In situ pumping activity of the sponge Aplysina aerophoba, Nardo 1886

Aplysina aerophoba, Nardo 1886 is a common and well examined demosponge in the Mediterranean Sea. For sponges, as sessile, inner filter feeders, the most important function is pumping water through their canal system. This flow through is actively generated, supplies the sponge with oxygen and food particles and washes out waste products. Oxygen measurements ex situ, as a given example, show high oxygen saturations inside pumping sponges and oxygen depletion in non-pumping sponges. Thus, the oxygen situation within the sponge, like the food particle supply, waste washout and others, are directly related to its active pumping. To learn more about the poriferan function, it is important to know more about its undisturbed in situ pumping activity and consequently about the correlated conditions inside the sponge body.We conducted a tracer experiment in situ and tested sponge activity in terms of active pumping. Our technique excluded stress and disturbance to the sponges, hence minimizing experimental artefacts. The results show Aplysina aerophoba to be permanently pumping, which is implying a permanent supply of oxygen and of course food particles as well as a permanent washout of waste products and a permanent, presumably high energy consumption.We therefore conclude, that Aplysina aerophoba is always well supplied with oxygen, and that tissue anoxia or anaerobic metabolisms are of no significant importance in this sponge species. This fact of a permanent flow through in sponges will have to be taken into account for past and future hypotheses on the physiology of the sponge-microbial systems.     

Sponges (Porifera) and eukaryotic, unicellular plankton: A case study on Aplysina aerophoba, Nardo 1886 in the Northern Adriatic

Sponges (Porifera), in general, are pumping water through their bodies. This water contains planktonic eukaryotic and procaryotic organisms as well as particulate and dissolved organic matter as potential food source. We analyzed the eukaryotic unicellular plankton fraction from water surrounding sponges of the species Aplysina aerophoba, Nardo 1886, from sponge tissue, as well as from water expelled from those sponges. We found sponges without any remnants of plankton in their tissue, as well as specimens which incorporated high numbers of remnants of organisms after planktonic “blooms”. In laboratory experiments, sponges were not showing any uptake of plankton from their surrounding water. Sponges are generally considered as inner filter feeders. However, our results indicate that eukaryotic unicellular plankton organisms are not the main food resource of the common sponge A. aerophoba. This raises the question if filter feeding is actually the main characteristic of the poriferan lifestyle.     

Deep sequencing reveals diversity and community structure of complex microbiota in five Mediterranean sponges

Marine sponges harbor dense microbial communities of exceptionally high diversity. Despite the complexity of sponge microbiota, microbial communities in different sponges seem to be remarkably similar. In this study, we used a subset of a previously established 454 amplicon pyrosequencing dataset (Schmitt and Taylor, unpublished data). Five Mediterranean sponges were chosen including the model sponge Aplysina aerophoba to determine the extent of uniformity by defining (i) the core microbial community, consisting of bacteria found in all sponges, (ii) the variable microbial community, consisting of bacteria found in 2–4 sponges, and (iii) the species-specific community, consisting of bacteria found in only one sponge. Using the enormous sequencing depth of pyrosequencing the diversity in each of the five sponges was extended to up to 15 different bacterial phyla per sponge with Proteobacteria and Chloroflexi being most diverse in each of the five sponges. Similarity comparison of bacteria on phylum and phylotype level revealed most similar communities in A. aerophoba and A. cavernicola and the most dissimilar community in Pseudocorticium jarrei. A surprising minimal core bacterial community was found when distribution of 97% operational taxonomic units (OTUs) was analyzed. Core, variable, and species-specific communities were comprised of 2, 26, and 72% of all OTUs, respectively. This indicates that each sponge contains a large set of unique bacteria and shares only few bacteria with other sponges. However, host species-specific bacteria are probably still closely related to each other explaining the observed similarity among bacterial communities in sponges.     

