title: Horizontal gene transfer of chromosomal Type II toxin-antitoxin systems of Escherichia coli.
abstract: Type II toxin-antitoxin systems (TAs) are small autoregulated bicistronic operons that encode a toxin protein with the potential to inhibit metabolic processes and an antitoxin protein to neutralize the toxin. Most of the bacterial genomes encode multiple TAs. However, the diversity and accumulation of TAs on bacterial genomes and its physiological implications are highly debated. Here we provide evidence that Escherichia coli chromosomal TAs (encoding RNase toxins) are 'acquired' DNA likely originated from heterologous DNA and are the smallest known autoregulated operons with the potential for horizontal propagation. Sequence analyses revealed that integration of TAs into the bacterial genome is unique and contributes to variations in the coding and/or regulatory regions of flanking host genome sequences. Plasmids and genomes encoding identical TAs of natural isolates are mutually exclusive. Chromosomal TAs might play significant roles in the evolution and ecology of bacteria by contributing to host genome variation and by moderation of plasmid maintenance.
authors.affiliation: School of Chemical and Biotechnology, SASTRA University, Tamil Nadu 613402, India ramisettybcm@biotech.sastra.edu.
authors.forename: Bhaskar Chandra Mohan
authors.identifier: http://orcid.org/0000-0003-2511-4162
authors.initials: BC
authors.lastname: Ramisetty
authors.affiliation: School of Chemical and Biotechnology, SASTRA University, Tamil Nadu 613402, India.
authors.forename: Ramachandran Sarojini
authors.initials: RS
authors.lastname: Santhosh
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics*; D019295:Computational Biology; D004926:Escherichia coli / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D014644:Genetic Variation
chemical_list: D001427:Bacterial Toxins
keywords: anti-addiction to plasmids; horizontal gene transfer; non-homologous integration; selfish DNA