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Category: Microbial Genetics and Molecular Biology
Mycobacterial Pathogenomics and Evolution, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818845/9781555818838_Chap02-1.gif /docserver/preview/fulltext/10.1128/9781555818845/9781555818838_Chap02-2.gifAbstract:
Mycobacteria are widespread microorganisms characterized by the high G+C content of their genomes and a lipid-rich cell envelope. The genus Mycobacterium represents the only entity within the family Mycobacteriaceae, which belongs to the order Actinomycetales and the phylum Actinobacteria ( 1 ). Whereas the great majority of the ∼130 described species in the genus are harmless environmental saprophytes, some mycobacteria have evolved to be major pathogens. With the exception of Mycobacterium abscessus, which is recognized as an emerging human pathogen in cystic fibrosis patients ( 2 – 4 ), the pathogenic species mainly belong to the slowly growing mycobacteria and comprise well-known human pathogens such as Mycobacterium tuberculosis, Mycobacterium leprae, and Mycobacterium ulcerans as well as confirmed animal pathogens such as Mycobacterium bovis, Mycobacterium avium paratuberculosis, and Mycobacterium marinum ( 5 ).
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Proposed scenario of pathoadaptation of tubercle bacilli from a hypothetical mycobacterial common ancestor (most recent common ancestor, MRCA), adapted from reference 49 . In the proposed evolutionary pathway M. tuberculosis strains gain specific functions (via horizontal gene transfer, recombination, mutation and/or gene loss, etc.), which allow them to better replicate and persist under the environment and temperature conditions of a niche such as human macrophages. It is plausible that the pathogenomic adaptation at some stage involved smooth tubercle bacilli/M. canettii, which show a broader environmental adaptability and a genetically much larger diversity than the M. tuberculosis senso stricto strains ( 35 ).
Network phylogeny inferred among the five M. canettii strains subjected to complete genome sequence analysis and 39 selected genome sequences from members of the classical M. tuberculosis complex by NeighborNet analysis, based on pairwise alignments of whole-genome SNP data, which in part are also listed in the lower right portion of the figure. The color code and the naming of different phylogenetic lineages within the M. tuberculosis complex refer to the nomenclature used in reference 59 .
Working model of the type VII secretion apparatus adapted from reference 121 . Schematic representation of the core components and their interactions. Various ESX components belonging to different protein families are represented by different colors: orange, amino-terminal transmembrane protein; violet, amino-terminal transmembrane ATPase; green, integral membrane protein; red, mycosin (subtilisin-like serine protease); pink, AAA+ ATPase. Esx secreted substrates, PE and PPE proteins, as well as ESX-1-associated Esp proteins are also represented. Note that the channel drawn in the mycomembrane refers to a hypothetical protein, whose existence has not been experimentally demonstrated, and that the drawing of the mycomembrane follows a schematic representation of reference 17 .