Systematic functional analysis reveals that a set of seven genes is involved in fine-tuning of the multiple functions mediated by type IV pili in Neisseria meningitidis.

Type IV pili (Tfp), which mediate multiple phenotypes ranging from adhesion to motility, are one of the most widespread virulence factors in bacteria. However, the molecular mechanisms of Tfp biogenesis and associated functions remain poorly understood. One of the underlying reasons is that the roles played by the numerous genes involved in Tfp biology are unclear because corresponding mutants have been studied on a case-by-case basis, in different species, and using different assays, often generating heterogeneous results. Therefore, we have recently started a systematic functional analysis of the genes involved in Tfp biology in a well-characterized clinical isolate of the human pathogen Neisseria meningitidis. After previously studying 16 genes involved in Tfp biogenesis, here we report the characterization of 7 genes that are dispensable for piliation and potentially involved in Tfp biology. Using a battery of assays, we assessed piliation and each of the Tfp-linked functions in single mutants, double mutants in which filament retraction is abolished by a concurrent mutation in pilT, and strains overexpressing the corresponding proteins. This showed that each of the seven genes actually fine-tunes a Tfp-linked function(s), which brings us one step closer to a global view of Tfp biology in the meningococcus.