title: High genetic similarity between two geographically distinct strains of the sulfur-oxidizing symbiont 'Candidatus Thiobios zoothamnicoli'.
abstract: The giant marine ciliate Zoothamnium niveum (Ciliophora, Oligohymenophora) is obligatorily covered by a monolayer of putative chemoautotrophic sulfur-oxidizing (thiotrophic) bacteria. For Z. niveum specimens from the Caribbean Sea it has been demonstrated that this ectosymbiotic population consists of only a single pleomorphic phylotype described as Candidatus Thiobios zoothamnicoli. The goal of our study was to identify and phylogenetically analyse the ectosymbiont(s) of a recently discovered Z. niveum population from the Mediterranean Sea, and to compare marker genes encoding key enzymes of the carbon and sulfur metabolism between the two symbiont populations. We identified a single bacterial phylotype representing the ectosymbiont of Z. niveum from the Mediterranean population showing 99.7% 16S rRNA gene (99.2% intergenic spacer region) similarity to the Caribbean Z. niveum ectosymbiont. Genes encoding enzymes typical for an inorganic carbon metabolism [ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO)] and for sulfur metabolism (5'-adenylylsulfate reductase, dissimilatory sulfite reductase) were detected in both symbiotic populations. The very high amino acid sequence identity (97-100%) and the high nucleic acid sequence identity (90-98%) of these marker enzymes in two geographically distant symbiont populations suggests that the association of Z. niveum with Cand. Thiobios zoothamnicoli is very specific as well as temporally and spatially stable.
authors.affiliation: Department of Marine Biology, University of Vienna, Vienna, Austria. rinke@gmx.at
authors.forename: Christian
authors.initials: C
authors.lastname: Rinke
authors.forename: Stephan
authors.initials: S
authors.lastname: Schmitz-Esser
authors.forename: Alexander
authors.initials: A
authors.lastname: Loy
authors.forename: Matthias
authors.initials: M
authors.lastname: Horn
authors.forename: Michael
authors.initials: M
authors.lastname: Wagner
authors.forename: Monika
authors.initials: M
authors.lastname: Bright
mesh_terms: D000818:Animals; D001419:Bacteria / Q000145:classification* / Q000201:enzymology / Q000235:genetics*; D052837:Chemoautotrophic Growth; D004275:DNA, Ribosomal / Q000032:analysis; D020459:Genes, rRNA; D008969:Molecular Sequence Data; D016802:Oligohymenophorea / Q000382:microbiology*; D010084:Oxidation-Reduction; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics; D017422:Sequence Analysis, DNA; D013455:Sulfur / Q000378:metabolism*; D013559:Symbiosis
chemical_list: D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S; D013455:Sulfur; D050862:Oxidoreductases Acting on Sulfur Group Donors; D012273:Ribulose-Bisphosphate Carboxylase