Data from: Specificity in diversity: single origin of a widespread ciliate-bacteria symbiosis

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.