ComFB bound to c-di-GMP reduces swimming speed and tumbling frequency in B. subtilis

ComFB is encoded in the comF operon of Bacillus subtilis, situated between the genes for ComFA and ComFC. The latter two proteins are essential for natural transformation, whereas ComFB is dispensable. We show here that ComFB binds specifically and with high affinity to the second messenger c-di-GMP and that ComFB acts as a c-di-GMP receptor to inhibit swarming and swimming motility, apparently by interfering with flagellar activity. We show further that in the absence of ComFC, swarming is completely abrogated by a mechanism that requires FB. These results reveal a new c-di-GMP regulatory system that controls motility independently of MotI.