Sequencing-relative to hybridization-based transcriptomics approaches better define Mycobacterium tuberculosis stress-response regulons

WhiB4 Is Required for the Reactivation of Persistent Infection of Mycobacterium marinum in Zebrafish

Granulomas are the pathological hallmark of tuberculosis (TB). In individuals with latent TB infection, Mycobacterium tuberculosis cells reside within granulomas in a nonreplicating dormant state, and a portion of them will develop active TB. Little is known on the bacterial mechanisms/factors involved in this process. In this study, we found that WhiB4, an oxygen sensor and a transcription factor, plays a critical role in disease progression and reactivation of Mycobacterium marinum (M. marinum) infection in zebrafish. We show that the whiB4::Tn mutant of M. marinum caused persistent infection in adult zebrafish, which is characterized by the lower but stable bacterial loads, constant number of nonnecrotized granulomas in fewer organs, and reduced inflammation compared to those of zebrafish infected with the wild-type bacteria or the complemented strain. The mutant bacteria in zebrafish were also less responsive to antibiotic treatments. Moreover, the whiB4::Tn mutant was defective in resuscitation from hypoxia-induced dormancy and the DosR regulon was dysregulated in the mutant. Taken together, our results suggest that WhiB4 is a major driver of reactivation from persistent infection.

IMPORTANCE About one-quarter of the world’s population has latent TB infection, and 5 to 10% of those individuals will fall ill with TB. Our finding suggests that WhiB4 is an attractive target for the development of novel therapeutics, which may help to prevent the reactivation of latent infection, thereby reducing the incidences of active TB.

The Regulation of ManLAM-Related Gene Expression in Mycobacterium tuberculosis with Different Drug Resistance Profiles Following Isoniazid Treatment

Introduction

Tuberculosis (TB) caused by Mycobacterium tuberculosis (MTB) remains a global health concern because of the development of drug resistance. The adaptability of MTB in response to a variety of environmental stresses is a crucial strategy that supports their survival and evades host defense mechanisms. Stress regulates gene expression, particularly virulence genes, leading to the development of drug tolerance. Mannose-capped lipoarabinomannan (ManLAM) is a critical component of the cell wall, functions as a virulence factor and influences host defense mechanisms.

Purpose

This study focuses on the effect of isoniazid (INH) stress on the regulation of ManLAM-related genes, to improve our understanding of virulence and drug resistance development in MTB.

Materials and Methods

MTB with distinct drug resistance profiles were used for gene expression analysis. Multiplex-real time PCR assay was performed to monitor stress-related genes (hspX, tgs1, and sigE). The expression levels of ManLAM-related genes (pimB, mptA, mptC, dprE1, dprE2, and embC) were quantified by qRT-PCR. Sequence analysis of drug resistance-associated genes (inhA, katG, and rpoB) and ManLAM-related genes were performed to establish a correlation between genetic variation and gene expression.

Results

INH treatment activates the stress response mechanism in MTB, resulting in a distinct gene expression pattern between drug resistance and drug-sensitive TB. In response to INH, hspX was up-regulated in RIF-R and MDR. tgs1 was strongly up-regulated in MDR, whereas sigE was dramatically up-regulated in the drug-sensitive TB. Interestingly, ManLAM-related genes were most up-regulated in drug resistance, notably MDR (pimB, mptA, dprE1, and embC), implying a role for drug resistance and adaptability of MTB via ManLAM modulation.

Conclusion

This study establishes a relationship between the antibiotic stress response mechanism and the expression of ManLAM-related genes in MTB samples with diverse drug resistance profiles. The novel gene expression pattern in this work is valuable knowledge that can be applied for TB monitoring and treatment in the future.

Transcriptome Changes of Mycobacterium marinum in the Process of Resuscitation From Hypoxia-Induced Dormancy

Nearly one-third of the world's population is latently infected with Mycobacterium tuberculosis (M. tb), which represents a huge disease reservoir for reactivation and a major obstacle for effective control of tuberculosis. During latent infection, M. tb is thought to enter nonreplicative dormant states by virtue of its response to hypoxia and nutrient-deprived conditions. Knowledge of the genetic programs used to facilitate entry into and exit from the nonreplicative dormant states remains incomplete. In this study, we examined the transcriptional changes of Mycobacterium marinum (M. marinum), a pathogenic mycobacterial species closely related to M. tb, at different stages of resuscitation from hypoxia-induced dormancy. RNA-seq analyses were performed on M. marinum cultures recovered at multiple time points after resuscitation. Differentially expressed genes (DEGs) at each time period were identified and analyzed. Co-expression networks of transcription factors and DEGs in each period were constructed. In addition, we performed a weighted gene co-expression network analysis (WGCNA) on all genes and obtained 12 distinct gene modules. Collectively, these data provided valuable insight into the transcriptome changes of M. marinum upon resuscitation as well as gene module function of the bacteria during active metabolism and growth.

Opening Pandora's Box: Mechanisms of Mycobacterium tuberculosis Resuscitation

Mycobacterium tuberculosis (Mtb) characteristically causes an asymptomatic infection. While this latent tuberculosis infection (LTBI) is not contagious, reactivation to active tuberculosis disease (TB) causes the patient to become infectious. A vaccine has existed for TB for a century, while drug treatments have been available for over 70 years; despite this, TB remains a major global health crisis. Understanding the factors which allow the bacillus to control responses to host stress and mechanisms leading to latency are critical for persistence. Similarly, molecular switches which respond to reactivation are important. Recently, research in the field has sought to focus on reactivation, employing system-wide approaches and animal models. Here, we describe the current work that has been done to elucidate the mechanisms of reactivation and stop reactivation in its tracks.