Abstract
The Mycobacterium tuberculosis complex causes tuberculosis (TB) in humans and other animal species, but Mycobacterium tuberculosis has a distinct host preference to humans. The present study aimed to determine whether a bovine M. tb strain 1458 has evolved some genetic properties in their genome that might be associated with their bovine adaptation. The genome of the M. tb strain 1458 was sequenced and subjected to an extensive comparative genomic analysis. A phylogenetic analysis showed that strain 1458 is most closely related to a Chinese M. tb strain, CCDC5079, of the same Beijing family. Compared with three human M. tb Beijing family strains, the strain 1458 has the fewest unique genes. However, there are most (21) IS6110 insertion sequences in the strain 1458 genome at either intragenic or intergenic sites, resulting in the interruption of 11 genes including three PPE family-encoding genes (PPE16, PPE38, and PPE59). Only the strain 1458 genome has the upstream insertion in esxS and phoP genes. PCR confirmed four upstream insertions and qPCR determined that transcription of esxS, phoP, dnaN, and ctpD genes differed significantly between M. tb strain 1458 and H37Rv or M. bovis. A Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that the genes affected by non-synonymous SNPs are enriched in RNA polymerase. Moreover, 127 of the 133 unique SNPs in strain 1458 are either different to those in the M. bovis genome. In conclusion, some critical genes responsible for bacterial virulence and immunogenicity were interrupted in the genome of bovine M. tb strain 1458 by IS insertions and non-synonymous SNPs, which might contribute to its bovine adaptation, and the modification of its virulence and immunogenicity in cattle.
Highlights
Tuberculosis (TB) is one of the most serious infectious diseases of humans worldwide, in terms of the numbers of cases and deaths
We identified 4,349 open reading frames (ORFs) in the genome, with an average length of 915 bp, which occupy 90.4% of the genome
TB in humans and other species caused by the Mycobacterium tuberculosis complex (MTBC) is considered to be a zoonotic infectious disease, MTBC members have apparent host preferences, as evidenced by the fact that M. tb causes human TB, while M. bovis is responsible for TB in bovines and a wide range of other animals
Summary
Tuberculosis (TB) is one of the most serious infectious diseases of humans worldwide, in terms of the numbers of cases and deaths. According to the Global Tuberculosis Report 2016 from the World Health Organization, there were 10.4 million new TB cases and 1.4 million TB deaths in 2015 (World Health Organization, 2016). Human TB is usually caused by Mycobacterium tuberculosis, while bovine TB is caused by Mycobacterium bovis. Because direct evidence of bovines infected by M. tb is limited, M. tb is usually thought to be avirulent to cattle, or only cause transient infections in cattle (Whelan et al, 2010). In addition to cattle, M. bovis has the capacity to cause TB in a broad of mammal hosts, such as humans, deer, badgers, and possums (Perez-Lago et al, 2014). It was estimated that ∼10% of TB cases are caused by M. bovis which might vary with the regions, it is thought that M. bovis cannot be transmitted among humans (Berg and Smith, 2014)
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