Comparative whole-genome analysis of clinical isolates reveals characteristic architecture of Mycobacterium tuberculosis pangenome

PLoS One. 2015 Apr 8;10(4):e0122979. doi: 10.1371/journal.pone.0122979. eCollection 2015.

Abstract

The tubercle complex consists of closely related mycobacterium species which appear to be variants of a single species. Comparative genome analysis of different strains could provide useful clues and insights into the genetic diversity of the species. We integrated genome assemblies of 96 strains from Mycobacterium tuberculosis complex (MTBC), which included 8 Indian clinical isolates sequenced and assembled in this study, to understand its pangenome architecture. We predicted genes for all the 96 strains and clustered their respective CDSs into homologous gene clusters (HGCs) to reveal a hard-core, soft-core and accessory genome component of MTBC. The hard-core (HGCs shared amongst 100% of the strains) was comprised of 2,066 gene clusters whereas the soft-core (HGCs shared amongst at least 95% of the strains) comprised of 3,374 gene clusters. The change in the core and accessory genome components when observed as a function of their size revealed that MTBC has an open pangenome. We identified 74 HGCs that were absent from reference strains H37Rv and H37Ra but were present in most of clinical isolates. We report PCR validation on 9 candidate genes depicting 7 genes completely absent from H37Rv and H37Ra whereas 2 genes shared partial homology with them accounting to probable insertion and deletion events. The pangenome approach is a promising tool for studying strain specific genetic differences occurring within species. We also suggest that since selecting appropriate target genes for typing purposes requires the expected target gene be present in all isolates being typed, therefore estimating the core-component of the species becomes a subject of prime importance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Comparative Genomic Hybridization
  • DNA, Bacterial / genetics
  • Genetic Variation*
  • Genome, Bacterial
  • Humans
  • Mycobacterium tuberculosis / classification
  • Mycobacterium tuberculosis / genetics*
  • Mycobacterium tuberculosis / pathogenicity
  • Phylogeny*
  • Tuberculosis / genetics*
  • Tuberculosis / microbiology
  • Tuberculosis / pathology

Substances

  • DNA, Bacterial

Associated data

  • SRA/SRR784917
  • SRA/SRR786188
  • SRA/SRR786373
  • SRA/SRR786397
  • SRA/SRR786667
  • SRA/SRR786668
  • SRA/SRR786669
  • SRA/SRR786670

Grants and funding

The project was funded by Council of Scientific and Industrial Research (CSIR) India through Open Source Drug Discovery (OSDD) Programme (HCP001). The Sequencing facility is supported through SIP006 and FAC002 Grant from CSIR, India and the computational analysis was performed at the CSIR centre for in-silico Biology at CSIR Institute of Genomics and Integrative Biology (IGIB).