Differential distribution of novel restriction-modification systems in clonal lineages of Neisseria meningitidis

Using representational difference analysis, we isolated novel meningococcal restriction-modification (R-M) systems. NmeBI, which is a homologue of the R-M system HgaI of Pasteurella volantium, was present in meningococci of t he ET-5 complex and of lineage III. NmeAI was found in serogroup A, ET-37 c omplex and cluster A4 meningococci. NmeDI was harbored by meningococci of t he ET-37 complex and of cluster A4, but not by serogroup A meningococci. Tw o of the R-M systems, NmeBI and NmeDI, were located at homologous positions between the phenylalanyl-tRNA synthetase genes pheS and pheT, which appear ed to be a preferential target for the insertion of foreign DNA in meningoc occi. The distribution of the three R-M systems was tested with 103 meningo coccal strains comprising 49 sequence types. The vast majority of the strai ns had either NmeBI, NmeAI, or both NmeAI and NmeDI. Using cocultivation ex periments, we could demonstrate that NmeBI, which was present in ET-5 compl ex meningococci, was responsible for a partial restriction of DNA transfer from meningococci of the ET-37 complex to meningococci of the ET-5 complex.