Interaction of nitrogen and silicate fluctuations with salt stress on growth, and lipid production in Navicula sp.

Diatoms have been recognized as source of important and applicable ingredients such as pigments and essential lipids. In this study, the effects of nitrogen and silicate changes accomplished by salt stress were investigated to analysis the chl a and chl c1+c2 contents, specific growth rate, total lipid percentage and fatty acid composition of Navicula sp. Samples were collected using by plankton net (30-micron pores) in spring 2019, from 6 stations in the Persian Gulf, Iran. In this study, samples were cultured under salt stress (control, 20ppt and 45ppt) and nutrients fluctuation (control: N: 0.5 mg, Si:0.3 mg, high nutrient culture: N:0.9 mg, Si:4.5 mg and without nutrient culture). There was a considerable decrease in dry weight and maximum growth rate under 45ppt salt treatment without silicate. The amount of chl a was not significantly changed under various treatments. The highest level of chl c1+c2 was related to 20ppt with nitrate (3.05 mg L-1) and the lowest value was 0.38 mg L-1 for 20ppt with silicate treatment. The highest level of total lipid content was obtained at 45ppt without silicate. Lipid composition analysis under 45ppt without silicate showed a significant increase (2.07 times compared to control) of palmitoleic acid (C16:1n-7) and trace amounts of polyunsaturated fatty acids were detected. Based on these results, it could be suggested that salt stress without silicate has an important effect to accumulate valuable lipids in Navicula sp. so that, they could be useful in medical and bioenergy applications.