A COPPER-TOLERANT PHORMIDIUM SPECIES FROM LAKE MATHEWS, CALIFORNIA, THAT PRODUCES 2-METHYLISOBORNEOL AND GEOSMIN

A benthic Phormidium sp. was isolated in 1988 from Lake Mathews, a source-water reservoir in southern California with a long history of 2-methylisoborneol (MIB) problems. Unialgal cultures were analyzed by salted closed-loop stripping analysis (CLSA) and gas chromatography (GC), which confirmed the presence of MIB at levels of up to 280-mu-g/l. Geosmin was also found at 2-36-mu-g/l. Resurgence of the alga following copper sulfate (CuS04) applications suggested resistance to the algicide. Laboratory experiments showed that the Phormidium was relatively tolerant of copper (surviving at least 3 mg/l of cupric ion after a 1-day exposure) in filtered lake water. The organism also survived 4 mg/l of copper for one day in a variety of sediment samples. This organism was implicated in the longest MIB episode in Lake Mathews, where MIB remained above historical background levels through the winter of 1989-1990. The Phormidium has apparently become the principal MIB producer in Lake Mathews, supplanting Oscillatoria curviceps after 10 years.