Development of phenotypic heterogeneity in different environmental niches in <i>Mycobacterium tuberculosis</i>

Mycobacterium tuberculosis (Mtb) infects billions of people worldwide and kills more than 1.5 million per year. TB remains a major cause of death worldwide. TB is difficult to treat because the bacteria occupy lesions that create pockets of persisters. The variable course of disease and treatment response suggests that functionally heterogeneous populations of mycobacteria respond differently to stress. We describe how mycobacteria deterministically generate diversity in their growth characteristics through asymmetric growth and division. Coupled with a unique mechanism of cell size regulation utilizing parallel adders from initiation, this asymmetry creates subpopulations of cells with distinct cell sizes that are differentially susceptible to antibiotics. This innate heterogeneity gives rise to subpopulations of cells that are differentially susceptible to clinically relevant classes of antibiotics. We find that Mtb alter their cell size distributions under different environmental stressors that are encountered in the host in a strain-specific manner. We combine quantitative live-cell imaging, fixed-cell imaging, and mathematical modeling to understand how Mtb cell growth and replication processes are mediated in various environmental conditions encountered in host tissues and how these characteristics determine antibiotic susceptibility.