Regulation of gene expression in the human pathogen Neisseria meningitidis
remains poorly understood. The meningococcus is a good model for a global
analysis of transcriptional regulation as it has fewer transcriptional regulators
and proteins able to modulate gene expression compared to other species with
genomes of similar size. The genes encoding proteins predicted to modulate
transcription in the meningococcus were identified using a dedicated database
for systematical functional analysis (NeMeSys) in this species and mutated by
utilising an improved in vitro transposon mutagenesis system. The resulting
mutants were subjected to phenotypic analysis for growth and functions linked
to one of the major virulence factors of the meningococcus, Type-four pili (Tfp).
Tfp are essential for adhesion, aggregation, twitching motility and DNA
competence in pathogenic Neisseria species. However, not much is known about
the expression of the 16 proteins essential for Tfp biogenesis, and the seven
proteins playing important roles in Tfp biology. The mutants were assessed for
the Tfp-dependent phenotypes: aggregation, adhesion to human cells and
twitching motility. No mutants were found to be dramatically impaired for these
properties. However, two transcriptional regulators, HexR (NMV_1005) and
FarR (NMV_2033), were found to influence the aggregative abilities of the
meningococcus, with mutations in these genes resulting in a slow aggregating,
and consequently, slow adhering phenotype.
In parallel, two transcriptional regulators were chosen for further
characterisation because they are encoded on genomic islands absent in the nonpathogenic
Neisseria strain, Neisseria lactamica and could thus contribute to
virulence. One island encoded an AraC type regulator divergently transcribed
from genes encoding a putative TonB-dependent iron uptake system, whilst the
other island encoded a putative LysR type regulator divergently transcribed from
a putative transporter. These regulators are likely to require specific inducer
molecules that may be absent from experiments performed in vitro.