Dataset Information

The role of selection in shaping diversity of natural M. tuberculosis populations.

ABSTRACT: Mycobacterium tuberculosis (M.tb), the cause of tuberculosis (TB), is estimated to infect a new host every second. While analyses of genetic data from natural populations of M.tb have emphasized the role of genetic drift in shaping patterns of diversity, the influence of natural selection on this successful pathogen is less well understood. We investigated the effects of natural selection on patterns of diversity in 63 globally extant genomes of M.tb and related pathogenic mycobacteria. We found evidence of strong purifying selection, with an estimated genome-wide selection coefficient equal to -9.5 × 10(-4) (95% CI -1.1 × 10(-3) to -6.8 × 10(-4)); this is several orders of magnitude higher than recent estimates for eukaryotic and prokaryotic organisms. We also identified different patterns of variation across categories of gene function. Genes involved in transport and metabolism of inorganic ions exhibited very low levels of non-synonymous polymorphism, equivalent to categories under strong purifying selection (essential and translation-associated genes). The highest levels of non-synonymous variation were seen in a group of transporter genes, likely due to either diversifying selection or local selective sweeps. In addition to selection, we identified other important influences on M.tb genetic diversity, such as a 25-fold expansion of global M.tb populations coincident with explosive growth in human populations (estimated timing 1684 C.E., 95% CI 1620-1713 C.E.). These results emphasize the parallel demographic histories of this obligate pathogen and its human host, and suggest that the dominant effect of selection on M.tb is removal of novel variants, with exceptions in an interesting group of genes involved in transportation and defense. We speculate that the hostile environment within a host imposes strict demands on M.tb physiology, and thus a substantial fitness cost for most new mutations. In this respect, obligate bacterial pathogens may differ from other host-associated microbes such as symbionts.

SUBMITTER: Pepperell CS

PROVIDER: S-EPMC3744410 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

The role of selection in shaping diversity of natural M. tuberculosis populations.

Pepperell Caitlin S CS Casto Amanda M AM Kitchen Andrew A Granka Julie M JM Cornejo Omar E OE Holmes Edward C EC Birren Bruce B Galagan James J Feldman Marcus W MW

PLoS pathogens 20130815 8

Mycobacterium tuberculosis (M.tb), the cause of tuberculosis (TB), is estimated to infect a new host every second. While analyses of genetic data from natural populations of M.tb have emphasized the role of genetic drift in shaping patterns of diversity, the influence of natural selection on this successful pathogen is less well understood. We investigated the effects of natural selection on patterns of diversity in 63 globally extant genomes of M.tb and related pathogenic mycobacteria. We found ...[more]

PMID: 23966858

Similar Datasets

Project description:Rational drug design creates innovative therapeutics based on knowledge of the biological target to provide more effective and responsible therapeutics. Chagas disease, endemic throughout Latin America, is caused by Trypanosoma cruzi, a protozoan parasite. Current therapeutics are problematic with widespread calls for new approaches. Researchers are using rational drug design for Chagas disease and one target receiving considerable attention is the T. cruzi trans-sialidase protein (TcTS). In T. cruzi, trans-sialidase catalyzes the transfer of sialic acid from a mammalian host to coat the parasite surface membrane and avoid immuno-detection. However, the role of TcTS in pathology variance among and within genetic variants of the parasite is not well understood despite numerous studies. Previous studies reported the crystalline structure of TcTS and the TS protein structure in other trypanosomes where the enzyme is often inactive. However, no study has examined the role of natural selection in genetic variation in TcTS. To understand the role of natural selection in TcTS DNA sequence and protein variation, we examined a 471 bp portion of the TcTS gene from 48 T. cruzi samples isolated from insect vectors. Because there may be multiple parasite genotypes infecting one insect and there are multiple copies of TcTS per parasite genome, all 48 sequences had multiple polymorphic bases. To resolve these polymorphisms, we examined cloned sequences from two insect vectors. The data are analyzed to understand the role of natural selection in shaping genetic variation in TcTS and interpreted in light of the possible role of TcTS as a drug target. The analysis highlights negative or purifying selection on three amino acids previously shown to be important in TcTS transfer activity. One amino acid in particular, Tyr342, is a strong candidate for a drug target because it is under negative selection and amino acid substitutions inactivate TcTS transfer activity. AUTHOR SUMMARY: Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and transmitted to humans and other mammals primarily by Triatomine insects. Being endemic in many South and Central American countries and affecting millions of people the need for new more effective and safe therapies is evident. Here, we examine genetic variation and natural selection on DNA (471 bp) and amino acid (157 aa) sequence data of the T. cruzi trans-sialdiase (TcTS) protein, often suggested as a candidate for rational drug design. In our surveyed region of the protein there were five amino acid residues that have been shown to be integral to the function of TcTS. We found that three were under strong negative selection making them ideal candidates for drug design; however, one was under balancing selection and should be avoided as a drug target. Our study provides new information into identifying potential targets for a new Chagas drug.

Dataset Information

The role of selection in shaping diversity of natural M. tuberculosis populations.

Publications

The role of selection in shaping diversity of natural M. tuberculosis populations.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets