Metabolic switching ofMycobacterium tuberculosisduring hypoxia is controlled by the virulence regulator PhoP

Abstract

25Mycobacterium tuberculosis (Mtb) retains the unique ability to establish an asymptomatic 26 latent infection. A fundamental question in mycobacterial physiology is to understand the 27 mechanisms involved in hypoxic stress, a critical player in persistence. Here, we show that the 28 virulence regulator PhoP responds to hypoxia, the dormancy signal and effectively integrates 29 hypoxia with nitrogen metabolism. We also provide evidence to demonstrate that both under 30 nitrogen limiting conditions and during hypoxia, phoP locus controls key genes involved in 31 nitrogen metabolism. Consistently, under hypoxia phoP shows growth attenuation even with 32 surplus nitrogen, the alternate electron acceptor, and complementation of the mutant restores 33 bacterial growth. Together, our observations provide new biological insights into the role of 34 PhoP in integrating nitrogen metabolism with hypoxia by the assistance of the hypoxia regulator 35DosR. The results have significant implications on the mechanism of intracellular survival and 36 growth of the tubercle bacilli under a hypoxic environment within the phagosome. 37 38 Importance 39Mtb retains the unique ability to establish an asymptomatic latent infection. To understand the 40 mechanisms involved in hypoxic stress which plays a critical role in persistence, we show that 41 the virulence regulator PhoP responds to hypoxia, the dormancy signal. In keeping with this, 42 phoP was shown to play a major role in Mtb growth under hypoxia even in presence of surplus 43 nitrogen, the alternate electron acceptor. Our results showing regulation of hypoxia-responsive 44 genes provide new biological insights into role of the virulence regulator in metabolic switching 45 by sensing hypoxia and integrating nitrogen metabolism with hypoxia by the assistance of the 46 hypoxia regulator DosR. 47 48 49 A hallmark of tuberculosis is the unique ability of Mtb to establish an asymptomatic 50 latent infection and persist within granulomas in a dormant form, sometimes for a very long 51 time, before reactivation to cause the active disease. As survival and persistence in this 52 environment depends on the sensing of signals and ability to induce a robust adaptive response, 53 one of the major aspects to understand latent TB relates to understanding molecular mechanism 54 of adaptation of the tubercle bacilli in response to environmental stress. 55 56 Despite its requirement of oxygen for growth, during latency Mtb can survive without 57 oxygen for a surprisingly long time. Thus, two in vivo conditions are often linked to latent TB. 58These are hypoxia and exposure to immune effectors such as nitric oxide (NO) (1-3). The ability 59 to produce reactive nitrogen species (RNS) by host-inducible nitric oxide synthase (iNOS) 60 contributes to TB infections by its effect on both the host and the pathogen (4). Therefore, 61 functional iNOS expression could be detected in the lung macrophages of human TB patients (5, 62 6). Consistently, hypoxia and nitric oxide dependent bacterial adaptation...