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

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 mixed results when evaluating patterns of phylosymbiosis between marine invertebrates and marine bacteria. Here, we investigated potential animal-microbe symbioses in Pseudoalteromonas, an overlooked 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 novel 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. 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 mutualisms. 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.

Marine Invertebrates

Novelty, diversity, and genetic dark matter in enterococci of invertebrates.

Enterococci appear to have originated in the guts of early terrestrializing arthropods and invertebrates over 425 million years ago-hosts that are now highly diverse and widespread in nature today. Yet most knowledge of the genus comes from human infection-associated lineages with genomes swollen by the recent accretion of foreign DNA conveyed by mobile elements. Because invertebrates dominate terrestrial animal diversity and biomass, they would be predicted to constitute a major but little-explored reservoir of enterococcal diversity. We therefore systematically examined Enterococcus association and species diversification in invertebrate hosts of the comparatively natural, isolated, but well-characterized environment of the Azorean island of Terceira. Over 100 invertebrate specimens were examined for associated enterococci, which were taxonomically classified by whole-genome sequencing. Supporting the existence of a large pool of uncharacterized enterococci and Enterococcus-adapted genes, 40% (eight of 20) of the Enterococcus species identified were either undescribed, including four candidate new species described here, or very recently discovered. In contrast, control isolates from vertebrates were exclusively of known species typical of sampling elsewhere, discounting geographic isolation as a main driver of the novelty observed. Further, because of the abundance of E. casseliflavus and E. flavescens in this collection, we obtained the resolution necessary to quantify the divergence and decipher the drivers of speciation in the controversial division between these naturally vancomycin-resistant species. These findings provide robust support for the existence of a large pool of new species and unexplored adaptive traits in invertebrate-associated enterococci-diverse environmental survival traits optimized for expression in an enterococcal background, and well positioned for transmission into human-associated enterococcal strains.IMPORTANCEEnterococci are auxotrophic gut-associated bacteria that co-evolved with their terrestrial hosts over many eons. In the last 75 years-the "antibiotic era"-E. faecalis and E. faecium gained genes for antibiotic resistance and enhanced virulence, emerging as leading causes of multidrug-resistant infection. Little is known about the source of those genes or the pathway by which they entered human-associated strains. A recent global survey suggested a potentially large repository of uncharacterized genetic diversity in the enterococci of invertebrates. We directly tested this prospect by examining enterococci of invertebrate hosts in a largely natural and pastoral environment. Our findings provide clear evidence that invertebrates naturally harbor vast unexplored enterococcal diversity. Moreover, associations are likely driven by intrinsic host selection factors rather than geographic isolation. This expands our knowledge of Enterococcus biodiversity, including the identification of four novel species, identifying a vast reservoir of enterococcal genes available to species that colonize and infect humans.

Animals

The effects of cold temperature on the development, microbiome, and transcriptome of the sea anemone Nematostella vectensis.

Thermal conditions impact essentially all aspects of the physiology for ectotherms. While the effects of high temperatures have been widely studied, cold temperature effects on aquatic invertebrates and their microbial communities have been poorly characterized. To determine the diverse effects of exposure to cold temperatures, we assessed acute and long-term impacts of ecologically relevant low temperatures on the development, microbiome, and gene expression of the sea anemone Nematostella vectensis. Two hours post fertilization, embryos were exposed to temperatures from 4°C to 35°C and development rate to the juvenile stage was quantified. We found temperature impacts the development rate of embryos, where lower temperatures extended development time and resulted in mortality below 10°C. For both microbiome and host transcriptomic responses, anemones were held at 20°C, 10°C, and 0°C and compared at 24 hours and 7 days. Extended exposures to colder temperatures caused restructuring of the host-associated microbiome, with the loss of common taxonomic groups from the class Bacteroidia and Bacilli. Lastly, cold stress induced significant changes in gene expression, which were more pronounced at the 10°C than 0°C but showed little change over time in each temperature. Interestingly, expression of genes associated with innate immunity were among the most differentially expressed genes including heat shock proteins and innate immune genes providing a potential host-imposed mechanism to explain the shift in the microbiome. Overall, cold temperatures have broad effects on many facets of this sea anemone and its microbial community and indicate the importance of cold temperature events when characterizing how ectotherms acclimate to thermal variation.

Animals

Discovery, biosynthesis, and bioactivities of peptidic natural products from marine sponges and sponge-associated bacteria.

Covering 2010 to 2025Sponges are benthic, sessile invertebrate metazoans that are some of the most prolific sources of natural products in the marine environment. Sponge-derived natural products are often endowed with favorable pharmaceutical bioactivities, and paired with their structural complexity, have long served as title compounds for chemical syntheses. Sponges are holobionts, in that the sponge host is associated with symbiotic and commensal microbiome. Natural products isolated from sponges can be produced by the sponge host, or the associated microbiome. Recent genomic studies have shed light on the sponge eukaryotic host as the true producer of several classes of sponge-derived peptidic natural products. In this review spanning years 2010-2025, we describe peptidic natural products isolated from the sponge hosts and the associated microbiome, detail their biosynthetic processes where known, and offer forward looking insights into future innovation in discovery and biosynthesis of peptidic natural products from marine sponges.

Porifera

Native edaphoclimatic regions shape soil communities of crop wild progenitors.

Unveiling the soil biological communities ecologically associated with crop wild progenitors (CWPs) in their habitats of origin is essential for advancing productive and sustainable agriculture. A field survey was conducted to investigate the edaphoclimatic conditions and soil bacterial, fungal, protist, and invertebrate communities of 125 populations of direct progenitors of major crops for world agriculture. The wild populations clustered into four ecoregions shaped by two edaphoclimatic dimensions: one summarizing variations in soil sand contents and nutrients concentrations, and the other featuring changes in aridity, soil pH, and carbon storage potential. We identified a common soil core community across CWPs that varied significantly along deserts to tropical seasonal forests and savannas. The assembly of the soil core community was driven by varying environmental preferences amongst soil biodiversity kingdoms, reflecting potential shifts in their functional profiles. The tropical ecoregion exhibited higher proportion of acidophilic bacteria, fungal, and protist parasites, whilst desert ecosystems harboured greater abundances of saprophytic fungi and heterotrophic protists. Moreover, CWPs displayed unique microhabitats that incorporate variability into the soil community assembly. Our work reveals the biogeography of soil communities associated with CWPs, the first step towards the development of microbial rewilding initiatives.

centres of origin