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 hipBAXn2 TA system. This TA system was identified in the genome of X. nematophila ATCC 19061, which consists of the hipAXn2 toxin gene encoding 278 amino acid residues and hipBXn2 encoding antitoxin of 135 amino acid residues. We showed that overexpression of HipAXn2 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 hipBAXn2 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 HipAXn2 toxin and HipBXn2 antitoxin to their promoter. This study provides evidence for the presence of a functional and well-regulated hipBAXn2 TA system in X. nematophila.
Keywords: Xenorhabdus nematophila. Toxin-antitoxin. hipBA. Promoter. overexpression. Escherichia coli.
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