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1. Genomic diversity and adaptation in Arctic marine bacteria

   https://doi.org/10.1128/mbio.01555-25  

   Sadler, Michael C; Wietz, Matthias; Mino, Sayaka; Morris, Robert M (September 2025, mBio)

   Giovannoni, Stephen J (Ed.)

   ABSTRACT Arctic marine bacteria experience seasonal changes in temperature, salinity, light, and sea ice cover. Time-series and metagenomic studies have identified spatiotemporal patterns in Arctic microbial communities, but a lack of complete genomes has limited efforts to identify the extent of genomic diversity in Arctic populations. We cultured and sequenced the complete genomes of 34 Arctic marine bacteria to identify patterns of gene gain, loss, and rearrangement that structure genomes and underlie adaptations to Arctic conditions. We found that the most abundant lineage in the Arctic (SAR11) is comprised of diverse species and subspecies, each encoding 50–150 unique genes. Half of the 16 SAR11 genomes harbor a genomic island with the potential to enhance survival in the Arctic by utilizing the osmoprotectant and potential methyl donor glycine betaine. We also cultured and sequenced four species representing an uncultured family ofPseudomonadales, four subspecies ofPseudothioglobus(SUP05), a genus of high GCPuniceispirillales(SAR116), and a family of low GC SAR116. Time-series 16S rRNA amplicon data indicate that this culture collection represents up to 60% of the marine bacterial community in Arctic waters. Their genomes provide insights into the evolutionary processes that underlie bacterial diversity and adaptation to Arctic waters.IMPORTANCEGenetic diversity has limited efforts to assemble and compare whole genomes from natural populations of marine bacteria. We developed a cultivation-based population genomics approach to culture and sequence the complete genomes of bacteria from the Arctic Ocean. Cultures and closed genomes obtained in this study represent previously uncultured families, genera, and species from the most abundant lineages of bacteria in the Arctic. We report patterns of gene gain, loss, rearrangement, and adaptation in the dominant lineage (SAR11), as well as the size, composition, and structure of genomes from several other groups of marine bacteria. This work demonstrates the potential for cultivation-based high-throughput genomics to enhance understanding of the processes underlying genomic diversity and adaptation. 

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2. Complete genome sequences of 34 Arctic marine bacteria

   https://doi.org/10.1128/mra.00158-25  

   Sadler, Michael C; Mino, Sayaka; Morris, Robert M (October 2025, Microbiology Resource Announcements)

   Becket, Elinne (Ed.)

   ABSTRACT We report the complete genome sequences of 34 Arctic marine bacteria, including 16Pelagibacter(SAR11), 4Pseudothioglobus(SUP05), 2 SAR116, and 4Njordibacter. These cultures and closed genomes enhance the understanding of microbial diversity in the Arctic and the evolutionary processes underlying adaptation. 

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3. Pseudoalteromonas is a symbiont of marine invertebrates that exhibits broad patterns of phylosymbiosis

   https://doi.org/10.1093/ismejo/wrag091  

   De_Santiago, Alejandro; Barnes, Shelby; Pereira, Tiago José; Marcellino-Barros, Mirayana; Durden, Lekeah; Han, Min Khant; Thrash, J Cameron; Bik, Holly M (April 2026, The ISME Journal)

   Abstract Despite growing insights into the composition of marine invertebrate microbiomes, our understanding of their ecological and evolutionary patterns remains poor, owing to limited sampling depth and low-resolution datasets. Previous studies have provided conflicting results that both confirm and deny the existence of phylosymbiosis between marine invertebrates and marine bacteria. Here, we investigated potential animal-microbe symbioses in Pseudoalteromonas, a bacterial genus consistently identified as a core microbiome taxon in diverse invertebrates. Using a pangenomic analysis of 236 free-living and invertebrate-associated bacterial strains (including two new nematode-associated isolates generated in this study), we confirm that Pseudoalteromonas is a symbiont with substantial evidence of phylosymbiosis across at least three marine invertebrate phyla (e.g., Nematoda, Mollusca, and Cnidaria). Patterns of symbiosis were consistent irrespective of geography (including in Antarctica), with FISH images from nematodes indicating that bacterial symbionts form biofilms in the mouth and esophagus and are sometimes present in female nematode ovaries exhibiting stunted development. The evolutionary history of Pseudoalteromonas is marked by substantial host-switching and lifestyle transitions, and host-associated genomes suggest that these bacteria are facultative symbionts involved in nutritional symbioses. In marine environments, we hypothesize that horizontally acquired symbionts may have co-evolved with invertebrates, using host mucus as a physical niche and food source, while providing their animal hosts with Vitamin B, amino acids, and bioavailable carbon compounds in return. 

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4. Polymer degrading marine Microbulbifer bacteria: an un(der)utilized source of chemical and biocatalytic novelty

   https://doi.org/10.3762/bjoc.20.146  

   Zhong, Weimao; Agarwal, Vinayak (January 2024, Beilstein Journal of Organic Chemistry)

   Microbulbiferis a genus of halophilic bacteria that are commonly detected in the commensal marine microbiomes. These bacteria have been recognized for their ability to degrade polysaccharides and other polymeric materials. Increasingly,Microbulbifergenomes indicate these bacteria to be an untapped reservoir for novel natural product discovery and biosynthetic novelty. In this review, we summarize the distribution ofMicrobulbiferbacteria, activities of the various polymer degrading enzymes that these bacteria produce, and an up-to-date summary of the natural products that have been isolated fromMicrobulbiferstrains. We argue that these bacteria have been hiding in plain sight, and contemporary efforts into their genome and metabolome mining are going to lead to a proliferation ofMicrobulbifer-derived natural products in the future. We also describe, where possible, the ecological interactions of these bacteria in marine microbiomes. 

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5. A genomic resource for exploring bacterial-viral dynamics in seagrass ecosystems

   https://doi.org/10.1101/2024.12.06.627215  

   Ettinger, Cassandra L; Stajich, Jason E (December 2024, bioRxiv)

   Abstract BackgroundSeagrasses are globally distributed marine flowering plants that play foundational roles in coastal environments as ecosystem engineers. While research efforts have explored various aspects of seagrass-associated microbial communities, including describing the diversity of bacteria, fungi and microbial eukaryotes, little is known about viral diversity in these communities. ResultsTo begin to address this, we leveraged metagenomic sequencing data to generate a catalog of bacterial metagenome-assembled genomes (MAGs) and phage genomes from the leaves of the seagrass,Zostera marina. We expanded the robustness of this viral catalog by incorporating publicly available metagenomic data from seagrass ecosystems. The final MAG set represents 85 high-quality draft and 62 medium-quality draft bacterial genomes. While the viral catalog represents 354 medium-quality, high-quality, and complete viral genomes. Predicted auxiliary metabolic genes in the final viral catalog had putative annotations largely related to carbon utilization, suggesting a possible role for phage in carbon cycling in seagrass ecosystems. ConclusionsThese genomic resources provide initial insight into bacterial-viral interactions in seagrass meadows and are a foundation on which to further explore these critical interkingdom interactions. These catalogs highlight a possible role for viruses in carbon cycling in seagrass beds which may have important implications for blue carbon management and climate change mitigation. 

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