Physiological Strategies To Control Geosmin Synthesis in Channel Catfish Aquaculture Systems

Several microbial taxa produce 1α,10β-dimethyl-9α-decalol (geosmin) from farnesyl precursors resulting in an intense musty "off-flavor" that negatively impacts the flavor quality of channel catfish (Ictalurus punctatus) and other food and water resources. Methods to selectively control geosmin production are not available, and the sporadic occurrence of geosmin hinders identification of potential microbial sources of geosmin. Physiological investigations were conducted to provide information necessary to develop molecular controls of geosmin production. Growth of the geosmin-producing filamentous bacterium Streptomyces tendae was inhibited by exogenous farnesol, whereas geosmin did not inhibit growth. Media were identified that both promote and repress geosmin production, and cultures of S. tendae grown on geosmin-promoting media were more resistant to farnesol than cultures grown on media that repress geosmin production, suggesting that geosmin production may provide a mechanism to remove farnesyl moieties. This information is being used to search for non-geosmin producing isolates to competitively exclude problematic strains and to provide sequence information required for gene probes to identify potential sources of geosmin.