Wenche Blix Gundersen

Polypeptides encoded by cryptic plasmids from Neisseria gonorrhoeae

Almost all clinical isolates of Neisseria gonorrhoeae harbor a small, phenotypically cryptic plasmid of approximately 4.1 kb. In this study several polypeptides encoded by two variants of such plasmids, one (pSB01C) having a deletion of approximately 50 bp as compared to the other (p31788C), have been identified, and the position of the genes for two of the proteins determined. The cryptic plasmids were cloned into the HindIII site of the vectors pBR322 and pACYC184. The resulting recombinant plasmids were transformed into the Escherichia coli minicell producing strain DS410 (minA, minB) and the plasmid-encoded proteins analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The pSB01C derivatives express two distinct proteins of 22 and 16 kDa and p31788C two other proteins of 24 and 18.5 kDa. Additionally, both plasmids express common proteins of 32.5, 9, and 7.5 kDa. The genes coding for the 24- and the 7.5 kDa proteins have been mapped by restriction enzyme analysis of Tn5 insertions suppressing the expression. The additional 50 bp in p31788C are localized to the coding region of the 24-kDa protein, and the 22-kDa protein of pSB01C is possibly a shortened form of the former due to the lacking 50 bp.

Homology between cryptic plasmid from Neisseria gonorrhoeae and genomic DNA from Neisseria meningitidis

The human pathogenic Neisseria species N. gonorrhoeae and N. meningitidis are closely related. In contrast to N. meningitidis, however, almost all clinical isolates of N. gonorrhoeae harbour a pheno‐typically cryptic plasmid. In some gonococcal strains regions of the cryptic plasmid have been found in the gonococcal genome and it has been suggested that large segments of the cryptic plasmid can be integrated into the gonococcal chromosome of both plasmid‐bearing and plasmid‐free strains. Here we report homology between parts of the cryptic gonococcal plasmid and genomic DNA from four different N. meningitidis strains from systemic disease isolates in which no plasmids have been found with the applied methods. Serogroup B strains, causing many of the cases of meningococcal disease in Norway, hybridized strongly to the cryptic plasmid probe, in contrast to serogroup A and C strains. Clones hybridizing to the cryptic plasmid were isolated from a meningococcal genomic Λ EMBL3 DNA library and characterized by restriction mapping. When using one such clone as a probe the parts of the cryptic plasmid showing homology to the genomic meningococcal DNA were confined to two small separate regions of 420 and 88 bp.