Induced ectopic expression of HigB toxin in M ycobacterium tuberculosis results in growth inhibition, reduced abundance of a subset of mRNAs and cleavage of tmRNA

In M ycobacterium tuberculosis , the genes Rv 1954 A – Rv 1957 form an operon that includes Rv 1955 and Rv 1956 which encode the HigB toxin and the HigA antitoxin respectively. We are interested in the role and regulation of this operon, since toxin–antitoxin systems have been suggested to play a part in the formation of persister cells in mycobacteria. To investigate the function of the higBA locus, effects of toxin expression on mycobacterial growth and transcript levels were assessed in M . tuberculosis H 37 Rv wild type and in an operon deletion background. We show that expression of HigB toxin in the absence of HigA antitoxin arrests growth and causes cell death in M . tuberculosis . We demonstrate HigB expression to reduce the abundance of IdeR and Zur regulated mRNAs and to cleave tmRNA in M . tuberculosis , E scherichia coli and M ycobacterium smegmatis . This study provides the first identification of possible target transcripts of HigB in M . tuberculosis .