Involvement of genes of genome maintenance in the regulation of phase variation frequencies in Neisseria meningitidis

Abstract

In Neisseria meningitidis, the reversible expression of surface antigens, i.e. phase variation, results from changes within repeated simple sequence motifs located in coding or promoter regions of the genes involved in their biosynthesis. The mutation rates of these simple sequences, which have a major influence on the generation of phenotypic diversity, can affect the fitness of the population. The aim of the present study was to investigate the involvement of genetic factors involved (mutS and dam) and not yet analysed (drg and dinB) in the regulation of phase variation frequencies of genes associated with a variety of repeat tracts. The frequency of frameshifts occurring in the polycytidine (polyC) tracts associated with siaD, spr and lgtG and in the tetranucleotide (TAAA) repeat tract associated with nadA was determined by colony immunoblotting or using the lacZ gene as a reporter. Inactivation of mutS increased the frequency of phase variation of genes presenting homopolymeric tracts of diverse length. Overexpression of dinB enhanced the instability of the homopolymeric tract associated with siaD. Investigation of the dam locus in a population of genetically distinct N. meningitidis strains revealed that 27 % of strains associated with invasive disease contained the dam gene. In all strains where a Dam function was absent, the drg gene had been inserted into the dam locus. Disruption of dam and drg in strains representative of each genotype, i.e. dam + /drg and dam/drg + , did not modify phase variation frequencies. In contrast to the effects of certain genes on homopolymeric tracts, none of the genetic factors investigated affected the stability of tetranucleotide repeat tracts.

Mismatch Correction Modulates Mutation Frequency and Pilus Phase and Antigenic Variation in Neisseria gonorrhoeae

“…2). Similar low increases in the frequency of spontaneous mutation have previously been reported for mutS and mutL mutants in N. meningitidis (7,26,38). Therefore, mutS and mutL are functional MMC genes in Gc and have modest effects on the correction of point mutations in this organism.…”

A Conserved Tetranucleotide Repeat Is Necessary for Wild-Type Expression of the Moraxella catarrhalis UspA2 Protein

“…The MC58 strain of N. meningitidis has been reported to possess at least 65 genes which have or are associated with nucleotide repeats (35). Other bacterial genes that affect phase variation frequencies of homopolymeric nucleotide repeats in N. meningitidis (34) and those of heteropolymeric nucleotide repeats in H. influenzae (8) have been identified.…”

“…In an exception to the usual "up-or-down" effect on transcription, changes in the number of GAA trinucleotide repeats upstream from the transcriptional start site for the Mycoplasma gallisepticum pMGA genes can ablate expression of these genes (31). Nucleotide repeats and their potential role in contingency loci have probably been most thoroughly examined in Neisseria meningitidis and Haemophilus influenzae (7,(33)(34)(35)49). The availability of completely sequenced genomes for both pathogens (18,46,52) has greatly facilitated these types of analyses.…”

Investigation on the Effect of Immune Selection on Resistance to Bactericidal Antibodies to Group B Meningococci In Vitro

“…This process was repeated for up to five rounds of selection. We chose to use five rounds of 10-fold reduction in colony counts (overall, a 10,000-fold selection) based on studies of phase variation in MenB in which individual genes underwent phase variation with frequencies of 1 in 10 4 to 1 in 10 5 (9). A pool of surviving colonies was used in each round instead of single colonies being picked posttreatment to optimize the chance of passaging a selection variant.…”