Blue-Green Algae in Lake Biwa Which Produce Earthy-Musty Odors

Since 1969, earthy-musty odor problems have frequently occurred in the water supply system of Kyoto City. Though the causes of these off-flavors were identified as 2-methylisoborneol (MIB) and geosmln, the causative organisms were not identified until recently. Now three species of planktonic blue-green algae from Lake Biwa have been identified as playing important roles in such problems. From the unlalgal culture of each alga, Anabaena macrospora Klebahn was shown to produce geosmln, and both Phormidium tenue (Meneghini) Gomont and Oscillatoria tenuis Agardh to produce MIB. These odorous compounds were found to be mainly stored in trlchomes, although it was once thought that they were dissolved in the surrounding water. Therefore, most of the odorous compounds can be removed from the water when the causative algae are removed.