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

Abstract

The extraordinary expansion of Toxin Antitoxin (TA) modules in the genome of <i>Mycobacterium tuberculosis</i> 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 <i>M. tuberculosis</i> pathogenesis. In <i>M. tuberculosis</i>, 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 <i>Mycobacterium tuberculosis</i>. qPCR studies revealed that <i>higBA</i>1 is upregulated in nutrient limiting conditions and upon exposure to levofloxacin. We also show that the promoter activity of <i>higBA</i>1 locus in <i>M. tuberculosis</i> is (p)ppGpp dependent. We observed that HigB1 locus is non-essential for <i>M. tuberculosis</i> growth under different stress conditions <i>in vitro</i>. However, guinea pigs infected with <i>higB</i>1 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 <i>higB</i>1 reduced the expression of genes involved in virulence, detoxification and adaptation. The present study describes the role of <i>higB</i>1 toxin in <i>M. tuberculosis</i> physiology and highlights the importance of <i>higBA</i>1 locus during infection in host tissues.