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- Bergin, Claudia, et al.
(författare)
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Acquisition of a Novel Sulfur-Oxidizing Symbiont in the Gutless Marine Worm Inanidrilus exumae
- 2018
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Ingår i: Applied and Environmental Microbiology. - : AMER SOC MICROBIOLOGY. - 0099-2240 .- 1098-5336. ; 84:7
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Tidskriftsartikel (refereegranskat)abstract
- Gutless marine oligochaetes (Annelida, Clitellata) lack a digestive and excretory system, and live in an obligate association with multiple bacterial endosymbionts that supply them with nutrition. In this study, we discovered an unusual symbiont community in the gutless oligochaete Inanidrilus exumae that differs markedly from the microbiome of all other 22 examined host species. Comparative 16S rRNA sequence analysis and fluorescence in situ hybridization revealed that I.exumae harboured co-occurring gamma-, alpha- and deltaproteobacterial symbionts, while all other host species harbour gamma- and either alpha- or deltaproteobacterial symbionts. Surprisingly, the primary chemoautotrophic, sulfur-oxidizer, Ca. Thiosymbion, which occurs in all other gutless oligochaetes, does not appear to be present in I.exumae. Instead, I. exumae harboured a bacterial endosymbiont that resembled Ca. Thiosymbion morphologically and metabolically, but originated from a novel lineage within the Gammaproteobacteria. This endosymbiont, named Gamma 4 symbiont here, had a 16S rRNA sequence that differed by at least 7% from those of other free-living and symbiotic bacteria and by 10% from Ca. Thiosymbion. Sulfur globules in the Gamma 4 symbiont cells, as well as the presence of genes characteristic for autotrophy (cbbL) and sulfur oxidation (aprA), suggest that this symbiont is a chemoautotrophic sulfur oxidizer. Our results indicate that a novel lineage of free-living bacteria was able to establish a stable and specific association with I. exumae, and displace the Ca. Thiosymbion symbionts originally associated with these hosts.
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| 2. |
- Zimmermann, Judith, et al.
(författare)
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Closely coupled evolutionary history of ecto- and endosymbionts from two distantly-related animal phyla : Closely linked ecto- and endosymbiont evolution
- 2016
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Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 25:13, s. 3203-3223
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Tidskriftsartikel (refereegranskat)abstract
- The level of integration between associated partners can range from ectosymbioses to extracellular and intracellular endosymbioses, and this range has been assumed to reflect a continuum from less intimate to evolutionarily highly stable associations. In this study, we examined the specificity and evolutionary history of marine symbioses in a group of closely related sulphur-oxidizing bacteria, called Candidatus Thiosym- bion, that have established ecto- and endosymbioses with two distantly related animal phyla, Nematoda and Annelida. Intriguingly, in the ectosymbiotic associations of stil- bonematine nematodes, we observed a high degree of congruence between symbiont and host phylogenies, based on their ribosomal RNA (rRNA) genes. In contrast, for the endosymbioses of gutless phallodriline annelids (oligochaetes), we found only a weak congruence between symbiont and host phylogenies, based on analyses of sym- biont 16S rRNA genes and six host genetic markers. The much higher degree of con- gruence between nematodes and their ectosymbionts compared to those of annelids and their endosymbionts was confirmed by cophylogenetic analyses. These revealed 15 significant codivergence events between stilbonematine nematodes and their ectosym- bionts, but only one event between gutless phallodrilines and their endosymbionts. Phylogenetic analyses of 16S rRNA gene sequences from 50 Cand. Thiosymbion spe- cies revealed seven well-supported clades that contained both stilbonematine ectosym- bionts and phallodriline endosymbionts. This closely coupled evolutionary history of marine ecto- and endosymbionts suggests that switches between symbiotic lifestyles and between the two host phyla occurred multiple times during the evolution of the Cand. Thiosymbion clade, and highlights the remarkable flexibility of these symbiotic bacteria.
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