The phylogeny of unicellular, extremely halotolerant cyanobacteria

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 micron. 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.

Phylogenetic and taxonomic delimitation of the cyanobacterial genusAphanotheceand description ofAnathece gen. nov.

“…Garcia-Pichel et al (1998) and Margheri et al (1999) designated similar halophilic types without gelatinous envelopes as Halothece (validated by Margheri et al, 2008) and 'Euhalothece'. The ultrastructure of both is similar to Aphanothece sensu stricto, but a final evaluation of these genera will need to be determined from molecular data (Figs 1, 2) and ecology.…”

Determining the specific microbial populations and their spatial distribution within the stromatolite ecosystem of Shark Bay

“…mirrors the composition of other hypersaline ecosystems (Garcia-Pichel et al, 1998;Nubel et al, 2000).…”

Diversity and Distribution in Hypersaline Microbial Mats of Bacteria Related to Chloroflexus spp

“…Very similarly, cyanobacteria in the same hypersaline microbial mats were recently found to form several phylogenetic lineages only distantly related to their freshwater morphological counterparts (9,24,26). In different habitats, analogous ecological niches may be occupied by different microorganisms, each adapted to the respective physicochemical conditions.…”

“…Microbial mats were sampled in June 1999 from evaporation ponds 4 to 7 of the saltern in Guerrero Negro (6). For enrichments of anoxygenic phototrophic bacteria, a medium for cyanobacteria (9) , and resazurin (0.0001%, wt/vol). The medium was boiled to drive out dissolved oxygen, and 10 ml was aliquoted into 20-ml screw-cap tubes under a stream of nitrogen.…”