Comparative physiology of geosmin production by Streptomyces halstedii and Anabaena sp.

Geosmin and 2-methylisoborneol (MIB) are microbial metabolites that can cause earthy or musty off-flavors in aquatic food animals as well as seasonal taste and odor episodes in drinking water. This paper compares effects of selected environmental factors on biomass and geosmin production by the actinomycete Streptomyces halstedii and the cyanobacterium Anabaena sp., isolated from an aquaculture pond and from a source-water reservoir, respectively. For S. halstedii, optimal biomass production occurred at pH 6-7 and 30°C, and optimal geosmin synthesis occurred at pH 9 and 35°C. Low concentrations of both nitrate- and ammonium-nitrogen favored geosmin production, with higher concentrations stimulating biomass production. For Anabaena sp., optimal biomass production at 20 days occurred at 15°C and a light intensity of 17 μE/m²/s; optimal geosmin synthesis occurred at 20°C and 17 μE/m²/s. Chlorophyll a (chl a)/biomass varied inversely with light intensity. Maximal geosmin/biomass occurred at 20°C (17 μE/m²/s), and geosmin/chl a varied inversely with temperature. It was concluded that at 20°C, increasing light intensity favors lower chl a and greater geosmin synthesis by Anabaena sp.; at 17 μE/m²/s, increasing temperature stimulates chl a production (to 25°C) but represses geosmin synthesis (above 20°C).