Pathogenomic evidence suggests that Mycobacterium tuberculosis (MTB) evolved from an environmental ancestor similar to Mycobacterium canettii, a rare human pathogen. Although the adaptations responsible for this transition are poorly characterized, the ability to persist in humans seems to be important. We set out to identify the adaptations contributing to the evolution of persistence in MTB. We performed an experimental evolution of eight M. canettii populations in mice; four populations were derived from the isolate STB-K (phylogenomically furthest from MTB) and four from STB-D (closest to MTB), which were monitored for 15 and 6 cycles, respectively. We selected M. canettii mutants with enhanced persistence in vivo compared with the parental strains, which were phenotypically closer to MTB. Genome sequencing of 140 mutants and complementation analysis revealed that mutations in two loci were responsible for enhanced persistence. Most of the tested mutants were more resistant than their parental strains to nitric oxide, an important effector of immunity. Modern MTB were similarly more resistant to nitric oxide than M. canettii. Our findings demonstrate phenotypic convergence during experimental evolution of M. canettii, which mirrors natural evolution of MTB. Furthermore, they indicate that the ability to withstand host-induced stresses was key for the emergence of persistent MTB.

致病基因组学证据表明，结核分枝杆菌(MTB) 是从与罕见的人类病原体卡内蒂分枝杆菌相似的环境祖先进化而来的。尽管导致这种转变的适应特征很差，但在人类中持续存在的能力似乎很重要。我们着手确定有助于 MTB 持久性演变的适应。我们对小鼠中的 8 个M. canettii种群进行了实验性进化。四个种群来自分离株 STB-K（系统发育学上距离 MTB 最远）和四个来自 STB-D（最接近 MTB），分别监测 15 和 6 个周期。我们选择了M. canettii与在表型上更接近 MTB 的亲本菌株相比，体内持久性增强的突变体。140 个突变体的基因组测序和互补分析表明，两个基因座中的突变是增强持久性的原因。大多数测试的突变体比它们的亲本菌株对一氧化氮的抵抗力更强，一氧化氮是一种重要的免疫效应物。现代 MTB 同样比M. canettii更能抵抗一氧化氮。我们的研究结果证明了M. canettii实验进化过程中的表型趋同，这反映了 MTB 的自然进化。此外，他们指出，承受宿主诱导压力的能力是持久性 MTB 出现的关键。