Bacterial Uptake by the Marine Sponge <Emphasis Type="Italic">Aplysina aerophoba</Emphasis>

Sponges (Porifera) are filter feeders that take up microorganisms from seawater and digest them by phagocytosis. At the same time, many sponges are known to harbor massive consortia of symbiotic microorganisms, which are phylogenetically distinct from those in seawater, within the mesohyl matrix. In the present study, feeding experiments were performed to investigate whether phylogenetically different bacterial isolates, hereafter termed “food bacteria,” microbial seawater consortia, and sponge symbiont consortia are taken up and processed differently by the host sponge. Aplysina aerophoba retained high numbers of bacterial isolates and microbial seawater consortia with rates of up to 2.76 × 10⁶ bacteria (g sponge wet weight)^–1 h^–1, whereas the retention of sponge symbionts was lower by nearly two orders of magnitude [5.37 × 10⁴ bacteria (g sponge wet weight)⁻¹ h^–1]. In order to visualize the processing of a food bacterium within sponge tissues, the green fluorescent protein-labeled Vibrio strain MMW1, which had originally been isolated from A. aerophoba, was constructed. Incubation of this strain with A. aerophoba and subsequent visualization in tissue cryosections showed its presence in the choanocytes and/or endopinacocytes lining the canals but, unlike latex beads, not in deeper regions of the mesohyl, which suggests digestion of the bacteria upon contact with the host. Denaturing gradient gel electrophoresis (DGGE) was performed on the incubation seawater to monitor the changes in phylogenetic composition after incubation of the sponge with either seawater or sponge symbiont consortia. However, the DGGE experiment provided no evidence for selective processing of individual lineages by the host sponge. In conclusion, this study extends early studies by Wilkinson et al. (Proc R Soc London B 220:519–528, 1984) that sponges, here A. aerophoba, are able to differentiate between food bacteria and their own bacterial symbionts.     

Phylogenetic characterization and in situ detection of bacterial communities associated with seahorses (Hippocampus guttulatus) in captivity

Although there are several studies describing bacteria associated with marine fish, the bacterial composition associated with seahorses has not been extensively investigated since these studies have been restricted to the identification of bacterial pathogens. In this study, the phylogenetic affiliation of seahorse-associated bacteria was assessed by 16S rRNA gene sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rRNA analysis. Both methods revealed that Vibrionaceae was the dominant population in Artemia sp. (live prey) and intestinal content of the seahorses, while Rhodobacteraceae was dominant in water samples from the aquaculture system and cutaneous mucus of the seahorses. To our knowledge, this is the first time that bacterial communities associated with healthy seahorses in captivity have been described.     

Visualization of initial bacterial colonization on dentine and enamel in situ

Bacterial colonization of dentine is of high relevance in cariology, endodontology and periodontology. The aim of the present in situ study was to establish recent methods for visualization and quantification of initial bacterial adherence to dentine in comparison to enamel. For this purpose, bovine enamel and dentine slabs were fixed on buccal sites of individual upper jaw splints worn by 6 subjects for 30 min, 120 min and 360 min, respectively. Adherent bacteria on the slabs were visualized and quantified with DAPI-staining (4′,6-diamidino-2-phenylindole) and fluorescence in situ hybridization (FISH) of streptococci and eubacteria using the CLSM (confocal laser scanning microscopy) as well as an epifluorescence microscope. In addition, the number of colony forming units was quantified after desorption. Representative samples were processed for SEM (scanning electron microscopy) and TEM (transmission electron microscopy). All methods clearly indicated that a significantly higher number of bacteria adhered to dentine than to enamel. Furthermore, the amount of bacteria on the dentine increased with increasing oral exposure time, but remained rather constant on the enamel. The CLSM allowed visualization of bacteria in the dentinal tubules. Bacteria were found preferentially at the openings of the dentine tubules, but were distributed randomly on the enamel.In conclusion, the adopted methods are suitable for visualization and quantification of bacterial adhesion to dentine. Even the initial bacterial colonization of dentine is much more pronounced than bacterial adherence to the enamel.     

Single-cell genomics reveals the lifestyle of Poribacteria,a candidate phylum symbiotically associated with marine sponges

In this study, we present a single-cell genomics approach for the functional characterization of the candidate phylum Poribacteria, members of which are nearly exclusively found in marine sponges. The microbial consortia of the Mediterranean sponge Aplysina aerophoba were singularized by fluorescence-activated cell sorting, and individual microbial cells were subjected to phi29 polymerase-mediated ‘whole-genome amplification''. Pyrosequencing of a single amplified genome (SAG) derived from a member of the Poribacteria resulted in nearly 1.6 Mb of genomic information distributed among 554 contigs analyzed in this study. Approximately two-third of the poribacterial genome was sequenced. Our findings shed light on the functional properties and lifestyle of a possibly ancient bacterial symbiont of marine sponges. The Poribacteria are mixotrophic bacteria with autotrophic CO₂-fixation capacities through the Wood–Ljungdahl pathway. The cell wall is of Gram-negative origin. The Poribacteria produce at least two polyketide synthases (PKSs), one of which is the sponge-specific Sup-type PKS. Several putative symbiosis factors such as adhesins (bacterial Ig-like domains, lamininin G domain proteins), adhesin-related proteins (ankyrin, fibronectin type III) and tetratrico peptide repeat domain-encoding proteins were identified, which might be involved in mediating sponge–microbe interactions. The discovery of genes coding for 24-isopropyl steroids implies that certain fossil biomarkers used to date the origins of metazoan life on earth may possibly be of poribacterial origin. Single-cell genomic approaches, such as those shown herein, contribute to a better understanding of beneficial microbial consortia, of which most members are, because of the lack of cultivation, inaccessible by conventional techniques.     

