title: A novel restriction-modification system is responsible for temperature-dependent phage resistance in Listeria monocytogenes ECII.
abstract: Listeria monocytogenes epidemic clone II (ECII) strains are unusual in being completely resistant to phage when grown at low temperatures (≤30°C). In the current study we constructed and characterized a mariner-based mutant (J46C) of the ECII strain H7550-Cd(S) that lacked temperature-dependent resistance to phage. The transposon was localized in LMOh7858_2753 (open reading frame [ORF] 2753), a member of a 12-ORF genomic island unique to ECII strains. ORF 2753 and ORF 2754 exhibited homologies to restriction endonucleases and methyltransferases associated with type II restriction-modification (RM) systems. In silico-based predictions of the recognition site for this putative RM system were supported by resistance of DNA from ECII strains to digestion by BfuI, a type II restriction enzyme specific for GTATCC (N6/5). Similarly to J46C, a mutant harboring an in-frame deletion of ORF 2753 was susceptible to phage regardless of temperature of growth (25°C or 37°C). Genetic complementation restored phage resistance in 25°C-grown cells of ORF 2753 mutants. Reverse transcription (RT) and quantitative real-time PCR data suggested enhanced transcription of ORF 2753 at low temperatures (≤25°C) compared to 37°C. In contrast, available transcriptional data suggested that the putative methyltransferase (ORF 2754) was constitutively expressed at all tested temperatures (4 to 37°C). Thus, temperature-dependent resistance of L. monocytogenes ECII to phage is mediated by temperature-dependent expression of the restriction endonuclease associated with a novel RM system (LmoH7) unique to this epidemic clone.
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Kim
authors.forename: Vikrant
authors.initials: V
authors.lastname: Dutta
authors.forename: Driss
authors.initials: D
authors.lastname: Elhanafi
authors.forename: Sangmi
authors.initials: S
authors.lastname: Lee
authors.forename: Jason A
authors.initials: JA
authors.lastname: Osborne
authors.forename: Sophia
authors.initials: S
authors.lastname: Kathariou
mesh_terms: D001435:Bacteriophages / Q000235:genetics / Q000254:growth & development*; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics / Q000378:metabolism*; D004251:DNA Transposable Elements; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D005816:Genetic Complementation Test; D008089:Listeria monocytogenes / Q000201:enzymology* / Q000821:virology*; D016254:Mutagenesis, Insertional; D009154:Mutation; D017384:Sequence Deletion; D013696:Temperature; D014158:Transcription, Genetic
chemical_list: D015280:DNA Restriction-Modification Enzymes; D004251:DNA Transposable Elements; D004279:DNA, Viral