TY - JOUR T1 - Redox-dependent condensation of mycobacterial genome by WhiB4 JF - bioRxiv DO - 10.1101/133181 SP - 133181 AU - Manbeena Chawla AU - Mansi Mehta AU - Pankti Parikh AU - Saurabh Mishra AU - Prashant Shukla AU - Priyanka Baloni AU - Manika Vij AU - H N Verma AU - Munia Ganguli AU - Nagasuma Chandra AU - Amit Singh Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/05/02/133181.abstract N2 - Conventionally, oxidative stress response in bacteria is mediated through coordination between the regulators of oxidant-remediation systems (e.g. OxyR, SoxR) and nucleoid condensation (e.g. Dps, Fis). However, Mycobacterium tuberculosis (Mtb) lacks these mechanisms. Therefore, how Mtb organizes genome architecture and regulates gene expression to counterbalance oxidative imbalance during infection is not known. Using systems biology and imaging techniques, we report that an intracellular redox-sensor, WhiB4, dynamically regulates genome condensation and multiple oxidative stress response networks in Mtb. Notably, a low degree of oxidative stress induced marginal genome condensation, while heightened oxidative stress triggered mycobacterial death through nucleoid hyper-condensation. Deletion of WhiB4 alleviated, whereas over-expression aggravated the negative impact of DNA condensation on oxidative stress survival of Mtb. Further, our results suggest that WhiB4 mediates both architectural and regulatory roles by controlling auto-expression, homo-interaction, and hetero-interaction with sigma factors, SigE and SigA, in response to changes in intramycobacterial redox potential. Over-expression of WhiB4 in Mtb disrupts redox homeostasis, damages genome integrity, and synergizes with host-generated radicals to exert efficient killing inside macrophages and mice. Expression of SigE counteracted the deleterious influence of WhiB4 over-expression on nucleoid condensation and survival, indicating that WhiB4-SigE constitutes a system that calibrates oxidative stress response in Mtb. We infer that WhiB4 is a novel redox-dependent architectural protein that structurally couples response to oxidative stress with changes in genome organization and transcription in Mtb. This previously unidentified dependence of Mtb on WhiB4 and nucleoid condensation to modulate oxidative stress response expands our understanding of bacterial pathogenicity.Author Summary In pathogenic mycobacteria, understanding of the concerted rearrangements of gene activities during various stages of infection is a fundamental problem. To persist, Mtb needs to adapt in response to an array of successive environmental challenges encountered during infection. Most of the hostile conditions within host, including acidic and oxidative stress, are known to induce changes in DNA topology in other bacterial systems. Variations in nucleoid condensation in response to changing environmental conditions may serve as a signal triggering the virulence program during the infection process. We deciphered a redox-based mechanistic device, WhiB4, coordinating the chromosomal structure with selective expression of the adaptive traits in response to oxidative stress. Using a holistic approach exploring the inherent relationships between the physicochemical properties of the DNA, cytoplasmic redox potential, and regulation of virulence factors network mediating adaptive potential in Mtb, we uncovered a fundamental basis of oxidative stress tolerance and mycobacterial persistence during infection. ER -