Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2012
Publication Date: 4/20/2012
Citation: Lee, S., Ward, T.J., Siletzky, R.M., Kathariou, S. 2012. Two novel type II restriction-modification (RM) systems occupying genomically equivalent locations on the chromosomes of Listeria monocytogenes strains. Applied and Environmental Microbiology. 78(8):2623-2630. Interpretive Summary: Listeria monocytogenes is a food-borne bacterium that places a serious burden on human health and the agricultural economy. However, not all L. monocytogenes strains are equally likely to persist in food environments. In this study, we characterized two novel restriction modification (RM) systems that Listeria utilize to defend themselves against predation by phage viruses. Strains harboring these RM systems may have an advantage over other bacterial strains in food and other environments in which certain phage viruses exist. The identification and characterization of the two novel RM systems described in this study provides information regarding the genetic basis for differences in environmental prevalence among Listeria monocytogenes strains. In addition, the data on RM prevalence and distribution will be of use in selecting appropriate phages for use as biocontrol agents, and also contributes to understanding of the efficiency. These data will be of direct interest to epidemiologists, public health and food inspection agencies, and scientists involved in food safety research.
Technical Abstract: Listeria monocytogenes is responsible for the potentially life-threatening foodborne disease listeriosis. One epidemic-associated clonal group of L. monocytogenes, epidemic clone I (ECI), harbors a Sau3AI-like restriction-modification (RM) system also present in the same genomic region in certain strains of other lineages. In this study, we identified and characterized two other, novel Type II RM systems, LmoJ2 and LmoJ3, at this same locus. LmoJ2 and LmoJ appeared to recognize GCWGC (W=A or T) and GCNGC, respectively. Both RM systems consisted of genes with GC content below the genome average and were in the same genomic region in strains of different serotypes and lineages, suggesting site-specific horizontal gene transfer. Genomic DNA from LmoJ2 and LmoJ3 strains grown at various temperatures (4-42ºC) was resistant to digestion with restriction enzymes recognizing GCWGC or GCNGC, indicating that the methyltransferases were expressed under these conditions. Phages propagated in a LmoJ2-harboring strain exhibited moderately increased (up to 7.9 fold) infectivity for this strain at 4 and 8ºC but not at higher temperatures, while phages propagated in a LmoJ3 strain had dramatically increased (up to 105.9 fold) infectivity for this strain at all temperatures. Among the sequenced Listeria phages, lytic phages possessed significantly fewer recognition sites for these RM systems than lysogenic phages, suggesting that in lytic phages sequence content evolved towards reduced susceptibility to such RM systems. The ability of LmoJ2 and LmoJ3 to protect against phages may affect the efficiency of phages as biocontrol agents for L. monocytogenes strains harboring these RM systems.