Adding it up: mycobacteria growth heterogeneity and antibiotic susceptibility

Mycobacterium tuberculosis infects billions of people worldwide and kills more than 1.5 million per year. TB remains extremely difficult to treat with antibiotics, requiring months to years of therapy for cure. The variable course of disease and treatment response suggests that functionally heterogeneous populations of mycobacteria respond differently to stress. Using a quantitative single-cell approach, we show that mycobacteria deterministically generate diversity in their growth characteristics through asymmetric growth and maintain a controlled but asymmetric chromosomal organization pattern. Coupled with a unique mechanism of cell size regulation utilizing parallel adders from initiation, this asymmetry creates subpopulations of cells with distinct growth rates and cell sizes that are differentially susceptible to clinically relevant classes of antibiotics. We find that combinations of inherent and temporal properties of individual cells describe subpopulations susceptible to different antibiotics. Thus, the polar growth pattern intrinsic to mycobacteria deterministically creates a diverse population structure that may underlie phenotypes previously thought to be controlled by external stressors. Mathematical models based on measurements from new reporters of cell state enable us to better understand how mycobacteria manage growth variation and generate subpopulations with distinct behaviors arising from asymmetric growth and division.