Phylogenomics reveal that Mycobacterium kansasii subtypes are species-level lineages. Description of Mycobacterium pseudokansasii sp. nov., Mycobacterium innocens sp. nov. and Mycobacterium attenuatum sp. nov.

ABSTRACT

Among the species Mycobacterium kansasii, seven subtypes have been previously reported based on the PCR and the restriction fragment length polymorphism of the gene hsp65. Here, we used whole-genome sequencing to refine M. kansasii taxonomy and correct multiple inconsistencies. Average nucleotide identity (ANI) values between M. kansasii subtypes ranged from 88.4 to 94.2 %, lower than the accepted 95-96 % cut-off for species delineation. In addition, Mycobacterium gastri was closer to the M. kansasii subtypes 1, 2, 3, 4 and 5 than M. kansasii subtype 6. The recently described species Mycobacterium persicum shared 99.77 % ANI with M. kansasii subtype 2. Consistent with the ANI results, the digital DNA-DNA hybridization value was below the 70 % threshold for species delineation between subtypes and above it within subtypes as well as between subtype 2 and M. persicum. Furthermore, core-genome phylogeny confirmed the current M. kansasii species to be polyphyletic. Hence, we propose (i) Mycobacterium pseudokansasii sp. nov., replacing subtype 3, with the type strain MK142T(=CCUG 72128T=DSM 107152T), (ii) Mycobacterium innocens sp. nov., replacing subtype 5, with the type strain MK13T (=CCUG 72126T=DSM 107161T), and (iii) Mycobacterium attenuatum sp. nov., replacing subtype 6, with the type strain MK41T(=CCUG 72127T=DSM 107153T). Subtype 4 represents a new species-level lineage based on the genomic data but no strain was available. No genome sequence or strain was available for subtype 7. The proposed nomenclature will facilitate the identification of the most pathogenic subtype 1 as M. kansasii by clinicians while the new species names suggest the attenuated pathogenicity of the other subtypes.