<jats:title>Abstract</jats:title> <jats:p>Bacillus subtilis subsp. natto produces poly-γ-glutamic acid under the control of quorum sensing. We identified ComXnatto pheromone as the quorum-sensing pheromone with an amino acid sequence of Lys-Trp-Pro-Pro-Ile-Glu and the tryptophan residue posttranslationally modified by a farnesyl group. ComXnatto pheromone is unique in the sense that the 5th tryptophan residue from the C-terminal is farnesylated.