Cytomorphology of six halotolerant coccoid cyanobacteria using DAPI fluorescent and transmission electron microscopy, compared with molecular data

Cytomorphological characters of six strains of unicellular cyanophytes, all belonging to Euhalothece/Halothece group in the sense of GARCIA-PICHEL et al. (1998), but of different hypersaline origin, have been studied using DAPI fluorescent staining and light and transmission electron microscopy. They can be divided into two clades, which are well separated according to phenotypic taxonomy (morphology, cytology and ultrastructure). The first group (four strains) could be included in the subcluster Euhalothece (on the generic level, but not yet validly described). Broad oval cells of ca 4-6 mu m breadth with indistinct chromatoplasm, net like nucleoids and parallel lengthwise arranged thylakoids often in fascicles are characteristic for this group. The second subcluster should be classified into another genus because of oblong or rod shaped cells of smaller size (cca 2-4 mu m wide), peripheral chromatoplasm (position of mostly lengthwise parietal thylakoids) and more or less compact nucleoid. These strains belong into the vicinity of the genus Cyanobium.