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.

• Klíčová slova
• Bacteria-protist symbioses, Nucleariidae, Paucibacter toxinivorans., ectosymbionts, endosymbionts, feeding,
• MeSH
• Amoeba klasifikace   cytologie   izolace a purifikace   mikrobiologie   MeSH
• Betaproteobacteria klasifikace   izolace a purifikace   fyziologie   MeSH
• DNA bakterií chemie   genetika   MeSH
• Gammaproteobacteria klasifikace   izolace a purifikace   fyziologie   MeSH
• geny rRNA MeSH
• jezera parazitologie   MeSH
• mezerníky ribozomální DNA chemie   genetika   MeSH
• molekulární sekvence - údaje MeSH
• protozoální DNA chemie   genetika   MeSH
• ribozomální DNA chemie   genetika   MeSH
• RNA protozoální genetika   MeSH
• RNA ribozomální 16S genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• sekvenční analýza DNA MeSH
• symbióza * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Švýcarsko MeSH
• Názvy látek
• DNA bakterií MeSH
• mezerníky ribozomální DNA MeSH
• protozoální DNA MeSH
• ribozomální DNA MeSH
• RNA protozoální MeSH
• RNA ribozomální 16S MeSH
• RNA ribozomální 18S MeSH

We examined the effect of light on the heterotrophic activity of the filamentous cyanobacterium Planktothrix rubescens and on its relationship with the accompanying bacteria. In situ leucine uptake by bacteria and cyanobacteria was determined in a subalpine mesotrophic lake, and natural assemblages from the zone of maximal P. rubescens abundances were incubated for 2 days at contrasting light regimes (ambient, 100× increased, dark). Planktothrix rubescens from the photic zone of the lake incorporated substantially more leucine, but some heterotrophic activity was maintained in filaments from the hypolimnion. Exposure of cyanobacteria to increased irradiance or darkness resulted in significantly lower leucine incorporation than at ambient light conditions. Highest abundances and leucine uptake of Betaproteobacteria from the genus Limnohabitans were found in the accompanying microflora at suboptimal irradiance levels for P. rubescens or in dark incubations. Therefore, two Limnohabitans strains (representing different species) were co-cultured with axenic P. rubescens at different light conditions. The abundances and leucine incorporation rates of both strains most strongly increased at elevated irradiance levels, in parallel to a decrease of photosynthetic pigment fluorescence and the fragmentation of cyanobacterial filaments. Our results suggest that Limnohabitans spp. in lakes might profit from the presence of physiologically stressed P. rubescens.

• MeSH
• Comamonadaceae metabolismus   fyziologie   MeSH
• fotosyntéza fyziologie   MeSH
• heterotrofní procesy MeSH
• jezera mikrobiologie   MeSH
• leucin metabolismus   MeSH
• mikrobiologie vody * MeSH
• sinice metabolismus   fyziologie   MeSH
• světlo MeSH
• tma MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• leucin MeSH