Background: The Arctic and Antarctic are the two most geographically distant bioregions on earth. Recent sampling efforts and following metagenomics have shed light on the global ocean microbial diversity and function, yet the microbiota of polar regions has not been included in such global analyses.Results: Here a metagenomic study of seawater samples (n= 60) collected from different depths at 28 locations in the Arctic and Antarctic zones was performed, together with metagenomes from theTaraOceans. More than 7500 (19%) polar seawater-derived operational taxonomic units could not be identified in theTaraOceans datasets, and more than 3,900,000 protein-coding gene orthologs had no hits in the Ocean Microbial Reference Gene Catalog. Analysis of 214 metagenome assembled genomes (MAGs) recovered from the polar seawater microbiomes, revealed strains that are prevalent in the polar regions while nearly undetectable in temperate seawater. Metabolic pathway reconstruction for these microbes suggested versatility for saccharide and lipids biosynthesis, nitrate and sulfate reduction, and CO₂fixation. Comparison between the Arctic and Antarctic microbiomes revealed that antibiotic resistance genes were enriched in the Arctic while functions like DNA recombination were enriched in the Antarctic.Conclusions: Our data highlight the occurrence of dominant and locally enriched microbes in the Arctic and Antarctic seawater with unique functional traits for environmental adaption, and provide a foundation for analyzing the global ocean microbiome in a more complete perspective.

The Scaly-foot Snail,Chrysomallon squamiferum, presents a combination of biomineralised features, reminiscent of enigmatic early fossil taxa with complex shells and sclerites such as sachtids, but in a recently-diverged living species which even has iron-infused hard parts. Thus the Scaly-foot Snail is an ideal model to study the genomic mechanisms underlying the evolutionary diversification of biomineralised armour. Here, we present a high-quality whole-genome assembly and tissue-specific transcriptomic data, and show that scale and shell formation in the Scaly-foot Snail employ independent subsets of 25 highly-expressed transcription factors. Comparisons with other lophotrochozoan genomes imply that this biomineralisation toolkit is ancient, though expression patterns differ across major lineages. We suggest that the ability of lophotrochozoan lineages to generate a wide range of hard parts, exemplified by the remarkable morphological disparity in Mollusca, draws on a capacity for dynamic modification of the expression and positioning of toolkit elements across the genome.

Thiosulfate oxidation by microbes has a major impact on global sulfur cycling. Here, we provide evidence that bacteria within variousRoseobacterlineages are important for thiosulfate oxidation in marine biofilms. We isolate and sequence the genomes of 54 biofilm-associatedRoseobacterstrains, finding conservedsoxgene clusters for thiosulfate oxidation and plasmids, pointing to a niche-specific lifestyle. Analysis of global ocean metagenomic data suggests thatRoseobacterstrains are abundant in biofilms and mats on various substrates, including stones, artificial surfaces, plant roots, and hydrothermal vent chimneys. Metatranscriptomic analysis indicates that the majority of activesoxgenes in biofilms belong toRoseobacterstrains. Furthermore, we show thatRoseobacterstrains can grow and oxidize thiosulfate to sulfate under both aerobic and anaerobic conditions. Transcriptomic and membrane proteomic analyses of biofilms formed by a representative strain indicate that thiosulfate inducessoxgene expression and alterations in cell membrane protein composition, and promotes biofilm formation and anaerobic respiration. We propose that bacteria of theRoseobactergroup are major thiosulfate-oxidizers in marine biofilms, where anaerobic thiosulfate metabolism is preferred.

Post-translational modification (PTM) of proteins is one important strategy employed by bacteria for environmental adaptation. However, PTM profiles in deep-sea microbes remain largely unexplored. We provide here insight into PTMs in a hydrothermal vent microbial community through integration of metagenomics and metaproteomics. In total, 2919 unique proteins and 1306 unique PTMs were identified, whereas the latter included acetylation, deamination, hydroxylation, methylation, nitrosylation, oxidation, and phosphorylation. These modifications were unevenly distributed among microbial taxonomic and functional categories. A connection between modification types and particular functions was demonstrated. Interestingly, PTMs differed among the orthologous proteins derived from different bacterial groups. Furthermore, proteomic mapping to the draft genome of a Nitrospirae bacterium revealed novel modifications for proteins that participate in energy metabolism, signal transduction, and inorganic ion transport. Our results suggest that PTMs are enriched in specific functions, which would be important for microbial adaptation to extreme conditions of the hydrothermal vent. PTMs in deep-sea are highly diverse and divergent, and much broader investigations are needed to obtain a better understanding of their functional roles.

The taxonomic structure of biofilms on 0.3-mm microplastics differed significantly from that on 3-mm microplastics or glass particles. Compared with the 3-mm microplastics, biofilms on 0.3-mm microplastics were enriched for genes involved in flagellar-based motility and chemotaxis, pointing to a more 'mobile' community. The association between motility and bacterial colonization of 0.3-mm microplastics was observed through laboratory experiments using isolated strains.

Accumulation of trimethylamine N -oxide improves both growth and survival of deep-sea bacteria under high hydrostatic pressure.