title: Ménage-à-trois: the amoeba Nuclearia sp. from Lake Zurich with its ecto- and endosymbiotic bacteria.
abstract: We present a fascinating triad relationship between a eukaryotic amoeba and its two bacterial symbionts. The morphological characteristics of the amoeba allowed for a confident assignment to the genus Nuclearia (Opisthokonta, Nucleariidae), but species identification resulted in an ambiguous result. Sequence analysis indicated an affiliation to the species N. thermophila, however, several morphological features contradict the original description. Amoebal isolates were cultured for several years with their preferred food source, the microcystin-producing harmful cyanobacterium Planktothrix rubescens. Symbioses of the amoeba with ecto- and endosymbiotic bacteria were maintained over this period. Several thousand cells of the ectosymbiont are regularly arranged inside a layer of extracellular polymeric substances produced by the amoeba. The ectosymbiont was identified as Paucibacter toxinivorans (Betaproteobacteria), which was originally isolated by enrichment with microcystins. We found indications that our isolated ectosymbiont indeed contributed to toxin-degradation. The endosymbiont (Gammaproteobacteria, 15-20 bacteria per amoeba) is enclosed in symbiosomes inside the host cytoplasm and represents probably an obligate symbiont. We propose the name "Candidatus Endonucleariobacter rarus" for this bacterium that was neither found free-living nor in a symbiotic association. Nucleariidae are uniquely suited model organisms to study the basic principles of symbioses between opisthokonts and prokaryotes.
authors.affiliation: Limnological Station, Institute of Plant Biology, University of Zurich, Seestrasse 187, CH-8802 Kilchberg, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Dirren
authors.affiliation: Limnological Station, Institute of Plant Biology, University of Zurich, Seestrasse 187, CH-8802 Kilchberg, Switzerland; Biology Centre of the Academy of Sciences of the Czech Republic, Institute of Hydrobiology, Na Sádkách 7, CZ-37005 České Budějovice, Czech Republic.
authors.forename: Michaela M
authors.initials: MM
authors.lastname: Salcher
authors.affiliation: Limnological Station, Institute of Plant Biology, University of Zurich, Seestrasse 187, CH-8802 Kilchberg, Switzerland.
authors.forename: Judith F
authors.initials: JF
authors.lastname: Blom
authors.affiliation: Department of Zoology, Institute for Biomaterials and biomolecular Systems, University of Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schweikert
authors.affiliation: Limnological Station, Institute of Plant Biology, University of Zurich, Seestrasse 187, CH-8802 Kilchberg, Switzerland. Electronic address: posch@limnol.uzh.ch.
authors.forename: Thomas
authors.initials: T
authors.lastname: Posch
mesh_terms: D000656:Amoeba / Q000145:classification / Q000166:cytology / Q000302:isolation & purification* / Q000382:microbiology*; D020562:Betaproteobacteria / Q000145:classification* / Q000302:isolation & purification* / Q000502:physiology; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D020563:Gammaproteobacteria / Q000145:classification* / Q000302:isolation & purification* / Q000502:physiology; D020459:Genes, rRNA; D060106:Lakes / Q000469:parasitology; D008969:Molecular Sequence Data; D016053:RNA, Protozoan / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013557:Switzerland; D013559:Symbiosis
chemical_list: D004269:DNA, Bacterial; D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D016053:RNA, Protozoan; D012336:RNA, Ribosomal, 16S; D012337:RNA, Ribosomal, 18S
keywords: Bacteria-protist symbioses; Nucleariidae; Paucibacter toxinivorans.; ectosymbionts; endosymbionts; feeding