The study by Deo Prakash Pandey and Kenn Gerdes investigates the prevalence and distribution of toxin–antitoxin (TA) loci in prokaryotic genomes. TA loci are found in multiple copies in the chromosomes of *Escherichia coli* and are known to help cells survive stressful conditions. The researchers searched 126 completely sequenced prokaryotic genomes (16 archaea and 110 bacteria) and identified 671 TA loci belonging to seven known TA gene families. Surprisingly, obligate intracellular organisms lacked TA loci, while free-living slowly growing prokaryotes had a high number of TA loci. In many cases, TA loci were clustered and linked to mobile genetic elements. The most extreme example was *Vibrio cholerae*, which had 13 TA loci all located within the megaintegron on chromosome II. These findings suggest that TA loci are mobile cassettes that frequently move within and between chromosomes and function as stress-response elements beneficial to free-living prokaryotes. The study also discusses the phylogenetic distribution of TA loci and their potential roles in gene stabilization and quality control.The study by Deo Prakash Pandey and Kenn Gerdes investigates the prevalence and distribution of toxin–antitoxin (TA) loci in prokaryotic genomes. TA loci are found in multiple copies in the chromosomes of *Escherichia coli* and are known to help cells survive stressful conditions. The researchers searched 126 completely sequenced prokaryotic genomes (16 archaea and 110 bacteria) and identified 671 TA loci belonging to seven known TA gene families. Surprisingly, obligate intracellular organisms lacked TA loci, while free-living slowly growing prokaryotes had a high number of TA loci. In many cases, TA loci were clustered and linked to mobile genetic elements. The most extreme example was *Vibrio cholerae*, which had 13 TA loci all located within the megaintegron on chromosome II. These findings suggest that TA loci are mobile cassettes that frequently move within and between chromosomes and function as stress-response elements beneficial to free-living prokaryotes. The study also discusses the phylogenetic distribution of TA loci and their potential roles in gene stabilization and quality control.