Origins of a 350-kilobase genomic duplication in Mycobacterium tuberculosis and its impact on virulence.
In the present study, we have investigated the evolution and impact on virulence of a 350-kb genomic duplication present in the most recently evolved members of the Mycobacterium tuberculosis East Asian lineage. In a mouse model of infection, comparing HN878 subclones HN878-27 (no duplication) and HN878-45 (with the 350-kb duplication) revealed that the latter is impaired for in vivo growth during the initial 3 weeks of infection. Furthermore, the median survival time of mice infected with isolate HN878-45 is significantly longer (77 days) than that of mice infected with HN878-27. Whole-genome sequencing of both isolates failed to reveal any mutational events other than the duplication that could account for such a substantial difference in virulence. Although we and others had previously speculated that the 350-kb duplication arose in response to some form of host-applied selective pressure (P. Domenech, G. S. Kolly, L. Leon-Solis, A. Fallow, M. B. Reed, J. Bacteriol. 192: 4562-4570, 2010, and B. Weiner, J. Gomez, T. C. Victor, R. M. Warren, A. Sloutsky, B. B. Plikaytis, J. E. Posey, P. D. van Helden, N. C. Gey van Pittius, M. Koehrsen, P. Sisk, C. Stolte, J. White, S. Gagneux, B. Birren, D. Hung, M. Murray, J. Galagan, PLoS One 7: e26038, 2012), here we show that this large chromosomal amplification event is very rapidly selected within standard in vitro broth cultures in a range of isolates. Indeed, subclones harboring the duplication were detectable after just five rounds of in vitro passage. In contrast, the duplication appears to be highly unstable in vivo and is negatively selected during the later stages of infection in mice. We believe that the rapid in vitro evolution of M. tuberculosis is an underappreciated aspect of its biology that is often ignored, despite the fact that it has the potential to confound the data and conclusions arising from comparative studies of isolates at both the genotypic and phenotypic levels.
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Pilar
P
Domenech
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Anya
A
Rog
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Jalal-ud-din
JU
Moolji
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Nicolas
N
Radomski
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Ashley
A
Fallow
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Lizbel
L
Leon-Solis
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada.
Julia
J
Bowes
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada McGill International TB Centre, Montreal, Quebec, Canada.
Marcel A
MA
Behr
Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada McGill International TB Centre, Montreal, Quebec, Canada michael.reed@mcgill.ca.
Michael B
MB
Reed
D000818:Animals; D005260:Female; D020440:Gene Duplication; D015964:Gene Expression Regulation, Bacterial; D051379:Mice; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity*; D014376:Tuberculosis / Q000382:microbiology*; D014774:Virulence