Toxin-antitoxin systems shows variability among Mycobacterium tuberculosis lineages

The toxin-antitoxin (TA) systems are operons involved in the formation of persistent cells and in stress situations in microorganism. TA systems are widely distributed in Mycobacterium tuberculosis (MTB). The objective of this study was to determine the distribution and variability of protein sequences of TA systems in seven MTB lineages. Protein prediction on 73 genomes of different lineage was made using Prodigal, and profile hidden Markov models (PHMMs) of 225 reference TA proteins were constructed with HMMER. An homology search was made comparing the predicted proteins to PHMMs. Consecutive proteins that matched PHMMs (forming an operon) were selected. Thereafter, clustering of orthologous genes was made for further mutation scanning through multiple alignments. All proteins found belong to TA types II and IV, and 45 proteins were found completely conserved. Six uncharacterized antitoxins homologous to VapB11, VapB5, VapB45, VapB13, ParD1 and RelB were found. Multiple alignments revealed differences among lineages with specific mutations suitable for genotyping. Significant changes in amino acid sequences caused by frameshift mutations were found in 46 TA proteins.