title: Complete ecological isolation and cryptic diversity in Polynucleobacter bacteria not resolved by 16S rRNA gene sequences.
abstract: Transplantation experiments and genome comparisons were used to determine if lineages of planktonic Polynucleobacter almost indistinguishable by their 16S ribosomal RNA (rRNA) sequences differ distinctively in their ecophysiological and genomic traits. The results of three transplantation experiments differing in complexity of biotic interactions revealed complete ecological isolation between some of the lineages. This pattern fits well to the previously detected environmental distribution of lineages along chemical gradients, as well as to differences in gene content putatively providing adaptation to chemically distinct habitats. Patterns of distribution of iron transporter genes across 209 Polynucleobacter strains obtained from freshwater systems and representing a broad pH spectrum further emphasize differences in habitat-specific adaptations. Genome comparisons of six strains sharing ⩾99% 16S rRNA similarities suggested that each strain represents a distinct species. Comparison of sequence diversity among genomes with sequence diversity among 240 cultivated Polynucleobacter strains indicated a large cryptic species complex not resolvable by 16S rRNA sequences. The revealed ecological isolation and cryptic diversity in Polynucleobacter bacteria is crucial in the interpretation of diversity studies on freshwater bacterioplankton based on ribosomal sequences.
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondsee, Austria.
authors.forename: Martin W
authors.identifier: 0000-0003-0501-2556
authors.initials: MW
authors.lastname: Hahn
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondsee, Austria.|Biology Centre of the ASCR, v.v.i., Institute of Hydrobiology, České Budějovice, Czech Republic.
authors.forename: Jitka
authors.initials: J
authors.lastname: Jezberová
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondsee, Austria.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Koll
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondsee, Austria.
authors.forename: Tanja
authors.initials: T
authors.lastname: Saueressig-Beck
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondsee, Austria.
authors.forename: Johanna
authors.initials: J
authors.lastname: Schmidt
mesh_terms: D042521:Burkholderiaceae / Q000235:genetics* / Q000302:isolation & purification; D004269:DNA, Bacterial / Q000235:genetics; D004463:Ecology; D017753:Ecosystem; D005618:Fresh Water / Q000382:microbiology*; D023281:Genomics; D010802:Phylogeny; D010933:Plankton / Q000235:genetics* / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S