Abstract
The multidomain (B-NG) protein FlhF, a flagellar biogenesis regulator in several bacteria, is the third paralog of the signal recognition particle (SRP)-GTPases Ffh and FtsY, which are known to drive protein-delivery to the plasma membrane. Previously, we showed that FlhF is required for Bacillus cereus pathogenicity in an insect model of infection, being essential for physiological peritrichous flagellation, for motility, and for the secretion of virulence proteins. Among these proteins, we found that the L2 component of hemolysin BL, one of the most powerful toxins B. cereus produces, was drastically reduced by the FlhF depletion. Herein, we demonstrate that B. cereus FlhF forms GTP-dependent homodimers in vivo since the replacement of residues critical for their GTP-dependent homodimerization alters this ability. The protein directly or indirectly controls flagellation by affecting flagellin-gene transcription and its overproduction leads to a hyperflagellated phenotype. On the other hand, FlhF does not affect the expression of the L2-encoding gene (hblC), but physically binds L2 when in its homodimeric form, recruiting the protein to the plasma membrane for secretion. We additionally show that FlhF overproduction increases L2 secretion and that the FlhF/L2 interaction requires the NG domain of FlhF. Our findings demonstrate the peculiar behavior of B. cereus FlhF, which is required for the correct flagellar pattern and acts as SRP-GTPase in the secretion of a bacterial toxin subunit.
Highlights
Bacillus cereus is a Gram-positive, motile, and spore-forming rod that is ubiquitously found in a wide range of environments including soil, water and foods
The bacterial adenylate cyclase two-hybrid (BACTH) approach was applied to investigate whether FlhF forms dimers in B. cereus
In the case of FlhF/FlhF interaction, Cya could be restored, cyclic adenosine monophosphate synthesized, and the maltose operon genes as well as the cAMP-reporter gene β-galactosidase expressed in the E. coli BTH101 strain
Summary
Bacillus cereus is a Gram-positive, motile, and spore-forming rod that is ubiquitously found in a wide range of environments including soil, water and foods. The secretion of tissue-destructive exoenzymes and toxins, e.g. hemolysins, phospholipases, trimeric toxins, cytotoxins and proteases (Ramarao and Sanchis, 2013; Ehling-Schulz et al, 2019), is of crucial importance in B. cereus pathogenicity. Among these factors, the tripartite hemolysin BL (HBL), consisting of a binding component (B) and two lytic components (L1 and L2), plays a Functional Characterization of Bacillus cereus FlhF primary role in diarrheal food poisoning and necrotizing infections such as endophthalmitis, due to its vascular permeability, hemolytic, and enterotoxic activity (Beecher et al, 1995a,b). Failure to secrete HBL was demonstrated in aflagellated B. cereus natural isolates (Ghelardi et al, 2007) and in an acrystalliferous Bacillus thuringiensis (i.e. B. cereus) mutant for the Type-III flagellar export apparatus (Ghelardi et al, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
