Mathematical modelling of Mycobacterium tuberculosis VNTR loci estimates a very slow mutation rate for the repeats

Andrew Grant, Catherine Arnold, Nicola Thorne, Saheer Gharbia, Anthony Underwood*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)


Minisatellites are highly variable tandem repeats used for over 20 years in humans for DNA fingerprinting. In prokaryotes fingerprinting techniques exploiting VNTR (variable number of tandem repeats) polymorphisms have become widely used recently in bacterial typing. However although many investigations into the mechanisms underlying minisatellite variation in humans have been performed, relatively little is known about the processes that mediate bacterial minisatellite polymorphism. An understanding of this is important since it will influence how the results from VNTR experiments are interpreted. The minisatellites of Mycobacterium tuberculosis are well characterized since they are some of the few polymorphic loci in what is otherwise a very homogeneous organism. Using VNTR results from a well-defined and characterized set of M. tuberculosis strains we show that the repeats at a locus are likely to evolve by stepwise contraction or expansion in the number of repeats. A stochastic continuous-time population mathematical model was developed to simulate the evolution of the repeats. This allowed estimation of the tendency of the repeats to increase or decrease and the rate at which they change. The majority of loci tend to lose rather than gain repeats. All of the loci mutate extremely slowly, with an average rate of 2.3 × 10-8, which is 350 times slower than that of a set of VNTR repeats with similar diversity observed experimentally in Escherichia coli. This suggests that the VNTR profile of a strain of M. tuberculosis will be indicative of its clonal lineage and will be unlikely to vary in epidemiologically-related strains.

Original languageEnglish
Pages (from-to)565-574
Number of pages10
JournalJournal of Molecular Evolution
Issue number6
Publication statusPublished - Jun 2008

Bibliographical note

Funding Information:
This work was supported in part by a PhD studentship funded by Biotage AB.


  • Mathematical modelling
  • Mycobacterium tuberculosis
  • Stochastic processes
  • VNTR


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