HigB1 Toxin in Mycobacterium tuberculosis Is Upregulated During Stress and Required to Establish Infection in Guinea Pigs.

Arun Sharma,Neeraj Kumar Chauhan,Tannu Priya Gosain,Nidhi Gupta,Nikhil Bhalla,Amita Gupta,Balaji Venkataraman,Ramandeep Singh,Kalpana Sagar

doi:10.3389/fmicb.2021.748890

Abstract

The extraordinary expansion of Toxin Antitoxin (TA) modules in the genome of Mycobacterium tuberculosis has received significant attention over the last few decades. The cumulative evidence suggests that TA systems are activated in response to stress conditions and are essential for M. tuberculosis pathogenesis. In M. tuberculosis, Rv1955-Rv1956-Rv1957 constitutes the only tripartite TAC (Toxin Antitoxin Chaperone) module. In this locus, Rv1955 (HigB1) encodes for the toxin and Rv1956 (HigA1) encodes for antitoxin. Rv1957 encodes for a SecB-like chaperone that regulates HigBA1 toxin antitoxin system by preventing HigA1 degradation. Here, we have investigated the physiological role of HigB1 toxin in stress adaptation and pathogenesis of Mycobacterium tuberculosis. qPCR studies revealed that higBA1 is upregulated in nutrient limiting conditions and upon exposure to levofloxacin. We also show that the promoter activity of higBA1 locus in M. tuberculosis is (p)ppGpp dependent. We observed that HigB1 locus is non-essential for M. tuberculosis growth under different stress conditions in vitro. However, guinea pigs infected with higB1 deletion strain exhibited significantly reduced bacterial loads and pathological damage in comparison to the animals infected with the parental strain. Transcriptome analysis suggested that deletion of higB1 reduced the expression of genes involved in virulence, detoxification and adaptation. The present study describes the role of higB1 toxin in M. tuberculosis physiology and highlights the importance of higBA1 locus during infection in host tissues.

Highlights

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis) is a major health concern and infects nearly one-third of the world population
Mycobacterium tuberculosis higBA1 locus is unusual as the toxin (HigB1, Rv1955) and antitoxin (HigA1, Rv1956) are co-transcribed along with the upstream gene, Rv1954A and the downstream gene Rv1957 (Cole et al, 1998; Figure 1A)
It has been shown that HigB1 overexpression results in growth arrest in M. tuberculosis and E. coli (Gupta, 2009; Schuessler et al, 2013)

Summary

Introduction

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M. tuberculosis) is a major health concern and infects nearly one-third of the world population. There is a significant increase in the number of patients infected with the M. tuberculosis. Characterization of HigB1 Toxin of M. tuberculosis strain resistant to front-line TB drugs such as isoniazid and rifampicin. Studies have shown that the proportion of TB patients infected with multi-drug resistant strains lies in the range of 4.6– 25% (Lange et al, 2019). Control of the spread of drug-resistant TB and eradication of TB is hampered by the limited efficacy of therapeutic approaches against drug resistant M. tuberculosis strains and our poor understanding of the strategies used by the pathogen for survival inside the human host. M. tuberculosis has emerged as a highly successful intracellular pathogen due to its ability to sense extracellular stimuli and reprogram metabolic pathways that enables it to survive in host tissues under varied stress conditions

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