S igma factor RpoN (σ 54 ) regulates pilE transcription in commensal N eisseria elongata

Summary Human‐adapted N eisseria includes two pathogens, N eisseria gonorrhoeae and N eisseria meningitidis , and at least 13 species of commensals that colonize many of the same niches as the pathogens. The T ype IV pilus plays an important role in the biology of pathogenic N eisseria . In these species, S igma factor RpoD (σ 70 ), I ntegration H ost F actor, and repressors RegF and CrgA regulate transcription of pilE , the gene encoding the pilus structural subunit. The T ype IV pilus is also a strictly conserved trait in commensal N eisseria . We present evidence that a different mechanism regulates pilE transcription in commensals. Using N eisseria elongata as a model, we show that S igma factor RpoN (σ 54 ), I ntegration H ost F actor, and an activator we name N pa regulate pilE transcription. Taken in context with previous reports, our findings indicate pilE regulation switched from an RpoN ‐ to an RpoD ‐dependent mechanism as pathogenic N eisseria diverged from commensals during evolution. Our findings have implications for the timing of T fp expression and T fp‐mediated host cell interactions in these two groups of bacteria.