title: Global phylogeography of pelagic Polynucleobacter bacteria: restricted geographic distribution of subgroups, isolation by distance and influence of climate.
abstract: The free-living planktonic freshwater bacterium Polynucleobacter necessarius subspecies asymbioticus (> 99% 16S rRNA similarity) represents a taxon with a cosmopolitan distribution and apparently ubiquitous occurrence in lentic freshwater habitats. We tested for intra-taxon biogeographic patterns by combining cultivation-independent and cultivation methods. A culture collection of 204 strains isolated from globally distributed freshwater habitats (Arctic to Antarctica) was investigated for phylogeographic patterns based on sequences of two markers, the 16S-23S internal transcribed spacers and the glutamine synthetase gene (glnA). Genetic distance between isolates showed significant geographic distance-decay patterns for both markers, suggesting that an isolation-by-distance mechanism influences the global phylogeography. Furthermore, a couple of subgroups showed restricted geographic distributions. Strains of one subgroup were exclusively obtained from tropical sites on four continents (pantropical subgroup). Cultivation-independent methods were used to confirm the restricted geographic distributions of two subgroups. The pantropical taxon could be detected in 63% of investigated tropical habitats but not in any of 121 European freshwater samples. Physiological tests indicated that almost all strains of the pantropical subgroup failed to grow at temperatures of 4°C, while strains affiliated with other subgroups showed good growth at this temperature. This suggests that thermal adaptation is involved in phylogeographic structuring of the global Polynucleobacter population.
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondseestrasse 9, A-5310, Mondsee, Austria.
authors.forename: Martin W
authors.initials: MW
authors.lastname: Hahn
authors.forename: Ulrike
authors.initials: U
authors.lastname: Koll
authors.forename: Jitka
authors.initials: J
authors.lastname: Jezberová
authors.forename: Antonio
authors.initials: A
authors.lastname: Camacho
mesh_terms: D001483:Base Sequence; D042521:Burkholderiaceae / Q000145:classification* / Q000235:genetics*; D002980:Climate; D004269:DNA, Bacterial / Q000235:genetics; D017753:Ecosystem; D005618:Fresh Water / Q000382:microbiology*; D005974:Glutamate-Ammonia Ligase / Q000235:genetics; D010802:Phylogeny; D058974:Phylogeography; D010933:Plankton / Q000235:genetics / Q000382:microbiology*; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012338:RNA, Ribosomal, 23S / Q000235:genetics; D022661:RNA, Untranslated / Q000235:genetics; D013696:Temperature
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S; D012338:RNA, Ribosomal, 23S; D022661:RNA, Untranslated; D005974:Glutamate-Ammonia Ligase