title: Cyanobacterial diversity in natural and artificial microbial mats of Lake Fryxell (McMurdo Dry Valleys, Antarctica): a morphological and molecular approach.
abstract: Currently, there is no consensus concerning the geographic distribution and extent of endemism in Antarctic cyanobacteria. In this paper we describe the phenotypic and genotypic diversity of cyanobacteria in a field microbial mat sample from Lake Fryxell and in an artificial cold-adapted sample cultured in a benthic gradient chamber (BGC) by using an inoculum from the same mat. Light microscopy and molecular tools, including 16S rRNA gene clone libraries, denaturing gradient gel electrophoresis, and sequencing, were used. For the first time in the study of cyanobacterial diversity of environmental samples, internal transcribed spacer (ITS) sequences were retrieved and analyzed to complement the information obtained from the 16S rRNA gene. Microscopy allowed eight morphotypes to be identified, only one of which is likely to be an Antarctic endemic morphotype. Molecular analysis, however, revealed an entirely different pattern. A much higher number of phylotypes (15 phylotypes) was found, but no sequences from Nodularia and Hydrocoryne, as observed by microscopy, were retrieved. The 16S rRNA gene sequences determined in this study were distributed in 11 phylogenetic lineages, 3 of which were exclusively Antarctic and 2 of which were novel. Collectively, these Antarctic sequences together with all the other polar sequences were distributed in 22 lineages, 9 of which were exclusively Antarctic, including the 2 novel lineages observed in this study. The cultured BGC mat had lower diversity than the field mat. However, the two samples shared three morphotypes and three phylotypes. Moreover, the BGC mat allowed enrichment of one additional phylotype. ITS sequence analysis revealed a complex signal that was difficult to interpret. Finally, this study provided evidence of molecular diversity of cyanobacteria in Antarctica that is much greater than the diversity currently known based on traditional microscopic analysis. Furthermore, Antarctic endemic species were more abundant than was estimated on the basis of morphological features. Decisive arguments concerning the global geographic distribution of cyanobacteria should therefore incorporate data obtained with the molecular tools described here.
authors.affiliation: Laboratoire d'Algologie, de Mycologie et de Systématique Expérimentale, Institut de Botanique B22, Université de Liège, B-4000 Liège, Belgium.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Taton
authors.forename: Stana
authors.initials: S
authors.lastname: Grubisic
authors.forename: Evelyne
authors.initials: E
authors.lastname: Brambilla
authors.forename: Rutger
authors.initials: R
authors.lastname: De Wit
authors.forename: Annick
authors.initials: A
authors.lastname: Wilmotte
mesh_terms: D000064:Acclimatization; D000864:Antarctic Regions; D001483:Base Sequence; D003001:Cloning, Molecular; D003080:Cold Temperature; D000458:Cyanobacteria / Q000145:classification* / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D017931:DNA Primers; D004275:DNA, Ribosomal / Q000235:genetics; D005618:Fresh Water / Q000382:microbiology*; D015723:Gene Library; D010802:Phylogeny; D015183:Restriction Mapping
chemical_list: D017931:DNA Primers; D004275:DNA, Ribosomal