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The cold-water coral Lophelia pertusa (Scleractinia, Caryophylliidae) is a key species in the formation of cold-water reefs, which are among the most diverse deep-sea ecosystems. It occurs in two color varieties: white and red. Bacterial communities associated with Lophelia have been investigated in recent years, but the role of the associated bacteria remains largely obscure. This study uses catalyzed reporter deposition fluorescence in situ hybridization to detect the in situ location of specific bacterial groups on coral specimens from the Trondheimsfjord (Norway). Two tissue-associated groups were identified: (i) bacteria on the host's tentacle ectoderm, “Candidatus Mycoplasma corallicola,” are flasklike, pointed cells and (ii) endoderm-associated bona fide TM7 bacteria form long filaments in the gastral cavity. These tissue-bound bacteria were found in all coral specimens from the Trondheimsfjord, indicating a closer relationship with the coral compared to bacterial assemblages present in coral mucus and gastric fluid.

The pseudocolonial coral Lophelia pertusa (Scleractinia, Caryophylliidae) is a eury¬ba¬thic, steno¬ther¬mal cosmopolitan cold-water species. It occurs in two colour vari¬eties, white and red. L. pertusa builds vast cold-water coral reefs along the con¬tinental margins, which are among the most diverse deep-sea ecosystems. Micro¬biology of L. pertusa has been in scientific focus for only a few years. The question whether the coral holds a host-specific bac¬te¬rial commu¬nity is not finally answered. Possible implications of the two colour varieties for microbial colonisation must be taken into account. Bio imaging can reveal the in-situ location of bacterial groups on and possible interactions with the coral. The pre¬sent study aimed at investigating these aspects, drawing a more compre¬hen¬sive pic¬ture of commu¬nity struc¬ture, taxo¬no¬my, and in-situ location of L. pertusa-hosted microbes.

The pseudocolonial coral Lophelia pertusa (Scleractinia, Caryophylliidae) is a eurybathic, stenothermal cosmopolitan cold-water species. It occurs in two color varieties, white and red. L. pertusa builds vast cold-water coral reefs along the continental margins, which are among the most diverse deep-sea habitats. Microbiology of L. pertusa has been in scientific focus for only a few years, but the question of whether the coral holds a host-specific bacterial community has not been finally answered. Bacteria on coral samples from the Trondheimsfjord (Norway) were characterized by the culture-independent 16S rRNA gene-based techniques terminal restriction fragment length polymorphism and sequence analysis. L. pertusa revealed a high microbial richness. Clone sequences were dominated by members of the Alpha- and Gammaproteobacteria. Other abundant taxa were Bacteroidetes, Actinobacteria, Verrucomicrobia, Firmicutes, and Planctomycetes. The bacterial community of L. pertusa not only differed conspicuously from that of the environment but also varied with both the location and color variety of its host. Therefore, the microbial colonization cannot be termed “specific” sensu stricto. However, similarities to other coral-bacterium associations suggest the existence of “cold-water coral-specific” bacterial groups sensu lato. L. pertusa-associated bacteria appear to play a significant role in the nutrition of their host by degradation of sulfur compounds, cellulose, chitin, and end products of the coral's anaerobic metabolism. Some coral-associated microbes were regarded as opportunistic pathogens. Dominance of mixotrophic members of the Rhodobacteraceae in white L. pertusa could explain the wider dispersal of this phenotype by supplementary nutrition.

The local distribution of the bacterial community associated with the marine sponge Tethya aurantium Pallas 1766 was studied. Distinct bacterial communities were found to inhabit the endosome and cortex. Clear differences in the associated bacterial populations were demonstrated by denaturing gradient gel electrophoresis (DGGE) and analysis of 16S rRNA gene clone libraries. Specifically associated phylotypes were identified for both regions: a new phylotype of Flexibacteria was recovered only from the sponge cortex, while Synechococcus species were present mainly in the sponge endosome. Light conduction via radiate spicule bundles conceivably facilitates the unusual association of Cyanobacteria with the sponge endosome. Furthermore, a new monophyletic cluster of sponge-derived 16S rRNA gene sequences related to the Betaproteobacteria was identified using analysis of 16S rRNA gene clone libraries. Members of this cluster were specifically associated with both cortex and endosome of T. aurantium.

The family Solemyidae represents ancestral protobranch bivalves with the shallow-water genus Solemya and the deep-sea genus Acharax. All known members of this family host symbiotic sulfur-oxidizing bacteria in their gill filaments. Analysis of 18S rRNA gene sequences of Acharax specimens from methane-seeps off Makran (Pakistan), Java (Indonesia), the Aleutian Trench and off the Oregon, Costa Rica, and Peru margins revealed that Solemya spp. and Acharax spp. are well-separated genetically. This supports the current systematic distinction based on morphological criteria. We found 2 clearly distinct clusters within the genus Acharax, with specimens from the Makran, Oregon and Peru (MOP) margins in one (MOP–Acharax) cluster, and those from Java, the Aleutian Trench and Costa Rica (JAC) in the other (JAC–Acharax) cluster. The separation of MOP– and JAC–Acharax clusters from each other and from Solemya (S. reidi and S. velum) is well-supported by phylogenetic calculations employing maximum likelihood and maximum parsimony. Compared to genetic distances among other protobranch groups, distances between the MOP– and JAC–Acharax clusters would justify the affiliation of these clusters to separate species. This implies that species differentiation in Acharax based on shell morphology is likely to underestimate true species diversity within this taxon. Furthermore, our results support the hypothesis that genetic separation of Solemya and Acharax is congruent with the phylogeny of their bacterial endosymbionts.