The halotolerance and phylogeny of cyanobacteria with tightly coiled trichomes (Spirulina Turpin) and the description of Halospirulina tapeticola gen. nov., sp nov.

The morphologies, halotolerances, temperature requirements, pigment composi tions and 16S rRNA gene sequences of five culture collection strains and si x novel isolates of cyanobacteria with helical, tightly coiled trichomes we re investigated. All strains were very similar morphologically and could be assigned to the genus Spirulina (or section Euspirulina sensu Geitler), ac cording to traditional classification. However, the isolates showed signifi cantly different requirements for salinity and temperature, which were in a ccordance with their respective environmental origins. The genetic divergen ce among the strains investigated was large. The results indicate the drast ic underestimation of the physiological and phylogenetic diversity of these cyanobacteria by the current morphology-based classification and the clear need for new taxa. Three of the isolates originated from hypersaline water s and were similar with respect to their high halotolerance, broad euryhali nity and elevated temperature tolerance. By phylogenetic analyses, they wer e placed in a tight monophyletic cluster apart from all other cyanobacteria . Thus it is proposed to reclassify highly halotolerant cyanobacteria with tightly coiled trichomes in Halospirulina gen. nov., with the type species Halospirulina tapeticola sp. nov.