Part of a major quorum-sensing system that regulates the development of genetic competence (PubMed:25855042, PubMed:29665236). Involved in the maturation of the competence pheromone ComX (PubMed:25855042, PubMed:29665236). Acts by catalyzing the transfer of a farnesyl group on the ComX pheromone (PubMed:25855042, PubMed:29665236). In vitro, can also catalyze the farnesylation of single tryptophan and tryptophan derivatives (PubMed:29665236). (2E,6E)-farnesyl diphosphate + L-tryptophyl-[protein] = (2S,3R)-3-farnesyl-2,3-dihydro-2,N(alpha)-cyclo-L-tryptophyl-[protein] + diphosphate Binds 2 Mg(2+) ions per subunit. kcat is 0.18 sec(-1) with [53-73]ComX as substrate. Belongs to the FPP/GGPP synthase family.