SummaryMajor pathogenic clonal complexes (cc) of Neisseria meningitidis differ substantially in their point prevalence among healthy carriers. We show that frequently carried pathogenic cc (e.g. sequence type ST-41/44 cc and ST-32 cc) depend on extracellular DNA (eDNA) to initiate in vitro biofilm formation, whereas biofilm formation of cc with low point prevalence (ST-8 cc and ST-11 cc) was eDNA-independent. For initial biofilm formation, a ST-32 cc type strain, but not a ST-11 type strain, utilized eDNA. The release of eDNA was mediated by lytic transglycosylase and cytoplasmic N-acetylmuramyl-L-alanine amidase genes. In late biofilms, outer membrane phospholipase A-dependent autolysis, which was observed in most cc, but not in ST-8 and ST-11 strains, was required for shear force resistance of microcolonies. Taken together, N. meningitidis evolved two different biofilm formation strategies, an eDNA-dependent one yielding shear force resistant microcolonies, and an eDNA-independent one. Based on the experimental findings and previous epidemiological observations, we hypothesize that most meningococcal cc display a settler phenotype, which is eDNA-dependent and results in a stable interaction with the host. On the contrary, spreaders (ST-11 and ST-8 cc) are unable to use eDNA for biofilm formation and might compensate for poor colonization properties by high transmission rates.

Neisseria meningitidis is a commensal of the human nasopharynx occasionally causing invasive disease. In vitro biofilms have been employed to model meningococcal carriage. A proteomic analysis of meningococcal biofilms was conducted and metabolic changes related to oxygen and nutrient limitation and upregulation of proteins involved in ROS defense were observed. The upregulated MntC which protects against ROS was shown to be required for meningococcal biofilm formation, but not for planktonic growth. ROS-induced proteomic changes might train the biofilm to cope with immune effectors.

In Gram-negative bacteria, autotransporter proteins constitute the largest family of secreted proteins, and exhibit many different functions. In recent years, research has largely focused on mechanisms of autotransporter protein translocation, where several alternative models are still being discussed. In contrast, the biogenesis of only a few autotransporters has been studied and, likewise, regulation of expression has received only very limited attention. The glycosylated autotransporter adhesin involved in diffuse adherence (AIDA)-I system consists of the aah gene, encoding a specific autotransporter adhesin heptosyltransferase (AAH), and the aidA gene, encoding the autotransporter protein (AIDA-I). In this study, we investigated the promoter organization and transcription of these two genes using reporter plasmids carrying lacZ transcriptional fusions. The two genes, aah and aidA, are transcribed as a bicistronic message. However, aidA is additionally transcribed from its own promoter. There are two distinct start sites for each of the two genes. Interestingly, transcription of both genes is enhanced in hns and rfaH mutant backgrounds. Furthermore, we addressed the influence of environmental factors and different genetic backgrounds of Escherichia coli K-12 strains on transcription activity. We found that transcription varied considerably in different E. coli K-12 laboratory strains and under different growth conditions.