An electron microscopic study of microorganisms: from influenza virus to deep-sea microorganisms

Abstract

Three topics from electron microscopic studies of microorganisms carried out in my laboratory in recent ten years are described. 1) Influenza A virus was observed in water by an ice-embedding method using phase contrast electron microscopy developed in Japan. Virions appeared as spherical or elongated particles consisting of spikes, an envelope, and a core with high contrast. 2) A new term the "structome" was introduced and defined as "the quantitative and three-dimensional structural information of a whole cell at electron microscopic level." We performed structome analyses of Saccharomyces cerevisiae by using freeze-substitution and serial ultrathin sectioning electron microscopy. We found that there were one to four mitochondria and about 195,000 ribosomes in a cell. 3) In the deep-sea off the coast of Japan, we discovered a unique microorganism appearing to have cellular features intermediate between prokaryotes and eukaryotes. The organism, named as the Myojin parakaryote, was two orders of magnitude larger than a typical bacterium and had a large "nucleoid", surrounded by a single layered "nucleoid membrane", and bacteria-like "endosymbionts", but it lacked mitochondria. This organism exemplifies a potential evolutionary path between prokaryotes and eukaryotes, and the presence of the organism supports the endosymbiotic theory for the origin of mitochondria and the karyogenetic hypothesis for the origin of the nucleus. These studies show that the electron microscopy is a powerful tool for studying a wide range of problems of microorganisms.

A Method for Obtaining Serial Ultrathin Sections of Microorganisms in Transmission Electron Microscopy

“…The specimens used in this study were microorganisms, rapidly frozen with propane in liquid nitrogen, freeze substituted in acetone containing 2% osmium tetroxide, and embedded in epoxy resin 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18 .…”

“…Further, structome analysis led to the discovery of a new organism; Parakaryon myojinensis was found in the deep sea off the coast of Japan, whose cell structure were an intermediate between those of prokaryotes and eukaryotes 12,13,14,15 . At present, serial ultrathin sectioning technique is considered to be so difficult that it would take a long time to master.…”

High-voltage electron microscopy tomography and structome analysis of unique spiral bacteria from the deep sea

“…In 2012, we discovered a unique microorganism that has intermediate cellular structures between prokaryotes and eukaryotes, and named it the 'Myojin parakaryote' after the discovery location and its intermediate morphology [1]. From our observations using ultrathin sections of freezesubstituted specimens with electron microscopy, it became apparent that there are many other strange microorganisms in the deep sea [2,3]. Among them, unique spiral bacteria were conspicuous and abundant in the deep-sea specimens.…”

Good Ultrastructural Preservation of Human Tissues and Cultured Cells by Glutaraldehyde Fixation, Sandwich Freezing, and Freeze-Substitution

“…Chemical fixation by glutaraldehyde, sandwichfreezing, and freeze-substitution of microorganisms (chemical fixation-freeze substitution, CF-FS) was found to better preserve the ultrastructure of cells compared to CF-CD (Yamaguchi et al 2005a(Yamaguchi et al , 2011b. The CF-FS has been applied to observe ultrastructure of not only microorganisms but also cultured cells with good results (Yamaguchi et al 2012, 2016a, b, 2017, Yamada et al 2014, Yamaguchi and Worman 2014 et al. 2015, Yamaguchi 2015, Aoki et al 2017, Hirao et al 2018.…”

“…The CF-FS has been applied to observe ultrastructure of not only microorganisms but also cultured cells with good results (Yamaguchi et al 2012, 2016a, b, 2017, Yamada et al 2014, Yamaguchi and Worman 2014 et al. 2015, Yamaguchi 2015, Aoki et al 2017, Hirao et al 2018.…”