The widespread second messenger molecule cyclic-di-GMP (cdG) regulates the transition from motile and virulent lifestyles to sessile, biofilm-forming ones in a wide range of bacteria. Many pathogenic and commensal bacterial-host interactions are known to be controlled by cdG signalling. While the biochemistry of cyclic-dinucleotide metabolism is well understood, much remains to be discovered about the downstream signalling pathways that induce bacterial responses upon cdG binding. As part of our ongoing research into the role of cdG signalling in plant-associated Pseudomonas species, we carried out an affinity-capture screen for cdG binding proteins in the model organism P. fluorescens SBW25. The flagella export AAA+ ATPase FliI was identified as a result of this screen, and subsequently shown to bind specifically to the cdG molecule, with a KD in the low micromolar range. The interaction between FliI and cdG appears to be very widespread.

 

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