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FEMS Microbiol Ecol. 2009 Feb;67(2):229-41. doi: 10.1111/j.1574-6941.2008.00628.x.

High genetic similarity between two geographically distinct strains of the sulfur-oxidizing symbiont 'Candidatus Thiobios zoothamnicoli'.

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1
Department of Marine Biology, University of Vienna, Vienna, Austria. rinke@gmx.at

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.

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