Fluorescence in situ hybridization for intracellular localization of nifH mRNA

Few reports on in situ mRNA detection in bacteria have been published, even though a major aim in environmental microbiology is to link function/activity to the identity of the organisms. This study reports a reliable approach for the in situ detection of nifH mRNA using fluorescence hybridization based on a previously described protocol for pmoA. nifH codes for a dinitrogenase reductase, a key enzyme in dinitrogen fixation. nifH mRNA was hybridized with a digoxigenin-labelled polynucleotide probe. The hybrid was detected with an anti-DIG-antibody labelled with horseradish peroxidase. Subsequently, the signal was amplified by catalyzed reporter deposition (CARD) with fluorochrome-labelled tyramides. Furthermore, the imaged organisms were identified using standard fluorescence in situ hybridization of rRNA. Thus, the approach enabled us specifically to link in situ the information from the dinitrogen fixation activity of an organism to its identity. Unexpectedly, the signals derived from nifH mRNA hybridization showed a distinct uneven pattern within the cells. This indicated that the method used could even give insights about the localization of the detected mRNA within the cell, which is a potential use of mRNA fluorescence in situ hybridization (FISH) that has not been reported up to now for bacterial cells.     

Bacterial community diversity associated with four marine sponges from the South China Sea based on 16S rDNA-DGGE fingerprinting

Culture-independent 16S rDNA-DGGE fingerprinting and phylogenetic analysis were used to reveal the community structure and diversity of the predominant bacteria associated with the four sponges Stelletta tenui, Halichrondria, Dysidea avara, and Craniella australiensis from the South China Sea for the first time. Sponge total community DNA extracted with a direct grinding disruption based method was used successfully after series dilution for 16S rDNA PCR amplification, which simplifies the current procedure and results in good DGGE banding profiles. 16S rDNA-V3 fragments from 42 individual DGGE bands were sequenced and the detailed corresponding bacteria were found in sponges for the fist time based on BLAST results. The sponge-associated bacteria are sponge host-specific because each of the tested four sponges from the same geographical location has different predominant bacterial diversity. Proteobacteria, e.g. α, β and γ subdivisions, make up the majority of the predominant bacteria in sponges and are perhaps in close symbiotic relationship with sponges. Though similar bacteria with close phylogenetic relationships were found among different sponges, the sponge-associated predominant bacterial community structures differ. Sponge C. australiensis has the greatest bacterial diversity, with the four bacteria phyla Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria, followed by the sponge D. avara with the two phyla Proteobacteria and Bacteroidetes, and the sponges S. tenui and Halichrondria with the phylum Proteobacteria. DGGE fingerprint-based analysis should ideally be integrated with band cloning and sequencing, phylogenetic analysis and molecular techniques to obtain precise results in terms of the microbial community and diversity.     

Non-rigid cryptic sponges in oyster patch reefs (Lower Kimmeridgian, Langenberg/Oker, Germany)

Summary Two patch reefs which predominately consist of the oysterNanogyra nana (Sowerby 1822) are exposed in Lower Kimmeridigian strata of the Langenberg hillrange, central Germany. Left oyster valves making up the frame-work of the reefs formed small abundant cavities that were inhabited by a unique sponge community. The excellent preservation of non-rigid sponges was related to early organomineralization within the decaying sponge tissue. As a process of sponge taphonomy, different types of microbially induced carbonates precipitated preserving spicule aggregates. Organomineralization within sponge soft tissues is especially favored with the Langenberg patch reefs due to the closed or semi-closed system conditions with the cavities. The δ¹³C values ofin situ formed microbialities reveal that carbonate precipitation was in equilibrium with Jurassic seawater. The carbon of the microbialites does not derive from the bacterial remineralization of organic matter, but is of a marine source. Likewise, organomineralization is probably related to bacterial EPS or decaying sponge tissues providing an organic matrix for initial carbonate precipitation. Biomarker analyses revealed, that the patch reef microbialites contain terminally branched fatty acids (iso-andanteiso-pentadecanoic acid) in significant concentrations. These fatty acids, like hopanoid hydrocarbons, are most likely of a bacterial source. This is in agreement with sulfate-reducing bacteria remineralizing the decaying sponges as further indicated by the occurrence of framboidal pyrite in sponge microbialites.     

