Microbiome of the freshwater sponge Ephydatia muelleri shares compositional and functional similarities with those of marine sponges

Microbiome and pollutants in the freshwater sponges Ephydatia muelleri (Lieberkühn, 1856) and Spongilla lacustris (Linnaeus, 1758) from the sub-Arctic Pasvik river (Northern Fennoscandia)

Despite the ecosystem functions offered by sponges in freshwater habitats, fragmentary studies have targeted their microbiome and the bioaccumulation of legacy and emerging organic micropollutants, making it difficult to test hypotheses about sponge-microbe specificity and response to environmental factors and stressors. The sponge species Ephydatia muelleri and Spongilla lacustris, coexisting in two sites of the Pasvik River (northern Fennoscandia), were analyzed for persistent organic pollutant (POPs) and chemicals of emerging concern (CECs), along with quali-quantitative microbiological features. River water and sediment were similarly treated to establish if the obtained data were site- or sponge-specific. CECs mainly occurred in abiotic matrices, with trimethoprim and ciprofloxacin prevailing in water and sediment, respectively. Only ciprofloxacin and diclofenac were detected in sponges, with higher concentrations generally determined in S. lacustris than E. muelleri. Overall, POP concentrations were in the order polycyclic aromatic hydrocarbons > chlorobenzenes > polychlorobiphenyls > polychloronaphthalenes, with higher values in sponges with respect to abiotic matrices. Generally, POPs occurred at higher concentrations in S. lacustris than E. muelleri. Enzyme activity measurements displayed diverse trends across samples and sites, with E. muelleri displaying higher glycolytic activity than S. lacustris. Prokaryotic abundance in sponges generally exceeded that found in abiotic matrices. Proteobacteria, Planctomycetota, Actinobacteriota, Verrucomicrobiota, and Cyanobacteria predominated in sponge samples, with slight differences between sponge species and sampling sites, whereas Desulfobacterota and Acidobacterota were retrieved mostly in sediment samples. The sponge-associated bacterial communities appeared to be differently affected by pollutant concentration at the site level. Overall, this study highlights the ecological role of freshwater sponges, shedding light on their microbial associations, pollutant bioaccumulation, and potential as bioindicators of aquatic ecosystem health. The findings emphasize the importance of considering both microbial diversity and contaminant accumulation for a holistic understanding of the roles played by freshwater sponges in human-impacted environments.

From Sea to Freshwater: Shared and Unique Microbial Traits in Sponge Associated Prokaryotic Communities

Despite their ecological significance and biotechnological potential, freshwater sponges remain relatively understudied compared to their marine counterparts. In special, the prokaryotic communities of species from isolated yet highly diverse ecosystems, such as the Amazon Rainforest, remain unknown, leaving an important part of the Porifera microbiome underexplored. Using high-throughput sequencing of the 16S rRNA gene, we unraveled the structure of the microbiota associated to the freshwater sponges Heteromeyenia cristalina and Metania reticulata for the first time. Their microbiome was compared with that of the haplosclerid marine sponges Amphimedon viridis and Haliclona melana; and the tetractinellid Cinachyrella alloclada. Our findings reveal not only a shared core microbiome between the freshwater and marine environments but also indicate functional redundancy in their communities, suggesting that certain microbial metabolic functions are conserved across diverse habitats. Comparisons between ecosystems also revealed that microbiomes of freshwater sponges can be richer and more diverse than those of marine species. Moreover, we compared the microbiome of adults and asexual reproduction structures (buds and gemmules) of sponges from both habitats, revealing a remarkable similarity between adults and their respective offsprings, indicating an important role of vertical transmission in this mode of reproduction. Our observations emphasize the dynamic interactions and the adaptability of the sponge-associated microbiota, providing insights into how these symbiotic associations were affected during the colonization of freshwater environments and shedding light into how symbiotic relationships are maintained throughout generations.

Freshwater sponges in the southeastern U.S. harbor unique microbiomes that are influenced by host and environmental factors

Marine, and more recently, freshwater sponges are known to harbor unique microbial symbiotic communities relative to the surrounding water; however, our understanding of the microbial ecology and diversity of freshwater sponges is vastly limited compared to those of marine sponges. Here we analyzed the microbiomes of three freshwater sponge species: Radiospongilla crateriformis, Eunapius fragilis, and Trochospongilla horrida, across four sites in western North Carolina, U.S.A. Our results support recent work indicating that freshwater sponges indeed harbor a distinct microbiome composition compared to the surrounding water and that these varied across sampling site indicating both environmental and host factors in shaping this distinct community. We also sampled sponges at one site over 3 months and observed that divergence in the microbial community between sponge and water occurs at least several weeks after sponges emerge for the growing season and that sponges maintain a distinct community from the water as the sponge tissue degrades. Bacterial taxa within the Gammproteobacteria, Alphproteobacteria, Bacteroidota (Flavobacteriia in particular), and Verrucomicrobia, were notable as enriched in the sponge relative to the surrounding water across sponge individuals with diverging microbial communities from the water. These results add novel information on the assembly and maintenance of microbial communities in an ancient metazoan host and is one of few published studies on freshwater sponge microbial symbiont communities.

