Geniposide, an iridoid glucoside, has been isolated from the butanol fraction of Gardenia jasminoides Ellis (Rubiaceae). The component was found to be transformed into the blue pigments by some aerobic bacteria, suggesting that geniposide is the precursor for the formation of pigments after converting into genipin, an aglycon of geniposide, by ${eta}-glucosidase$. Some bacteria having a ${eta}-glucosidase$ activity did not form the pigments, which may mean that the formation of pigments can only be occurred by the reaction of any enzyme or compound in the pigment-producing bacteria.