Global analysis of transcriptional regulators in Neisseria meningitidis with a focus on two regulators found only in pathogenic Neisseria species

Abstract

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.