Dynamics, diversity, and roles of bacterial transmission modes during the first asexual life stages of the freshwater sponge Spongilla lacustris

BACKGROUND

Sponge-associated bacteria play important roles in the physiology of their host, whose recruitment processes are crucial to maintain symbiotic associations. However, the acquisition of bacterial communities within freshwater sponges is still under explored. Spongilla lacustris is a model sponge widely distributed in European rivers and lakes, producing dormant cysts (named gemmules) for their asexual reproduction, before winter. Through an in vitro experiment, this study aims to describe the dynamics of bacterial communities and their transmission modes following the hatching of these gemmules.

RESULTS

An overall change of bacterial β-diversity was observed through the ontology of the juvenile sponges. These temporal differences were potentially linked, first to the osculum acquisition and the development of a canal system, and then, the increasing colonization of the Chlorella-like photosymbionts. Gemmules hatching with a sterilized surface were found to have a more dispersed and less diverse microbiome, revealing the importance of gemmule epibacteria for the whole holobiont stability. These epibacteria were suggested to be vertically transmitted from the maternal tissues to the gemmule surface. Vertical transmission through the incorporation of bacterial communities inside of the gemmule, was also found as a dominant transmission mode, especially with the nitrogen fixers Terasakiellaceae. Finally, we showed that almost no ASVs were shared between the free-living community and the juveniles, suggesting that horizontal recruitment is unlikely to happen during the first stages of development. However, the free-living bacteria filtered are probably used as a source of nutrients, allowing an enrichment of copiotrophic bacteria already present within its microbiome.

CONCLUSIONS

This study brings new insight for a better understanding of the microbiome acquisition during the first stages of freshwater sponge development. We showed the importance of epibacterial communities on gemmules for the whole holobiont stability, and demonstrated the near absence of recruitment of free-living bacteria during the first stages.

Evidence for transporter-mediated uptake of environmental L-glutamate in a freshwater sponge, Ephydatia muelleri

The freshwater sponge, Ephydatia muelleri, lacks a nervous or endocrine system and yet it exhibits a coordinated whole-body action known as a "sneeze" that can be triggered by exposure to L-glutamate. It is not known how L-glutamate is obtained by E. muelleri in sufficient quantities (i.e., 70 µM) to mediate this response endogenously. The present study tested the hypothesis that L-glutamate can be directly acquired from the environment across the body surface of E. muelleri. We demonstrate carrier mediated uptake of two distinct saturable systems with maximal transport rates (Jmax) of 64.27 ± 4.98 and 25.12 ± 1.87 pmols mg-1 min-1, respectively. The latter system has a higher calculated substrate affinity (Km) of 2.87 ± 0.38 µM compared to the former (8.75 ± 1.00 µM), indicative of distinct systems that can acquire L-glutamate at variable environmental concentrations. Further characterization revealed potential shared pathways of L-glutamate uptake with other negatively charged amino acids, namely D-glutamate and L-aspartate, as well as the neutral amino acid L-alanine. We demonstrate that L-glutamate uptake does not appear to rely on exogenous sodium or proton concentrations as removal of these ions from the bathing media did not significantly alter uptake. Likewise, L-glutamate uptake does not seem to rely on internal proton motive forces driven by VHA as application of 100 nM of the VHA inhibitor bafilomycin did not alter uptake rates within E. muelleri tissues. Whether the acquired amino acid is used to supplement feeding or is stored and accumulated to mediate the sneeze response remains to be determined.

Divergent bacterial landscapes: unraveling geographically driven microbiomes in Atlantic cod

Establishing microbiome signatures is now recognized as a critical step toward identifying genetic and environmental factors shaping animal-associated microbiomes and informing the health status of a given host. In the present work, we prospectively collected 63 blood samples of the Atlantic cod population of the Southern Gulf of Saint Lawrence (GSL) and characterized their 16S rRNA circulating microbiome signature. Our results revealed that the blood microbiome signature was dominated at the phylum level by Proteobacteria, Bacteroidetes, Acidobacteria and Actinobacteria, a typical signature for fish populations inhabiting the GSL and other marine ecosystems. At the genus level, however, we identified two distinct cod groups. While the microbiome signature of the first group was dominated by Pseudoalteromonas, a genus we previously found in the microbiome signature of Greenland and Atlantic halibut populations of the GSL, the second group had a microbiome signature dominated by Nitrobacter and Sediminibacterium (approximately 75% of the circulating microbiome). Cods harboring a Nitrobacter/Sediminibacterium-rich microbiome signature were localized in the most southern part of the GSL, just along the northern coast of Cape Breton Island. Atlantic cod microbiome signatures did not correlate with the weight, length, relative condition, depth, temperature, sex, and salinity, as previously observed in the halibut populations. Our study provides, for the first time, a unique snapshot of the circulating microbiome signature of Atlantic cod populations and the potential existence of dysbiotic signatures associated with the geographical distribution of the population, probably linked with the presence of nitrite in the environment.

