AUTHOR=Yamada Hiroyuki , Chikamatsu Kinuyo , Aono Akio , Murata Kazuyoshi , Miyazaki Naoyuki , Kayama Yoko , Bhatt Apoorva , Fujiwara Nagatoshi , Maeda Shinji , Mitarai Satoshi 

TITLE=Fundamental Cell Morphologies Examined With Cryo-TEM of the Species in the Novel Five Genera Robustly Correlate With New Classification in Family Mycobacteriaceae

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.562395

DOI=10.3389/fmicb.2020.562395

ISSN=1664-302X

ABSTRACT=<p>A recent study proposed the novel classification of the family <italic>Mycobacteriaceae</italic> based on the genome analysis of core proteins in 150 <italic>Mycobacterium</italic> species. The results from these analyses supported the existence of five distinct monophyletic groups within the genus <italic>Mycobacterium</italic>. That is, <italic>Mycobacterium</italic> has been divided into two novel genera for rapid grower <italic>Mycobacteroides</italic> and <italic>Mycolicibacterium</italic>, and into three genera for slow grower <italic>Mycolicibacter</italic>, <italic>Mycolicibacillus</italic>, and an emended genus <italic>Mycobacterium</italic>, which include all the major human pathogens. Here, cryo-TEM examinations of 1,816 cells of 31 species (34 strains) belonging to the five novel genera were performed. The fundamental morphological properties of every single cell, such as cell diameter, cell length, cell perimeter, cell circularity, and aspect ratio were measured and compared between these genera. In 50 comparisons on the five parameters between any two genera, only five comparisons showed “non-significant” differences. That is, there are non-significant differences between slow grower genus <italic>Mycolicibacillus</italic> and genus <italic>Mycobacterium</italic> in average cell diameter (<italic>p</italic> = 0.15), between rapid grower genus <italic>Mycobacteroides</italic> and slow grower genus <italic>Mycobacterium</italic> in average cell length (<italic>p</italic> &gt; 0.24), between genus <italic>Mycobacteroides</italic> and genus <italic>Mycobacterium</italic> (<italic>p</italic> &gt; 0.68) and between genus <italic>Mycolicibacter</italic> and genus <italic>Mycolicibacillus</italic> (<italic>p</italic> &gt; 0.11) in average cell perimeter, and between genus <italic>Mycolicibacterium</italic> and genus <italic>Mycobacterium</italic> in circularity (<italic>p</italic> &gt; 0.73). The other 45 comparisons showed significant differences between the genera. Genus <italic>Mycobacteroides</italic> showed the longest average cell diameter, whereas the genus <italic>Mycolicibacter</italic> showed the shortest average diameter. Genus <italic>Mycolicibacterium</italic> showed the most extended average cell length, perimeter, and aspect ratio, whereas the genus <italic>Mycolicibacillus</italic> showed the shortest average cell length, perimeter, and aspect ratio. Genus <italic>Mycolicibacillus</italic> showed the highest average cell circularity, whereas genus <italic>Mycobacterium</italic> showed the lowest average cell circularity. These fundamental morphological data strongly support the new classification in the family <italic>Mycobacteriaceae</italic>, and this classification is rational and effective in the study of the members of the family <italic>Mycobacteriaceae</italic>. Because both the genus <italic>Mycolicibacterium</italic> and the genus <italic>Mycobacterium</italic> contain many species and showed larger significant standard deviations in every parameter, these genera may be divided into novel genera which show common genotype and phenotypes in morphology and pathogenicity.</p>