Specificity of bacterial symbionts in Mediterranean and Great Barrier Reef sponges

Bacteria were isolated from marine sponges from the Mediterranean and the Great Barrier Reef and characterized using numerical taxonomy techniques. A similar sponge-specific bacterial symbiont was found in 9 of 10 sponges examined from both geographic regions. This symbiont occurred in sponges of two classes and seven orders, and it probably has been associated with sponges over a long geological time scale. Another symbiont apparently specific to the spongeVerongia aerophoba was found. This sponge is yellow-orange, similar in color to the bacterial symbiont. These symbionts are two of a large mixed bacterial population present in many sponges.This paper constitutes No. V in the series Microbial Associations in Sponges.     

Quantitative comparison of bacterial communities in two Mediterranean sponges

Marine sponges can host in their tissues abundant and diverse bacterial communities. Lack of truly quantitative data on bacterial abundance and dynamics limits our understanding of the organization and functioning of these endobiotic communities. In this technical note, we describe a quantitative polymerase chain reaction approach to quantify the relative abundance of multiple clades of three major sponge-associated bacterial phyla: Chloroflexi, Acidobacteria, and Actinobacteria. To test our approach we used the Mediterranean sponges Spongia lamella and Aplysina aerophoba. We designed five out of the six primer sets used in our study. We tested the new primer sets for specificity and optimized their conditions. Our preliminary data showed that Spongia lamella had larger bacterial abundance than Aplysina aerophoba, except for one clade of Chloroflexi. The two Chloroflexi clades investigated in our study amplified a fraction of the Chloroflexi present in Spongia lamella and most of what is present in Aplysina aerophoba, suggesting a more diverse Chloroflexi population in Spongia lamella than in Aplysina aerophoba. This quantitative technique has a great potential to provide a rapid and robust assessment of sponge microbial target and could contribute to deciphering the complexity of these largely unknown host-symbiont interactions.     

Morphological,Bacterial, and Secondary Metabolite Changes of <Emphasis Type="Italic">Aplysina aerophoba</Emphasis> upon Long-Term Maintenance Under Artificial Conditions

The aim of this study was to analyze successional changes in the bacterial community over a period of 6 months of cultivation of Aplysina aerophoba sponges under different artificial cultivation conditions by use of denaturing gradient gel electrophoresis (DGGE). The cultivation conditions varied concerning the water temperature (20 ± 2 °C and 25 ± 2 °C) of the aquaria, additional illumination of one aquarium, and feeding of the sponges. Amplicons from DGGE separation of dominant colonizing or variably appearing bacteria were sequenced and aligned for taxonomical identification. In addition, secondary metabolites typically found in A. aerophoba were analyzed to investigate changes in the natural product profile during cultivation. The cultivation of sponges under any given condition did not lead to a depletion of their bacterial community in the course of the experiment. On the contrary, the distinctive set of associated bacteria was maintained in spite of a dramatic loss of biomass and morphological degradation during the cultivation period. Generally, all sequences obtained from the DGGE gels were related to bacteria of five phyla: Actinobacteria, Cyanobacteria, α-Proteobacteria, γ-Proteobacteria, and Chloroflexi. Despite the overall stability of the bacterial community in A. aerophoba, an unambiguous variability was detected for the Cyanobacteria “A. aerophoba clone TK09”. This variability was ascribed to the predominant light conditions. The analysis of the metabolic pattern revealed that the concentration of a class of characteristic-brominated compounds typically found in A. aerophoba, like aeroplysinin-1, aerophobin-1, aerophobin-2, and isofistularin-3, increased over the 6 months of cultivation.     