Metagenomic insights into jellyfish-associated microbiome dynamics during strobilation

Host-associated microbiomes can play key roles in the metamorphosis of animals. Most scyphozoan jellyfish undergo strobilation in their life cycles, similar to metamorphosis in classic bilaterians. The exploration of jellyfish microbiomes may elucidate the ancestral mechanisms and evolutionary trajectories of metazoan-microbe associations and interactions during metamorphosis. However, current knowledge of the functional features of jellyfish microbiomes remains limited. Here, we performed a genome-centric analysis of associated microbiota across four successive life stages (polyp, early strobila, advanced strobila, and ephyra) during strobilation in the common jellyfish Aurelia coerulea. We observed shifts in taxonomic and functional diversity of microbiomes across distinct stages and proposed that the low microbial diversity in ephyra stage may be correlated with the high expression of the host-derived antimicrobial peptide aurelin. Furthermore, we recovered 43 high-quality metagenome-assembled genomes and determined the nutritional potential of the dominant Vibrio members. Interestingly, we observed increased abundances of genes related to the biosynthesis of amino acids, vitamins, and cofactors, as well as carbon fixation during the loss of host feeding ability, indicating the functional potential of Aurelia-associated microbiota to support the synthesis of essential nutrients. We also identified several potential mechanisms by which jellyfish-associated microbes establish stage-specific community structures and maintain stable colonization in dynamic host environments, including eukaryotic-like protein production, bacterial secretion systems, restriction-modification systems, and clustered regularly interspaced short palindromic repeats-Cas systems. Our study characterizes unique taxonomic and functional changes in jellyfish microbiomes during strobilation and provides foundations for uncovering the ancestral mechanism of host-microbe interactions during metamorphosis.

Animal Microbiomes as a Source of Novel Antibiotic-Producing Strains

Natural compounds continue to serve as the most fruitful source of new antimicrobials. Analysis of bacterial genomes have revealed that the biosynthetic potential of antibiotic producers by far exceeds the number of already discovered structures. However, due to the repeated discovery of known substances, it has become necessary to change both approaches to the search for antibiotics and the sources of producer strains. The pressure of natural selection and the diversity of interactions in symbiotic communities make animal microbiomes promising sources of novel substances. Here, microorganisms associated with various animals were examined in terms of their antimicrobial agents. The application of alternative cultivation techniques, ultrahigh-throughput screening, and genomic analysis facilitated the investigation of compounds produced by unique representatives of the animal microbiota. We believe that new strategies of antipathogen defense will be discovered by precisely studying cell-cell and host-microbe interactions in microbiomes in the wild.

Freshwater Sponges as a Neglected Reservoir of Bacterial Biodiversity

Freshwater sponges (Spongillida: Demospongiae), including more than 240 described species, are globally distributed in continental waters (except for Antarctica), where they cover both natural and artificial surfaces. However, fragmentary studies have targeted their microbiome, making it difficult to test hypotheses about sponge-microbe specificity and metabolic relationships, along with the environmental factors playing key roles in structuring the associated microbial communities. To date, particular attention has been paid to sponges (family Lubomirskiidae) that are endemic to Lake Baikal. Few other freshwater sponge species (e.g., Ephydatia spp., Eunapius spp., and Spongilla lacustris), from lakes and rivers spanning from Europe to South and North America, have been targeted for microbiological studies. Representatives of the phyla Proteobacteria, Bacteroidetes, and Actinobacteria largely predominated, and high differences were reported between the microbiome of freshwater and marine sponges. Several bacterial strains isolated from freshwater sponges can produce bioactive compounds, mainly showing antibiotic activities, with potential application in biotechnology. Understanding the roles played by sponge microbiomes in freshwater ecosystems is still in its infancy and has yet to be clarified to disentangle the ecological and evolutionary significance of these largely under-investigated microbial communities. This review was aimed at providing the main available information on the composition and biotechnological potential of prokaryotic communities associated with healthy freshwater sponges, as a neglected component of the global sponge microbiome, to stimulate researchers interested in the field.