Environmental and nutritional factors affecting geosmin synthesis by Anabaena SP.

A cyanobacterium isolated from a source-water reservoir during a spring odor and taste episode and identified as Anabaena sp. consistently produced geosmin during laboratory culture on modified BG-11 liquid medium. Maximal geosmin/biomass occurred at 20°C and a light intensity of 17 μE/m2/s; geosmin/chl a values directly correlated with increasing light intensity (r2=0.95, P<0.01). It was concluded that at 20°C, increasing light intensity favors less chl a synthesis and higher geosmin synthesis; at 17 μE/m2/s, increasing temperature stimulates chl a production (to 25°C) while repressing geosmin synthesis (above 20°C). Nutritional factors promoting biomass, chl a, and geosmin synthesis by Anabaena sp. were also investigated. For cultures grown at 17 μE/m2/s and 20°C for 20 days, both ammonium-N and nitrate-N generally enhanced the growth of Anabaena sp. Nitrate-N promoted more chl a production (r2=0.99) than ammonium-N. Geosmin synthesis was directly correlated with ammonium-N concentrations (r2=0.89), with low nitrate-N (123.5 μg/l) favoring maximal geosmin production (2.8 μg/l). Increasing nitrate-N concentrations promoted a three-fold increase in chl a content with geosmin synthesis decreased by two-fold. Geosmin/mg biomass was directly related to ammonium-N concentration; high nitrate-N levels suppressed geosmin production. No geosmin was detected at or below 118 μg phosphate-phosphorus/l. Geosmin, dry weight biomass, and chl a production were correlated with increasing phosphorus (P) concentration (r2=0.76, 0.96 and 0.98, respectively). No geosmin was detected when copper was present in growth media at or above 6.92 μg Cu2+/l (CuSO4•5H2O). Dry weight biomass and chl a production were negatively correlated with Cu2+ ion concentrations.