Variability assessment of PE_PGRS genes and DNA repair, replication, and recombination genes in Mycobacterium tuberculosis

Abstract

The variability assessment of PE/PPE genes, as well as of DNA repair, replication, and recombination system genes may drive the concept of mechanisms of Mycobacterium tuberculosis evolution and adaptation.The aim is to study the variability of PE_PGRS genes, 3R-system genes (DNA repair, recombination, and replication) to assess the mechanisms of evolutionary changes in M. tuberculosis.Whole genome sequencing of M. tuberculosis 11502 (the Beijing genotype subtype B0/W148 cluster 100-32), M. tuberculosis 5005 (the Beijing genotype subtype B0/W148), M. tuberculosis 4860 (the LAM genotype) strains was performed. They were isolated from patients with newly diagnosed pulmonary tuberculosis. Genomes were uploaded to the GanBank, NCBI: M. tuberculosis 11502 – access code: CP070338.1, M. tuberculosis 5005 – access code: CP053092.1, M. tuberculosis 4860 – access code: CP049108.1. A reference genome (M. tuberculosis H37Rv; NC_000962.3) was used for genetic analysis. In the M. tuberculosis 11502 genome, 44.4 ± 6.8 % of genes (24 genes out of 54) were revealed in the mutations related to the 3R system, while in M. tuberculosis 4860– 29.6 ± 6.2 % (16 genes out of 54). In the 3R system genes, a slight shift of mutations towards replacement by adenine and thymine was revealed, while the entire genome of M. tuberculosis 11502 (compared to M. tuberculosis H37Rv) demonstrated mutations, resulting in a slight accumulation of G + C. Mutations in the 3R system genes may lead to the suboptimal activity of proteins responsible for the DNA-repair, resulting in the upsurge of mutation frequency and promoting adaptive evolution. PE_PGRS genes in the genome of M. tuberculosis 11502, 4860, and 5005 exhibited a high variability and their variability diverged among different members of this gene family. A high level of tetranucleotides CGGC was found in the majority of PE_PGRS family genes, where their proportion varied from 2.11 to 8.42 %, while an average proportion of CGGC in the M. tuberculosis genome was 1.62 %. Some genes in the M. tuberculosis genome were detected to carry no tetranucleotides CGGC (Rv0011, Rv0100, Rv0460, Rv0616A, Rv0691A, Rv0722, Rv0863, Rv0909, Rv1038c, Rv1197, Rv2347c, Rv2452c, and Rv3330c). The DNA conformation analysis at the mutation sites in the genes, associated with resistance to anti-tuberculosis drugs, showed that the secondary DNA structures were mainly formed by nucleotides CGGC, GCGC, GGG, GGGG, CTGC, and mutations occurred, predominantly, at the sites of forming secondary DNA structures (hairpins) where the redistribution of energy and charges can influence the accuracy of replication and result in replication errors and a mutation event. A number of additional factors can influence the probability of a mutation event. These are the factors that can neutralize the energy changes in the DNA secondary structures, and can affect the accuracy of DNA-repair and replication (mutations in the gyrA gene, in the 3R-system genes).