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Infection and Immunity, August 2006, p. 4892-4899, Vol. 74, No. 8
0019-9567/06/$08.00+0     doi:10.1128/IAI.02087-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Plasmid Diversity in Neisseriae

Mark W. J. van Passel, Arie van der Ende, and Aldert Bart^*

Center of Infection and Immunity Amsterdam (CINIMA), Department of Medical Microbiology, Academic Medical Center, Amsterdam, The Netherlands

Received 28 December 2005/ Returned for modification 9 March 2006/ Accepted 11 May 2006

Horizontal gene transfer constitutes an important force in prokaryotic genome evolution, and it is well-known that plasmids are vehicles for DNA transfer. Chromosomal DNA is frequently exchanged between pathogenic and commensal neisseriae, but relatively little is known about plasmid diversity and prevalence among these nasopharyngeal inhabitants. We investigated the plasmid contents of 18 Neisseria lactamica isolates and 20 nasopharyngeal Neisseria meningitidis isolates. Of 18 N. lactamica strains, 9 harbored one or more plasmids, whereas only one N. meningitidis isolate contained a plasmid. Twelve plasmids were completely sequenced, while five plasmid sequences from the public databases were also included in the analyses. On the basis of nucleic acid sequences, mobilization, and replicase protein alignments, we distinguish six different plasmid groups (I to VI). Three plasmids from N. lactamica appeared to be highly similar on the nucleotide level to the meningococcal plasmids pJS-A (>99%) and pJS-B (>75%). The genetic organizations of two plasmids show a striking resemblance with that of the recently identified meningococcal disease-associated (MDA) phage, while four putative proteins encoded by these plasmids show 25% to 39% protein identity to those encoded by the MDA phage. The putative promoter of the gene encoding the replicase on these plasmids contains a polycytidine tract, suggesting that replication is subjected to phase variation. In conclusion, extensive plasmid diversity is encountered among commensal neisseriae. Members of three plasmid groups are found in both pathogenic and commensal neisseriae, indicating plasmid exchange between these species. Resemblance between plasmids and MDA phage may be indicative of dissemination of phage-related sequences among pathogenic and commensal neisseriae.

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* Corresponding author. Mailing address: Department of Medical Microbiology, Academic Medical Center, P.O. Box 22660, 1100 DD Amsterdam, The Netherlands. Phone: 31 20 5664863. Fax: 31 20 6979271. E-mail: a.bart{at}amc.uva.nl.

Editor: V. J. DiRita

Supplemental material for this article may be found at http://iai.asm.org/.

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Infection and Immunity, August 2006, p. 4892-4899, Vol. 74, No. 8
0019-9567/06/$08.00+0     doi:10.1128/IAI.02087-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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