Genes encoding structurally independent phosphotriesterases (PTEs) are identified in soil bacteria. These pte genes, often identified on mobilizable and self-transmissible plasmids are organized as mobile genetic elements. Their dissemination through lateral gene transfer is evident due to the detection of identical organophosphate degradation genes among soil bacteria with little orno taxonomic relationship. Convergent evolution of PTEs provided selective advantages to the bacterial strain as they convert toxic phosphotriesters (PTs) into a source of phosphate. The residues of organophosphate (OP) compounds that accumulate in a soil are proposed to contribute to the evolution of PTEs through substrate-assisted gain-of-function. This review provides comprehensiveinformation on lateral transfer of pte genes and critically examines proposed hypotheses on their evolution in the light of the short half-life of OPs in the environment. The review also proposes alternate factors that have possibly contributed to the evolution and lateral mobility of PTEs by taking into account their biology and analyses of pte genes in genomic and metagenomic databases.

Genome sequence of Acinetobacter baumannii DS002 revealed the existence of seven contigs with features of indigenousplasmids. Of the seven contigs, three of them have shown size and sequence identity. They appeared to have been generated due to theunique recombination events leading to a large-scale recombination and sequence inversions. The rest of the indigenous plasmids haveshown significant size variations and contained the genetic repertoire required for the detoxification of formaldehyde and biosynthesis ofexopolysaccharides. Genetic modules encoding novel toxin–antitoxin systems were found in most of the plasmids to ensure their survival inthe host. In some instances, the toxin and antitoxin coding sequences were found on two different plasmids promoting the cosegregation ofthese two plasmids into the daughter cells.