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

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Abstract
Many reservoirs for water supply have been troubled with earthy‐musty odour compounds—2‐methylisoborneol (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.