Symbioses between eukaryotes and sulfur-oxidizing (thiotrophic) bacteria have convergently evolved multiple times. Although well described in at least eight classes of metazoan animals, almost nothing is known about the evolution of thiotrophic symbioses in microbial eukaryotes (protists). In this study, we characterized the symbioses between mouthless marine ciliates of the genus Kentrophoros, and their thiotrophic bacteria, using comparative sequence analysis and fluorescence in situ hybridization. Ciliate small-subunit rRNA sequences were obtained from 17 morphospecies collected in the Mediterranean and Caribbean, and symbiont sequences from 13 of these morphospecies. We discovered a new Kentrophoros morphotype where the symbiont-bearing surface is folded into pouch-like compartments, illustrating the variability of the basic body plan. Phylogenetic analyses revealed that all investigated Kentrophoros belonged to a single clade, despite the remarkable morphological diversity of these hosts. The symbionts were also monophyletic and belonged to a new clade within the Gammaproteobacteria, with no known cultured representatives. Each host morphospecies had a distinct symbiont phylotype, and statistical analyses revealed significant support for host–symbiont codiversification. Given that these symbioses were collected from two widely separated oceans, our results indicate that symbiotic associations in unicellular hosts can be highly specific and stable over long periods of evolutionary time.
Kentrophoros sp. H sample 500-10 aligned section stack
Aligned image stack of semithin sections in Amira format. Kentrophoros sp. H collected 6 Nov 2014 from Cavoli, Isola d'Elba, Italy, fixed in 2.5% glutaraldehyde, post-fixed 1% osmium tetroxide, embedded in Epon resin. Serial sections stained with toluidine blue and imaged in greyscale. Image stack automatically aligned with manual refinement.
Kentrophoros50010.align.filtered-3.align-crop.am
Kentrophoros sp. H sample 500-10 aligned section stack - edited
Same as "Kentrophoros sp. H sample 500-10 aligned section stack", but inverted in grayscale and modified to exclude background. Aligned image stack in Amira format.
Kentrophoros50010.align.filtered-3.align-crop-inverted.modif.am
Kentrophoros sp. H sample 500-19 aligned section stack
Aligned image stack of semithin sections in Amira format. Kentrophoros sp. H collected Nov 2014 from Cavoli, Isola d'Elba, Italy, fixed in 1% osmium tetroxide, embedded in Epon resin. Serial sections stained with toluidine blue and imaged in greyscale. Image stack automatically aligned with manual refinement.
Kentrophoros-50019+new.align.filtered.am
Kentrophoros sp. H sample 500-19 aligned section stack - edited
Same as "Kentrophoros sp. H sample 500-19 aligned section stack", but inverted in grayscale and modified to exclude background.
Kentrophoros-50019+new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median.modif.modif.am
Kentrophoros sp. H sample 500-10 pseudotrophosome labels
Kentrophoros sp. H sample 500-10 - label file to mark pseudotrophosome containing ectosymbionts. File in Amira format.
Kentrophoros50010.align.filtered-3.align-crop.labelsECTOTRO.am
Kentrophoros sp. H sample 500-10 pseudotrophosome surface
Kentrophoros sp. H sample 500-10 - surface file for pseudotrophosome containing ectosymbionts. File in Amira format.
Kentrophoros50010.align.filtered-3.align-crop.labelsECTOTRO4.smooth.am
Kentrophoros sp. H sample 500-10 ciliate cell labels
Kentrophoros sp. H sample 500-10 - label file to mark external boundary of ciliate cell. File in Amira format.
Kentrophoros50010.align.filtered-3.align-crop.labels.am
Kentrophoros sp. H sample 500-10 ciliate cell surface
Kentrophoros sp. H sample 500-10 - surface file for external boundary of ciliate cell. File in Amira format.
Kentrophoros50010.align.filtered-3.align-crop.labels5.smooth.am
Kentrophoros sp. H sample 500-10 nuclei labels
Kentrophoros sp. H sample 500-10 - label file to mark cell nuclei. File in Amira format.
Kentrophoros50010.align.filtered-3.align-crop.labelsNUCLEI.am
Kentrophoros sp. H sample 500-19 ciliate cell labels
Kentrophoros sp. H sample 500-19 - label file to mark external boundary of ciliate cell. File in Amira format.
Kentrophoros-50019-new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median-labelstotal.am
Kentrophoros sp. H sample 500-19 ciliate cell surface
Kentrophoros sp. H sample 500-19 - surface file for external boundary of ciliate cell. File in Amira format.
Kentrophoros-50019-new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median-labelstotal4.smooth.am
Kentrophoros sp. H sample 500-19 pseudotrophosome labels
Kentrophoros sp. H sample 500-19 - label file to mark pseudotrophosome containing ectosymbionts. File in Amira format.
Kentrophoros-50019+new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median.labels-ECTOTROPH_threshold.am
Kentrophoros sp. H sample 500-19 pseudotrophosome surface
Kentrophoros sp. H sample 500-19 - surface file for pseudotrophosome containing ectosymbionts. File in Amira format.
Kentrophoros-50019+new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median.labels-ECTOTROPH_threshold.surf.am
Kentrophoros sp. H sample 500-19 nuclei labels
Kentrophoros sp. H sample 500-19 - label file to mark cell nuclei. File in Amira format.
Kentrophoros-50019+new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median.labelsNUCLEI.am
Kentrophoros sp. H sample 500-19 nuclei surface
Kentrophoros sp. H sample 500-19 - surface file for cell nuclei. File in Amira format.
Kentrophoros-50019+new.align-crop-filtered-lanczos-filtered-contr1.5-inverted.modif.filtered-median.labelsNUCLEI2.smooth.am