Assessing the complex sponge microbiota: core,variable and species-specific bacterial communities in marine sponges

Marine sponges are well known for their associations with highly diverse, yet very specific and often highly similar microbiota. The aim of this study was to identify potential bacterial sub-populations in relation to sponge phylogeny and sampling sites and to define the core bacterial community. 16S ribosomal RNA gene amplicon pyrosequencing was applied to 32 sponge species from eight locations around the world''s oceans, thereby generating 2567 operational taxonomic units (OTUs at the 97% sequence similarity level) in total and up to 364 different OTUs per sponge species. The taxonomic richness detected in this study comprised 25 bacterial phyla with Proteobacteria, Chloroflexi and Poribacteria being most diverse in sponges. Among these phyla were nine candidate phyla, six of them found for the first time in sponges. Similarity comparison of bacterial communities revealed no correlation with host phylogeny but a tropical sub-population in that tropical sponges have more similar bacterial communities to each other than to subtropical sponges. A minimal core bacterial community consisting of very few OTUs (97%, 95% and 90%) was found. These microbes have a global distribution and are probably acquired via environmental transmission. In contrast, a large species-specific bacterial community was detected, which is represented by OTUs present in only a single sponge species. The species-specific bacterial community is probably mainly vertically transmitted. It is proposed that different sponges contain different bacterial species, however, these bacteria are still closely related to each other explaining the observed similarity of bacterial communities in sponges in this and previous studies. This global analysis represents the most comprehensive study of bacterial symbionts in sponges to date and provides novel insights into the complex structure of these unique associations.     

16S rDNA clone library-based bacterial phylogenetic diversity associated with three South China Sea sponges

Culture-independent molecular techniques, 16S rDNA clone library alongside RFLP and phylogenetic analysis, were applied to investigate the bacterial diversity associated with three South China Sea sponges, Stelletta tenui, Halichondria rugosa and Dysidea avara. A wide bacterial diversity was detected according to total genomic DNA-based 16S rDNA clone library, abundant clones with low identify with sequences retrieved from database were found as well as uncultured sponge symbionts. The phylogenetic analysis shows that the bacterial community structure of Stelletta tenui is similar to that of Halichondria rugosa comprising gamma-Proteobacteria and Firmicutes. Whereas, alpha-Proteobacteria, gamma-Protebacteria, Bacteroidetes and uncultured sponge symbionts were found in sponge Dysidea avara, suggesting that Dysidea avara has the highest bacteria diversity among these sponges. A specific sponge–microbe association is suggested based on the difference of bacterial diversity among these three sponges from the same geography location and the observed sponge species-specific bacteria.     

Bacterial Diversity Associated with Cinachyra cavernosa and Haliclona pigmentifera,Cohabiting Sponges in the Coral Reef Ecosystem of Gulf of Mannar,Southeast Coast of India

Sponges are abundant, diverse and functionally important organisms of coral reef ecosystems. Sponge-associated microorganisms have been receiving greater attention because of their significant contribution to sponge biomass, biogeochemical cycles and biotechnological potentials. However, our understanding of the sponge microbiome is limited to a few species of sponges from restricted geographical locations. Here, we report for the first time the bacterial diversity of two cohabiting sponges, viz. Cinachyra cavernosa and Haliclona pigmentifera, as well as that in the ambient water from the coral reef ecosystems of the Gulf of Mannar, located along the southeast coast of India. Two hundred and fifty two clones in the 16S rRNA gene library of these sponges were grouped into eight distinct phyla, of which four belonged to the core group that are associated only with sponges. Phylogenetic analysis of the core bacteria showed close affinity to other sponge-associated bacteria from different geographical locations. γ-Proteobacteria, Chloroflexi, Planctomycetes and Deferribacter were the core groups in C. cavernosa while β and δ-Proteobacteria performed this role in H. pigmentifera. We observed greater OTU diversity for C. cavernosa (H^ǀ 2.07) compared to H. pigmentifera (H^ǀ 1.97). UniFrac analysis confirmed the difference in bacterial diversity of the two sponge species and also between the sponges and the reef water (p<0.001). The results of our study restate the existence of a host driven force in shaping the sponge microbiome.     

