知花 博治

© 2018 The Japan Mendel Society. 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.

深在性真菌症に対する適応薬は4系統のみであり、耐性菌の増加が大きな問題となっている。抗真菌薬の市場規模は今後も拡大が見込まれているにもかかわらず、新規作用機序をもつ抗真菌薬は抗ニューモシスチス薬を除き15年以上承認されていない。抗真菌薬の開発の困難さは、分子系統学的に真菌が動物と近縁であり、分子レベルでの構造が類似した物質が多いことに起因している。そこで我々は、副作用のリスクを回避しながら、多岐にわたる病原真菌種に対応できる薬剤開発の困難さを克服するための技術開発に取り組んでいる。(著者抄録)