Identification of Neisseria meningitidis genetic loci involved in the modulation of phase variation frequencies

Abstract

It has been proposed that increased phase variation frequencies in Neisseria meningitidis augment transmissibility and invasiveness. A Himar1 mariner transposon mutant library was constructed in serogroup A N. meningitidis and screened for clones with increased phase variation frequencies. Insertions increasing the frequency of slippage events within mononucleotide repeat tracts were identified in three known phase variation-modulating genes (mutS, mutL, and uvrD), as well as six additional loci (pilP, fbpA, fbpB, NMA1233, and two intergenic regions). The implications of these insertion mutations are discussed.

FIG. 1.

Representative phenotypes for various hmbR phase variation frequencies. The wild-type strain grows around Hb-saturated filter disks on iron-restricted media in a few distinct colonies (IR4162). Mutants exhibiting increased phase variation phenotypes have increased numbers of colonies representing more hmbR phase “on” cells (739C and 77D).

FIG. 2.

Increased phase variation frequencies resulting from Himar1 mariner transposon insertions. Each bar represents the median of at least six independent measurements, with error bars depicting plus or minus quartiles.

FIG. 3.

Southern blot hybridization analysis of Himar1 mariner insertion mutants using a mariner-specific DNA probe. Genomic DNA was digested with ClaI. Lane kb, 1 kb DNA ladder (Promega); lane WT, IR4162.

FIG. 4.

Increased phase variation frequencies of Fbp mutants. Each bar represents the median of at least six independent measurements, with error bars depicting plus or minus quartiles.