Prabhat Ranjan Singh

Mycobacterium tuberculosis (Mtb) must survive multiple changes in environment for aerosol transmission. Our genome-wide screen for rehydration of modeled aerosols in surrogate pulmonary alveolar lining fluid identified a survival-sustaining role for 22 genes not required for survival during earlier stages of transmission, 20 of which are non-essential in routine culture. Thirteen genes were also needed for Mtb to survive in alveolar macrophages after passing through the earlier stages of transmission. Nine 9 of the 13 were needed for full infectivity of aerosols in mice. Seven of the genes sustaining the intra-alveolar survival of aerosolized Mtb are likely to regulate Mtb’s uptake, catabolism or synthesis of lipids as regulated by cAMP. Our results reveal a dynamic form of conditional essentiality that only emerges after bacteria experience a sequence of other pathophysiologically relevant conditions. These findings enlarge Mtb’s candidate transmission survival genome with stage-specific genes encoding potential targets for blocking tuberculosis transmission.

M. tuberculosis retains the unique ability to establish an asymptomatic latent infection. To understand the mechanisms involved in hypoxic stress which play a critical role in persistence, we show that the virulence regulator PhoP is linked to hypoxia, the dormancy signal. In keeping with this, phoP was shown to play a major role in M. tuberculosis growth under hypoxia even in the presence of surplus nitrogen, the alternate electron acceptor. Our results showing regulation of hypoxia-responsive genes provide new biological insights into role of the virulence regulator in metabolic switching by sensing hypoxia and integrating nitrogen metabolism with hypoxia by the assistance of the hypoxia regulator DosR.