2018 年 83 巻 3 号 p. 337-342
Structome analysis, quantitative and three-dimensional structural analysis of a whole cell at the electron microscopic level, is a useful tool for identification of unknown microorganisms that cannot be cultured. In 2012, we discovered a unique microorganism with a cell structure intermediate between those of prokaryotes and eukaryotes from the deep sea off the coast of Japan and named it Parakaryon myojinensis. We also reported another unique bacterium found in the same place that we named as Myojin spiral bacteria. Here, we report the third unique bacteria we discovered by structome analysis and 3D reconstruction using serial ultrathin sectioning of freeze-substituted specimens from the same place. The bacteria showed elongated flattened cell bodies with uneven surfaces. The cells consisted of outer amorphous materials, cell wall, cytoplasmic membrane, ribosomes, fibrous materials, and vacuoles. They had a total length of 1.82±0.40 µm, a total volume of 0.37±0.09 µm3, and had 1150±370 ribosomes within a cell; the density of the ribosomes in the cytoplasm was 312±41 per 0.1fL. Each bacterium showed different shapes but appears to belong to a single species because they have similar size and volume, have similar internal structure, inhabit a confined area, and have similar ribosome density in the cytoplasm. We named it the ‘Myojin amorphous bacteria’ after the location of discovery and its morphology. This is the first report on the existence of amorphous bacteria.
