DNA methylation in Neisseria gonorrhoeae and other Neisseriae

It has been reported in the literature that Neisseria gonorrhoeae DNA is modified by the methyltransferases (MTases) M.NgoI, M.NgoII, and M.NgoIII, as well as three other cytosine MTases and one adenine MTase, even if the corresponding restriction endonucleases are not present. We envisioned the possibility of cloning one of the N. gonorrhoeae MTase-encoding genes for use as a species-specific DNA probe. We therefore undertook a survey of methylation patterns of several clinical isolates of N. gonorrhoeae and N. meningitidis as well as ATCC strains of other Neisseriae. We found, from digestion patterns with isoschizomers, one N. gonorrhoeae strain that lacked M.NgoII and two that lacked M.NgoIII. All N. meningitidis strains (save one) were resistant to digestion with NlaIV thus possessing an MTase like NgoV, and one was resistant to SstII, thus having an NgoIII-like MTase. None were resistant to isoschizomers of NgoI, NgoIII and NgoIV. Some other Neisseriae had an MTase with NlaIV (NgoV) specificity, but none had NgoI, II, III or IV specificity, except for the Branhamella-like N. caviae-ovis group and N. lactamica where these specificities were present in at least one strain of this group. Therefore, among the Neisseriae other than N. caviae only M.NgoI is N. gonorrhoeae-specific.