex hydrodynamics, with multiple water masses of local and Atlantic origin interacting and undergoing transformation. In this study, we investigated whether seawater microbiome composition correlates with water-mass origin and can be used to help delineate water masses. We collected 115 seawater samples representing major regional water masses - Arctic surface water, meltwater, cold dense water, Barents Sea branch water, the recently discovered Keldysh Current water, and mixed waters - and analyzed them using 16S rRNA gene amplicon sequencing. We found that microbiome composition closely followed water mass structure, which, together with thermohaline properties and depth, explained the majority (61.2%) of microbiome composition variation. Distinct microbial patterns were associated with Atlantic and Arctic water masses, except for the Arctic surface water, which lacked a distinct microbiome and resembled those of meltwater or the Keldysh Current microbiomes. Differential abundance and network analyses revealed characteristic bacterial markers: SAR11 (Clades Ia and IV), Roseibacillus, SV1-3 (Microbacteriaceae), SAR86 clade, and AEGEAN-169 marine group in the Keldysh Current; Halieaceae, Planktomarina, NS5 marine group, and Sulfitobacter in meltwater; SUP05 cluster, SAR86, SAR92, and SAR324 clade in cold dense water; Nitrincolaceae and Amylibacter in Barents Sea branch water; Flavobacteriaceae and Chitinophagales in mixed waters. These differences were driven primarily by shifts in relative abundance of widespread Arctic bacterial taxa rather than by differential prevalence of bacterial groups. Our results demonstrate that seawater microbiomes can serve as sensitive biological tracers of water mass origin and transformation in the Eurasian Arctic. Furthermore, the distinct Keldysh Current microbiome supports its recognition as a novel hydrographic feature and indicates its role as a biological corridor transporting Atlantic-associated biota eastward toward the Kara Sea. These findings suggest that "Atlantification" of Eurasian Arctic includes a microbial component, highlighting marine microbiomes as indicators of ongoing ecological changes in the Arctic Ocean.

microbiology↗

bioRxiv2021

3C-seq-captured chromosome conformation of the hyperthermophilic archaeon Thermofilum adornatum

Three-dimensional structure of chromosomes displays diverse patterns across the tree of life, with compartments, interaction domains and loops being quite universally observed. The archaeal kingdom remains understudied to this extent so far, despite representing an interesting area from evolutionary and other perspectives. Here we describe the spatial chromosomal organization of a hyperthermophilic crenarchaeon Thermofilum adornatum strain 1910b based on high-throughput chromosome conformation capture (3C-seq) approach. The chromosome contact map showed a curved secondary diagonal almost orthogonal to the main one. No evidence of chromosome loops was present. We were able to identify boundaries of different strengths between chromosome interaction domains (CIDs) albeit moderate. The plaid-like patterns previously reported for Sulfolobus archaea were not observed. However, the calculation of A/B compartments divided the genome into 2 domains that were different by the density of predicted highly expressed genes and location of origins. Further comparison of these domains with whole-genome gene expression profiles will allow to test whether these domains represent expression-associated compartments. If so, it is possible that they represent primitive compartments evolutionarily older than the plaid patterns of Sulfolobus and higher eukaryotes. Further exploration of 3D chromatin in all branches of archaeal diversity will elucidate the evolution of the links between structural and functional organization in live organisms.

bioinformatics↗