Chemical variability within the marine sponge Aplysina fulva

Dibromotyrosine-derived metabolites are of common occurrence within marine sponges belonging to the order Verongida. However, previous chemical analysis of crude extracts obtained from samples of the verongid sponge Aplysina fulva collected in Brazil did not provide any dibromotyrosine-derived compounds. In this investigation, five samples of A. fulva from five different locations along the Brazilian coastline and one sample from a temperate reef in the South Atlantic Bight (SAB) (Georgia, USA) were investigated for the presence of bromotyrosine-derived compounds. All six samples collected yielded dibromotyrosine-derived compounds, including a new derivative, named aplysinafulvin, which has been identified by analysis of spectroscopic data. These results confirm previous assumptions that dibromotyrosine-derived metabolites can be considered as chemotaxonomic markers of verongid sponges. The isolation of aplysinafulvin provides additional support for a biogenetic pathway involving an arene oxide intermediate in the biosynthesis of Verongida metabolites. It cannot yet be established if the chemical variability observed among the six samples of A. fulva collected in Brazil and the SAB is the result of different environmental factors, distinct chemical extraction and isolation protocols, or a consequence of hidden genetic diversity within the postulated morphological plasticity of this species.     

Molecular Microbial Diversity Survey of Sponge Reproductive Stages and Mechanistic Insights into Vertical Transmission of Microbial Symbionts

Many marine sponges, hereafter termed high-microbial-abundance (HMA) sponges, harbor large and complex microbial consortia, including bacteria and archaea, within their mesohyl matrices. To investigate vertical microbial transmission as a strategy to maintain these complex associations, an extensive phylogenetic analysis was carried out with the 16S rRNA gene sequences of reproductive (n = 136) and adult (n = 88) material from five different Caribbean species, as well as all published 16S rRNA gene sequences from sponge offspring (n = 116). The overall microbial diversity, including members of at least 13 bacterial phyla and one archaeal phylum, in sponge reproductive stages is high. In total, 28 vertical-transmission clusters, defined as clusters of phylotypes that are found both in adult sponges and their offspring, were identified. They are distributed among at least 10 bacterial phyla and one archaeal phylum, demonstrating that the complex adult microbial community is collectively transmitted through reproductive stages. Indications of host-species specificity and cospeciation were not observed. Mechanistic insights were provided using a combined electron microscopy and fluorescence in situ hybridization analysis, and an indirect mechanism of vertical transmission via nurse cells is proposed for the oviparous sponge Ectyoplasia ferox. Based on these phylogenetic and mechanistic results, we suggest the following symbiont transmission model: entire microbial consortia are vertically transmitted in sponges. While vertical transmission is clearly present, additional environmental transfer between adult individuals of the same and even different species might obscure possible signals of cospeciation. We propose that associations of HMA sponges with highly sponge-specific microbial communities are maintained by this combination of vertical and horizontal symbiont transmission.     

Florida reef sponges harbor coral disease-associated microbes

Sponges can filter large volumes of seawater and accumulate highly diverse and abundant microbial communities within their tissue. Culture-independent techniques such as fluorescent in situ hybridization (FISH), 16S small subunit (SSU) rRNA gene analyses, and transmission electron microscopy (TEM) were applied to characterize the presence and distribution of microbes within sponges abundant on south Florida reefs. This study found that coral disease-associated bacteria (CDAB) are harbored within Agelas tubulata and Amphimedon compressa. FISH probes detected several potential bacterial pathogens such as Aurantimonas coralicida, Cytophaga sp., Desulfovibrio spp, Serratia marcescans, and Vibrio mediterranei within A. compressa and A. tubulata host sponges. Spatial differences in the distribution of targeted bacteria were seen within sponge hosts. Transmission electron microscopy of A. compressa indicated there was a higher concentration of bacteria in the choanosome compared to the ectosome. These observed spatial distributions support the presence of internal sponge niches, which could play a role in the location of the CDAB within the sponges.     

Biogeography and Host Fidelity of Bacterial Communities in Ircinia spp. from the Bahamas

Research on sponge microbial assemblages has revealed different trends in the geographic variability and specificity of bacterial symbionts. Here, we combined replicated terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of 16S rRNA gene sequences to investigate the biogeographic and host-specific structure of bacterial communities in two congeneric and sympatric sponges: Ircinia strobilina, two color morphs of Ircinia felix and ambient seawater. Samples were collected from five islands of the Bahamas separated by 80 to 400 km. T-RFLP profiles revealed significant differences in bacterial community structure among sponge hosts and ambient bacterioplankton. Pairwise statistical comparisons of clone libraries confirmed the specificity of the bacterial assemblages to each host species and differentiated symbiont communities between color morphs of I. felix. Overall, differences in bacterial communities within each host species and morph were unrelated to location. Our results show a high degree of symbiont fidelity to host sponge across a spatial scale of up to 400 km, suggesting that host-specific rather than biogeographic factors play a primary role in structuring and maintaining sponge–bacteria relationships in Ircinia species from the Bahamas.