Optimization of growth conditions and fatty acid analysis for three freshwater diatom isolates

SUMMARY Diatoms are a group of highly abundant and diverse aquatic algae species. They contain high lipid content along with many bioactive compounds that can be exploited for biotechnological applications. Despite these attractive attributes, diatoms are underrepresented in production projects due to difficulties in their cultivation. To optimize the growth of three freshwater diatom isolates, Cyclotella sp., Synedra sp. and Navicula sp., an orthogonal assay on N, P, Si and Fe, as well as temperature and pH, was designed using traditional single-factor tests. We also studied the effect of using nanosilica as an alternate Si source on growth and found that the diatom isolates studied achieved their highest growth rates under different combinations of nutrient and environmental conditions. Silica had the greatest influence on growth, followed by phosphate and iron. The optimized growth conditions for Synedra sp. were N: 30 mg L −1 , P: 3 mg L −1 , Si: 14.8 mg L −1 , Fe: 0.448 mg L −1 , temperature 25°C and pH 8. For Navicula sp.: N: 20 mg L −1 , P: 2.5 mg L −1 , Si: 19.7 mg L −1 , Fe: 0.112 mg L −1 , temperature 30°C and pH 7.5–8. For Cyclotella sp.: N: 20 mg L −1 , P: 2.5 mg L −1 , Si: 19.7 mg L −1 , Fe: 0.448 mg L −1 , temperature 30°C and pH 7.5–8. Nano silica negatively affected growth in Navicula sp. and Cyclotella sp., but no such effect was observed in Synedra sp. Fatty acid profiling showed C16:0, C16:1( n − 7), C18:0 and C20:5( n − 3) as major fatty acids, with no significant differences in fatty acid methyl ester profiles between traditional and modified media. This work gives us a new insight into the growth requirements of freshwater diatom species, which are less studied than marine species.