Abstract
The field of microbiology was established in the 17th 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.
Highlights
Cell and polar shape ellipsoidal with polar nodule truncateellipsoidal with polar thickening truncate-ellipsoidal with polar thickening
Using LM on the 13 strains (Supplementary Table 1), two Glaucocystis species were identified based on the traditional taxonomic system[19,23,24] (Supplementary Table 2): G. nostochinearum and G. oocystiformis Prescott (1944)[23]
We found differences that could contribute to species delineation within G. nostochinearum in our new taxonomic system (Table 1; Fig. 1; Supplementary Figs 1,2; Supplementary Note)
Summary
Cell and polar shape ellipsoidal with polar nodule truncateellipsoidal with polar thickening truncate-ellipsoidal with polar thickening. 17–27 μm long truncate-ellipsoidal without polar thickening ca. 18–27 μm long ellipsoidal without polar ellipsoidal without nodule polar nodule ca. 100–300 nm type B absent ND present SAG 16.98. On the other hand, scanning electron microscopy (SEM) can reveal the characteristics of the entire cell surface, globally, but conventional SEM does not have sufficiently high resolution to observe ultrastructures in detail[10,11]. Two types of new-generation EM, ultra-high-resolution (UHR) field-emission (FE)-SEM and ultra-high-voltage electron microscopy (UHVEM), have introduced a new paradigm in the field of biology[10,11,12,13,14]. In some recent studies of microalgal and protozoan taxonomy, the utility of molecular approaches continues to be overemphasised[15,16,17,18]
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