Due to its high genetic diversity and its ability to cause life-threatening blood stream infections, N. meningitidis is an excellent model species to study how a high diversity at the genetic level translates into diversity at the phenotypic level, leading to virulence differences among different bacterial strains, and to study the pathogenesis of bacterial sepsis in human ex vivo infection models. A basic assumption for pathogenic bacteria is that virulence is genetically determined by virulence factors encoded in the bacterial chromosome. In fact, it is known that the high genetic diversity observed might not be entirely neutral and may result in phenotypic differences at the transcriptomic and likely metabolic level therefore affecting meningococcal virulence in a strain-dependent manner. Since classical candidate gene-based approaches have failed so far to identify a virulence gene set in N. meningitidis, our group employs the whole spectrum of up-to-date molecular biological and genomic techniques including comparative whole-genome sequencing as well as expression microarrays and RNA-Seq to search in an unbiased manner for genetic virulence determinants in N. meningitidis.
Systems biological analysis of transcriptomic regulation in carriage and invasive strains
For example, a recent systems biology analysis, comparing the transcriptomes from a carried and invasive-associated meningococcus in conditions mimicking infection, indicated that inactivating mutations in amino acid metabolism genes were buffered at the transcriptional level. Consequently, while both meningococci were able to grow in human blood, they showed significant differences in the expression of numerous virulence-associated determinants suggesting that meningococcal virulence was linked to transcriptional buffering of cryptic genetic variation in metabolic genes (Ampattu et al., 2017). These findings raise questions about some of the original concepts of bacterial virulence factors.
Activation of different transcriptional networks in the meningococcal carriage strain α522 and the genetically related yet hyperinvasive strain MC58 upon transition from human saliva to human blood (from Ampattu BJ et al. 2017)
The impact of natural genetic variation in small non-coding RNAs on meningococcal disease
In a joint project with the group of Prof. Dr. J. Vogel from the Institute for Molecular Infection Biology (IMIB) / Helmholtz Institute for RNA-based Infection Research (HIRI) we recently determined the primary transcriptome of Neisseria meningitidis and its interaction with the RNA chaperone Hfq in order to better understand also the role of small non-coding RNAs in meningococcal infection biology (Heidrich et al. 2017). Differential RNA sequencing (dRNA-seq) revealed 65 sRNAs of which 45 were not previously identified, and the expression of over 20 was also confirmed by northern-blot analysis. By combining co-immunoprecipitation of sRNAs bound to the RNA chaperone Hfq with RNA sequencing (RIP-seq) we could further identify a large Hfq-centered post-transcriptional regulatory network comprising 24 sRNAs and 407 potential mRNA targets, and rifampicin treatment experiments demonstrated that Hfq binding confers enhanced stability on sRNAs. Special focus is currently on the further biological characterization of selected bound sRNAs in order to obtain a mechanistic understanding of the contribution of sRNAs to meningococcal virulence.
The Hfq centered network in N. meningitidis connecting regulatory short non-coding RNAs (ellipsoids) with the potential mRNA targets (colored boxes).
For more information about our work with N. meningitidis see the selected references given below and in the publication list.
Selected recent publications
Heidrich N., S. Bauriedl, L. Barquist, L. Li, Schoen C*, and Vogel J* (2017) The primary transcriptome of Neisseria meningitidis and its interaction with the RNA chaperone Hfq. Nucleic Acids Res in press
Ampattu B. J., L. Hagmann , C. Liang, M. Dittrich, A. Schlüter, J. Blom, E. Krol, A. Goesmann, A. Becker, T. Dandekar, T. Müller, and C. Schoen (2017) Transcriptomic buffering of cryptic genetic variation contributes to meningococcal virulence. BMC Genomics 18: 282