Abstract
Mycobacterial granulomas lie at the center of tuberculosis (TB) pathogenesis and represent a unique niche where infecting bacteria survive under nutrient-restricted conditions and in the face of a host immune response. The granuloma's necrotic core, where bacteria reside extracellularly in humans, is difficult to assess in many experimentally tractable models. Here, using necrotic mycobacterial granulomas in adult zebrafish, we develop dual RNA sequencing (RNA-seq) across different host genotypes to identify the transcriptional alterations that enable bacteria to survive within this key microenvironment. Using pharmacological and genetic interventions, we find that neutrophils within mature, necrotic granulomas promote bacterial growth, in part through up-regulation of the bacterial devR regulon. We identify conserved suites of bacterial transcriptional programs induced only in the context of this unique necrotic extracellular niche, including bacterial modules related to K(+) transport and rpf genes. Analysis of Mycobacterium tuberculosis strains across diverse lineages and human populations suggests that granuloma-specific transcriptional modules are targets for bacterial genetic adaptation in the context of human infection.