Functional and Transcriptional Analysis of Chromosomal Encoded hipBAXn2 Type II Toxin-Antitoxin (TA) Module From Xenorhabdus Nematophila
Abstract Xenorhabdus nematophila is an entomopathogenic bacterium that synthesizes numerous toxins and kills its larval host. The genome of this bacterium also encodes a total of 39 putative toxin-antitoxin (TA) systems. These systems are also associated with maintaining the bacterial genomic stability and survival of bacteria under adverse environmental conditions. Three hipBA TA homologs were identified on the chromosome of X. nematophila, among them first hipBAXn TA has been studied, second hipBAXn2 TA is still unexplored while third hipBAXn3 TA has been reported as a pseudo-type TA system. Thus, for the first time, here, we are exploring the functionality of the type II hipBAXn2 TA system. This TA system was identified in the genome of X. nematophila ATCC 19061 (NCBI Refseq NC_014228) at position 3774379–3775635 bp, which consists of hipAXn2 toxin gene encoding 270 amino acid residues protein and hipBXn2 encoding antitoxin of 135 amino acid residues protein. It was observed that the overexpression of HipAXn2 toxin inhibits the growth of Escherichia coli cells in a bacteriostatic manner and amino-acids G8, H164, N167, and S169 were key residues for its toxicity. Promoter activity and expression profiling of messenger RNA from the hipBAXn2 TA system was also studied and showed that it was activated 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 the first evidence for the presence of a functional and active hipBAXn2 TA system in X. nematophila.