JB Accepts, published online ahead of print on 23 October 2009

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J. Bacteriol. doi:10.1128/JB.01228-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Mismatch correction modulates mutation frequency and pilus phase and antigenic variation in Neisseria gonorrhoeae

Alison K. Criss, Kevin M. Bonney, Rhoda A. Chang, Paul M. Duffin, Brian E. LeCuyer, and H. Steven Seifert^*

Department of Microbiology-Immunology, Northwestern Feinberg School of Medicine, Chicago, IL 60611

^* To whom correspondence should be addressed. Email: h-seifert{at}northwestern.edu.

The mismatch correction (MMC) system repairs DNA mismatches and single nucleotide insertions or deletions post-replication. To test the functions of MMC in the obligate human pathogen Neisseria gonorrhoeae, homologues of the core MMC genes mutS and mutL were inactivated in strain FA1090. No mutH homologue was found in the FA1090 genome, suggesting that gonococcal MMC is not methyl-directed. MMC mutants were compared to a mutant in uvrD, the helicase that functions with MMC in E. coli. Inactivation of MMC or uvrD increased spontaneous resistance to rifampicin and nalidixic acid, and MMC/uvrD double mutants exhibited higher mutation frequencies than any single mutant. Loss of MMC marginally enhanced the transformation efficiency of DNA carrying a single nucleotide mismatch but not a 1 kb insertion. Unlike the exquisite UV sensitivity of the uvrD mutant, inactivating MMC did not affect survival after UV irradiation. MMC and uvrD mutants exhibited increased PilC-dependent pilus phase variation. mutS-deficient gonococci underwent an increased frequency of pilin antigenic variation, whereas uvrD had no effect. Recombination tracts in the mutS pilin variants were longer than in parental gonococci but utilized the same donor pilS loci. These results show that gonococcal MMC repairs mismatches and small insertion/deletions in DNA and also affects the recombination events underlying pilin antigenic variation. The differential effects of MMC and uvrD in gonococci unexpectedly reveal that MMC can function independently of uvrD in this human-specific pathogen.