Temperature-dependent FlgM/FliA complex formation regulates Campylobacter jejuni flagella length

Abstract

Regulation of the biosynthesis of the flagellar filament in bacteria containing multiple flagellin genes is not well understood. The major food-borne pathogen Campylobacter jejuni possesses on both poles a flagellum that consists of two different flagellin subunits, FlaA and FlaB. Here we identify the protein Cj1464 as a regulator of C. jejuni flagellin biosynthesis. The protein shares characteristics of the FlgM family of anti-σ factor proteins: it represses transcription of σ28-dependent genes, forms a complex with σ factor FliA, and is secreted through the flagellar filament. However, unlike other FlgM proteins, the interaction of C. jejuni FlgM with FliA is regulated by temperature and the protein does not inhibit FliA activity during the formation of the hook-basal body complex (HBB). Instead, C. jejuni FlgM limits the length of the flagellar filament by suppressing the synthesis of both the σ28- and the σ54-dependent flagellins. The main function of the C. jejuni FlgM therefore is not to silence σ28-dependent genes until the HBB is completed, but to prevent unlimited elongation of the flagellum, which otherwise leads to reduced bacterial motility. © 2010 Blackwell Publishing Ltd.