A dual role of extracellular DNA during biofilm formation of Neisseria meningitidis

P>Major 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.