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Archives of Microbiology

, Volume 169, Issue 6, pp 469–482 | Cite as

The phylogeny of unicellular, extremely halotolerant cyanobacteria

  • F. Garcia-Pichel
  • Ulrich Nübel
  • Gerard Muyzer
Original paper

Abstract

We examined the morphology, physiology, and 16S rRNA gene sequences of three culture collection strains and of ten novel isolates of unicellular cyanobacteria from hypersaline environments. The strains were morphologically diverse, with average cell widths ranging from 2.8 to 10.3 μm. There were single-celled, colonial, and baeocyte-forming strains. However, morphological traits were markedly variable with culture conditions. In contrast, all strains displayed extreme halotolerance (growing close to optimally at above 12% salinity); all were obligately marine, euryhaline, and moderately thermophilic; and all shared a suite of chemotaxonomic markers including phycobilins, carotenoids, and mycosporine-like amino acids. 16S rRNA gene sequence analysis indicated that the strains were related to each other. Sequence similarity analysis placed the strains in a monophyletic cluster (which we named the Halothece cluster) apart from all cultured or uncultured, not extremely halotolerant cyanobacteria whose 16S rRNA gene sequences are available in public nucleotide sequence databases. This represents the first case in which a phylogenetically coherent group of cyanobacteria can be defined on the basis of physiology. The Halothece cluster contained two subclusters that may be divergent at the generic level, one encompassing 12 strains (spanning 5% 16S rRNA gene sequence divergence and named the Euhalothece subcluster), and a single deep-branching isolate. Phenotypic characterization of the isolates, including morphological, physiological, and chemotaxonomic traits, did not distinguish these subclusters and only weakly suggested the existence of two separate clades, one encompassing strains of small cell size (cell width < 5 m) and another one encompassing strains of larger cell size.

Key words Cyanobacteria Halophiles Halotolerance Hypersaline environments Phylogeny Taxonomy Microbial mats 

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Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • F. Garcia-Pichel
    • 1
  • Ulrich Nübel
    • 1
  • Gerard Muyzer
    • 1
  1. 1.Max-Planck-Institut for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen, Germany e-mail: fgarcia@mpi-bremen.de Tel. +49-421-2028-838; Fax +49-421-2028-580DE

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