Part of a major quorum-sensing system that regulates the development of genetic competence (PubMed:22197102). Involved in the maturation of the competence pheromone ComX (PubMed:22197102, PubMed:25036949). Acts by catalyzing the transfer of a geranyl group on the ComX pheromone (PubMed:22197102, PubMed:25036949, PubMed:31670609). Cannot use farnesyl diphosphate (FPP) (PubMed:31670609). (2E)-geranyl diphosphate + L-tryptophyl-[protein] = (2S,3R)-3-geranyl-2,3-dihydro-2,N(alpha)-cyclo-L-tryptophyl-[protein] + diphosphate Binds 2 Mg(2+) ions per subunit. Optimum pH is 8.0-9.5. Optimum temperature is 37 degrees Celsius. Belongs to the FPP/GGPP synthase family.