Effects of elevated nitrogen on the growth and geosmin productivity ofDolichospermum smithii

Geosmin is one of the most common earthy-musty odor compounds, which is mainly produced by cyanobacteria in surface water. Nitrogen (N) is an important factor affecting the growth of cyanobacteria and its secondary metabolites production due to the eutrophication. In this study, we compared the effects of elevated N on the growth and geosmin productivity ofDolichospermum smithiiNIES-824 (synonymAnabaena smithiiNIES-824), aiming to better understand the mechanisms involved and give an important and fundamental knowledge to solve off-flavor problem. Results show that elevated N concentration promoted more chlorophyll a (Chl-a) production, whereas the geosmin synthesis decreased, revealing a possible competitive correlation between the Chl-a concentration and geosmin production ofD. smithiiNIES-824. The majority of geosmin (> 90%) was retained intracellularly during the 28 days of cultivation. The qRT-PCR analysis demonstrates that the expression level of the geosmin synthase gene (geoA) was constitutive and decreased at the higher N concentration during the exponential growth phase of cyanobacterial cells. Furthermore, the decrease ofgeoAexpression during the decline phase suggested thatgeoAtranscription was closely related to cell activity and isoprenoid productivity.

Automated summary

Elevated nitrogen concentration can promote chlorophyll a production while inhibiting geosmin synthesis in Dolichospermum smithii NIES-824. The majority of geosmin is retained intracellularly, and the expression of geosmin synthase gene (geoA) is constitutive but decreases at higher nitrogen concentration. The transcription of geoA is closely related to cell activity and isoprenoid productivity, suggesting a regulatory mechanism in geosmin production.