Genome-Wide Mutational Analyses

On the basis of signature-tagged mutagenesis (STM) of a clinical isolate of N. meningitidis serogroup B strain C311+ (ET5), 73 genes were identified that were essential for bacteremia in an infant rat model [72]. In addition to eight genes encoding already known virulence factors, 65 genes were identified that were not previously known to be involved in meningococcal pathogenesis. Amongst others, two regulatory genes (ntrY and hfq) affecting the transcription at many loci were identified, as were two putative surface-associated ATP-binding cassette transporters. Seven mutants had insertions in genes necessary for the integrity of the cell envelope. In addition to five genes encoding enzymes of the shikimate pathway, an additional six genes involved in amino acid biosynthesis were identified. Although the positions of attenuating mutations were widely distributed throughout the serogroup B meningococcus genome, two clusters could be identified. The first contained insertions in three genes responsible for iron transport proteins (NMB1728-1730) and the second cluster included insertions in four genes of hitherto unknown function (NMB1954-2006).

With a similar STM approach, four previously uncharacterized genes (NMB0065, NMB0352, NMB0638, and NMB2076) involved in polysialic acid capsule production were found which when mutated rendered a N. meningitidis ser-ogroup C (8013) ST177 IST-18 complex strain serum-sensitive [73]. Due to the screening method used, 14 of the 18 genes identified were important for the synthesis of the polysialic acid capsule or the lipooligosaccharide, suggesting that these genes are likely to be the only meningococcal attributes necessary for serum resistance. However, since the authors only present the sequencing results for the first half of the library, corresponding to 2281 mutants, it may be still too early to draw definitive conclusions.

Unfortunately, the fact that the two isolates used in the STM studies have not been used in other studies of meningococcal biology and are not well-characterized, representative variants of hyperinvasive lineages restricts the value of these results to some degree [74].

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