Studies on the earthy-musty odours in natural water (IV). Mechanism of earthy-musty odour production of actinomycetes.

Many reservoirs for water supply have been troubled with earthy-musty odour compounds--2-metylisoborneol (2-MIB) and geosmin. Both of these compounds are terpenoid and related to the metabolite of L-methionine. An experiment using [CD3]methionine and [14CH3]methionine showed that the C-2 methyl group in 2-MIB originate from L-methionine. In the incubation experiment with 10-1000 mg/l of L-methionine, 2-MIB and geosmin appeared in the earlier stages, in greater amounts than in the control. The maximum production of 2-MIB and geosmin increased considerably in the experiments with 10 and 100 mg/l of L-methionine. The effective time for L-methionine addition was after 1 d. Additions after 3 and 5 d were similar to the control. In the incubation experiment with 10-1000 mg/l of folic acid, 2-MIB and geosmin increased only during the 1000 mg/l addition. There seems to be little doubt that L-methionine takes part in the metabolism of 2-MIB and geosmin.