Functional and transcriptional analysis of chromosomal encoded hipBA type II toxin-antitoxin (TA) module from Xenorhabdus nematophila.

Xenorhabdus nematophila is an entomopathogenic bacterium that synthesizes numerous toxins and kills its larval insect host. Apart from such toxins, its genome also has a plethora of toxin-antitoxin (TA) systems. The role of TA systems in bacterial physiology is debatable; however, they are associated with maintaining bacterial genomic stability and their survival under adverse environmental conditions. Here, we explored the functionality and transcriptional regulation of the type II hipBA TA system. This TA system was identified in the genome of X. nematophila ATCC 19061, which consists of the hipA toxin gene encoding 278 amino acid residues and hipB encoding antitoxin of 135 amino acid residues. We showed that overexpression of HipA toxin reduced the growth of Escherichia coli cells in a bacteriostatic manner, and amino-acids G8, H164, N167, and S169 were key residues for this growth reduction. Promoter activity and expression profiling of the hipBA TA system was showed that transcription was induced in both E. coli as well as X. nematophila upon exposure to different stress conditions. Further, we have exhibited the binding features of HipA toxin and HipB antitoxin to their promoter. This study provides evidence for the presence of a functional and well-regulated hipBA TA system in X. nematophila.