Question 1: How does Type 11 secretion promote commensal Neisseria survival?
To identify novel host interaction factors, we constructed a transposon library in N. musculi (Nmus), our asymptomatic carriage model organism, and screened this library in mice to find factors essential for host persistence. This screen identified over 400 genes that are required for maintenance of bacterial populations in vivo. Many genes identified in our screen are poorly characterized, underscoring how much we still need to learn about the genetic basis of persistence. We are particularly interested in homologs of Type 11 secretion system (slam) cargoes/effectors, and highly conserved putative surface proteins. We identified an Nmus homolog of slam1 in our screen, along with several hypothetical proteins with high similarity to putative membrane or secreted proteins in human adapted Neisseria. The essentiality of these factors in long term colonization suggests they may play a yet undescribed role in the interaction of Neisseria with its host.
Question 2: How does the commensal polysaccharide capsule impact Neisseria carriage?
The capsular polysaccharide (CPS), considered a virulence factor of Neisseria meningitidis, is also harbored by 13 species of commensal Neisseria, including Nmus. The presence of the CPS locus in commensals raises many questions on the function of these structures within the host, and the evolution of capsular serogroups in Nme associated with invasive infection. Our mutant screen identified several genes in the Nmus CPS locus as essential to persistence. We are interested in defining the structure, biological function, and regulation of commensal CPS to evaluate its contribution to survival on the mucosa.
Question 3: What is the function of the Type IV pilus during commensal-host interaction?
The Type four pilus (Tfp) is a highly conserved host interaction factor encoded across the entire Neisseria genus. This complex assemblage of proteins drives Neisseria motility, adhesion, DNA uptake and initial stages of biofilm formation. We recently demonstrated that Tfp motor and modification proteins are required for colonization and persistence in vivo. Based on these data we are investigating three potentially interconnected facets of Tfp-related host adaptation:
1.Tfp dependent microcolony formation allows Neisseria to withstand shear stress (from fluid flow and peristalsis) on the mucosal surface.
2.Signaling between bacterial cells may be influenced by Tfp retraction, leading to activation of pro-survival transcription pathways necessary for adaptation to the host environment during colonization.
3.Tfp retraction activates host cell pathways in vivo, leading to the creation of pro-survival micro-environments which support establishment of bacterial populations.