Restriction-modification (R-M) systems are often regarded as bacterial immune systems, protecting cells from infection by foreign mobile DNA. However, previous results from our group1 found more R-M systems in genomes carrying more mobile DNA in apparent contradiction with these claims. Now, in a study published in PNAS2, we have used comparative genomics in 79 bacterial species to clarify the role of R-M systems as barriers or facilitators of genetic exchanges. This study shows that more genetic exchanges take place within species with more R-M systems, but within species, transfer is more frequent between strains with compatible R-M systems. Because the repertoire and/or specificity of R-M systems in bacterial lineages vary quickly, the preferential fluxes of genetic transfer within species are constantly changing, producing time-dependent networks of gene transfer.
1 Oliveira PH, Touchon M, and Rocha EPC (2014). Nucleic Acids Res. 42, 10618-31.
2 Oliveira PH, Touchon M, and Rocha EPC (2016). Proc. Natl. Acad. Sci. 113, 5658-63.