The Mycobacterium tuberculosis Rv2745c Plays an Important Role in Responding to Redox Stress Amanda McGillivray 1,2 , Nadia Abrahams Golden 1 , Uma Shankar Gautam 1 , Smriti Mehra 3 , Deepak Kaushal 1,2 * 1 Divisions of Bacteriology and Parasitology, Tulane National Primate Research Center, Covington, Louisiana, United States of America, 2 Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, Louisiana, United States of America, 3 Division of Microbiology, Tulane National Primate Research Center, Covington, Louisiana, United States of America Abstract Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is the leading cause of death from an infectious disease worldwide. Over the course of its life cycle in vivo, Mtb is exposed to a plethora of environmental stress conditions. Temporal regulation of genes involved in sensing and responding to such conditions is therefore crucial for Mtb to establish an infection. The Rv2745c (clgR) gene encodes a Clp protease gene regulator that is induced in response to a variety of stress conditions and potentially plays a role in Mtb pathogenesis. Our isogenic mutant, Mtb:DRv2745c, is significantly more sensitive to in vitro redox stress generated by diamide, relative to wild-type Mtb as well as to a complemented strain. Together with the fact that the expression of Rv2745c is strongly induced in response to redox stress, these results strongly implicate a role for ClgR in the management of intraphagosomal redox stress. Additionally, we observed that redox stress led to the dysregulation of the expression of the s H /s E regulon in the isogenic mutant, Mtb:DRv2745c. Furthermore, induction of clgR in Mtb and Mtb:DRv2745c (comp) did not lead to Clp protease induction, indicating that clgR has additional functions that need to be elucidated. Our data, when taken together with that obtained by other groups, indicates that ClgR plays diverse roles in multiple regulatory networks in response to different stress conditions. In addition to redox stress, the expression of Rv2745c correlates with the expression of genes involved in sulfate assimilation as well as in response to hypoxia and reaeration. Clearly, the Mtb Rv2745c-encoded ClgR performs different functions during stress response and is important for the pathogenicity of Mtb in-vivo, regardless of its induction of the Clp proteolytic pathway. Citation: McGillivray A, Golden NA, Gautam US, Mehra S, Kaushal D (2014) The Mycobacterium tuberculosis Rv2745c Plays an Important Role in Responding to Redox Stress. PLoS ONE 9(4): e93604. doi:10.1371/journal.pone.0093604 Editor: Gobardhan Das, University of KwaZulu-Natal, South Africa Received January 14, 2014; Accepted March 7, 2014; Published April 4, 2014 Copyright: ß 2014 McGillivray et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by the NIH grants AI089323, with additional support from NIH grants HL106790, AI091457, RR026006, RR020159, RR000164/ OD011104 and C06AI058609. Additionally, the authors also acknowledge the support from the Louisiana Board of Regents (LEQSF (2007-12)-ENHPKSFI- PRS), the Tulane Research Enhancement Fund, the Tulane Center for Infectious Diseases, the Tulane National Primate Research Center Office of the Director and a Bridge Award from the Tulane Office of the Vice-President for Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors confirm that Deepak Kaushal, serve as an academic editor for PLOS ONE. This does not alter the authors’ adherence to PLOS ONE editorial policies and criteria. * E-mail: dkaushal@tulane.edu Introduction One third of the population is infected with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB) [1]. TB is the leading cause of death worldwide from an infectious disease and is responsible for approximately 1.4 million deaths annually [1]. Unfortunately, the current vaccine, Bacillus Calmette-Gue ´rine (BCG) vaccine, has a low protective efficacy against adult pulmonary TB [2,3]. Infected individuals require a long treatment regimen, ranging from 6 to 12 months that involve serious side effects leading to noncompliance, and ultimately the development of resistance. Consequently, understanding the interplay between host and pathogen becomes increasingly important in order to develop alternative treatments and more effective vaccines. One critical step in Mtb pathogenesis is the ability of Mtb to reside within the macrophage (MW) phagolysosome, as infected alveolar macrophages (AMW) are responsible for antigen presen- tation to CD4 + T cells during Mtb infection [4,5]. Residence within the phagolysosome leads to exposure of a plethora of environmental stressors, such as reactive nitrogen species (RNS) and reactive oxygen intermediates (ROI), low pH, and hydrolases, that Mtb must be able to sense and respond to in order to establish an infection [6–9]. Thus, the temporal regulation of genes involved in sensing and responding to environmental stressors becomes increasingly important for understanding the ability of Mtb to take residence within the host MW. Mtb encodes over 200 regulators of transcription including 13 different sigma factors and is well equipped to respond to rapid changes in its environment. Upon residence within the host MW, Mtb intracellular proteins are targets of RNS and ROIs [8]. It is likely that these stress conditions lead to changes in protein conformation, such as misfolding and aggregation. Clearance of misfolded and/or aggregated proteins is necessary for maintenance of protein homeostasis, which is also crucial for infection establishment. One Mtb gene that may play a role in this process is Rv2745c (clgR), which encodes a Clp protease gene regulator that is induced under a variety of stress conditions [10–12]. The expression of Rv2745c appears to be under the control of either s E or s H , or PLOS ONE | www.plosone.org 1 April 2014 | Volume 9 | Issue 4 | e93604