title: Lack of phylogeographic structure in the freshwater cyanobacterium Microcystis aeruginosa suggests global dispersal.
abstract: BACKGROUND
  Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographic structuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwater cyanobacterium Microcystis aeruginosa. Being widely distributed on a global scale but patchily on a regional scale, this prokaryote is an ideal model organism to study microbial dispersal and biogeography.
  
  
  RESULTS
  The phylogeography of M. aeruginosa was studied based on a dataset of 311 rDNA internal transcribed spacer (ITS) sequences sampled from six continents. Richness of ITS sequences was high (239 ITS types were detected). Genetic divergence among ITS types averaged 4% (maximum pairwise divergence was 13%). Preliminary analyses revealed nearly completely unresolved phylogenetic relationships and a lack of genetic structure among all sequences due to extensive homoplasy at multiple hypervariable sites. After correcting for this, still no clear phylogeographic structure was detected, and no pattern of isolation by distance was found on a global scale. Concomitantly, genetic differentiation among continents was marginal, whereas variation within continents was high and was mostly shared with all other continents. Similarly, no genetic structure across climate zones was detected.
  
  
  CONCLUSIONS
  The high overall diversity and wide global distribution of common ITS types in combination with the lack of phylogeographic structure suggest that intercontinental dispersal of M. aeruginosa ITS types is not rare, and that this species might have a truly cosmopolitan distribution.
authors.affiliation: Laboratory of Protistology and Aquatic Ecology, Ghent University, Ghent, Belgium.
authors.forename: Ineke
authors.initials: I
authors.lastname: van Gremberghe
authors.forename: Frederik
authors.initials: F
authors.lastname: Leliaert
authors.forename: Joachim
authors.initials: J
authors.lastname: Mergeay
authors.forename: Pieter
authors.initials: P
authors.lastname: Vanormelingen
authors.forename: Katleen
authors.initials: K
authors.lastname: Van der Gucht
authors.forename: Ann-Eline
authors.initials: AE
authors.lastname: Debeer
authors.forename: Gissell
authors.initials: G
authors.lastname: Lacerot
authors.forename: Luc
authors.initials: L
authors.lastname: De Meester
authors.forename: Wim
authors.initials: W
authors.lastname: Vyverman
mesh_terms: D001483:Base Sequence; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D030561:Databases, Nucleic Acid; D005618:Fresh Water / Q000382:microbiology*; D038622:Internationality; D046931:Microcystis / Q000235:genetics* / Q000502:physiology*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009068:Movement; D009690:Nucleic Acid Conformation; D009876:Operon / Q000235:genetics; D058974:Phylogeography; D016415:Sequence Alignment
chemical_list: D004269:DNA, Bacterial; D021901:DNA, Intergenic; D004275:DNA, Ribosomal