Delineation of six species of the primitive algal genus Glaucocystis based on in situ ultrastructural characteristics.

The field of microbiology was established in the 17(th) century upon the discovery of microorganisms by Antonie van Leeuwenhoek using a single-lens microscope. Now, the detailed ultrastructures of microorganisms can be elucidated in situ using three-dimensional electron microscopy. Since the availability of electron microscopy, the taxonomy of microscopic organisms has entered a new era. Here, we established a new taxonomic system of the primitive algal genus Glaucocystis (Glaucophyta) using a new-generation electron microscopic methodology: ultra-high-voltage electron microscopy (UHVEM) and field-emission scanning electron microscopy (FE-SEM). Various globally distributed Glaucocystis strains were delineated into six species, based on differences in in situ ultrastructural features of the protoplast periphery under UHVEM tomography and in the mother cell wall by FE-SEM, as well as differences in the light microscopic characteristics and molecular phylogenetic results. The present work on Glaucocystis provides a model case of new-generation taxonomy.

A new type of 3-D peripheral ultrastructure in Glaucocystis (Glaucocystales, Glaucophyta) as revealed by ultra-high voltage electron microscopy.

The coccoid glaucophyte genus Glaucocystis is characterized by having a thick cell wall, which has to date prohibited examination of the native ultrastructural features of the protoplast periphery. Recently, however, the three-dimensional (3-D) ultrastructure of the protoplast periphery was revealed in two divergent Glaucocystis species, with the world's most powerful ultra-high voltage electron microscope (UHVEM). The two species exhibit morphological diversity in terms of their 3-D ultrastructural features. However, these two types do not seem to encompass actual ultrastructural diversity in the genetically diverse genus Glaucocystis. Here, we report a new type of peripheral 3-D ultrastructure resolved in "G. incrassata" SAG 229-2 cells by 3-D modeling based on UHVEM tomography using high-pressure freezing and freeze-substitution fixation. The plasma membrane and underlying flattened vesicles in "G. incrassata" SAG 229-2 exhibited grooves at intervals of 200-600 nm, and the flattened vesicles often overlapped one another at the protoplast periphery. This 3-D ultrastructure differs from those of the two types previously reported in other species of Glaucocystis. The possibility of classification of Glaucocystis species based on the 3-D ultrastructure of the protoplast periphery is discussed.