Heterologous Production of 1-Tuberculosinyladenosine in Mycobacterium kansasii Models Pathoevolution towards the Transcellular Lifestyle of Mycobacterium tuberculosis

Abstract

<i>Mycobacterium kansasii</i> is an environmental nontuberculous mycobacterium that causes opportunistic tuberculosis-like disease. It is one of the most closely related species to the <i>Mycobacterium tuberculosis</i> complex. Using <i>M. kansasii</i> as a proxy for the <i>M. kansasii</i>-<i>M. tuberculosis</i> common ancestor, we asked whether introducing the <i>M. tuberculosis</i>-specific gene pair <i>Rv3377c-Rv3378c</i> into <i>M. kansasii</i> affects the course of experimental infection. Expression of these genes resulted in the production of an adenosine-linked lipid species, known as 1-tuberculosinyladenosine (1-TbAd), but did not alter growth <i>in vitro</i> under standard conditions. Production of 1-TbAd enhanced growth of <i>M. kansasii</i> under acidic conditions through a bacterial cell-intrinsic mechanism independent of controlling pH in the bulk extracellular and intracellular spaces. Production of 1-TbAd led to greater burden of <i>M. kansasii</i> in the lungs of C57BL/6 mice during the first 24 h after infection, and <i>ex vivo</i> infections of alveolar macrophages recapitulated this phenotype within the same time frame. However, in long-term infections, production of 1-TbAd resulted in impaired bacterial survival in both C57BL/6 mice and <i>Ccr2^-/-</i> mice. We have demonstrated that <i>M. kansasii</i> is a valid surrogate of <i>M. tuberculosis</i> to study virulence factors acquired by the latter organism, yet shown the challenge inherent to studying the complex evolution of mycobacterial pathogenicity with isolated gene complementation.<b>IMPORTANCE</b> This work sheds light on the role of the lipid 1-tuberculosinyladenosine in the evolution of an environmental ancestor to <i>M. tuberculosis</i> On a larger scale, it reinforces the importance of horizontal gene transfer in bacterial evolution and examines novel models and methods to provide a better understanding of the subtle effects of individual <i>M. tuberculosis</i>-specific virulence factors in infection settings that are relevant to the pathogen.