Chemical composition, fatty acid profile and molecular changes derived from nitrogen stress in the diatom Chaetoceros muelleri

•Chaetoceros muelleri cultured in 0.18 mM NaNO3 did not lose biomass.•Nitrogen deficiency (0.18 mM NaNO3) increased total lipid and carbohydrate content.•Nitrogen deficiency (0.18 mM NaNO3) increased saturated fatty acids.•Nitrogen deficiency (0.18 mM NaNO3) decreased polyunsaturated fatty acids.•DGAT2 and NRT2 expression levels increased with nitrogen deficiency (0.18 mM NaNO3). Microalgae have great potential as biofactories for producing a wide variety of valuable products. Under stress conditions, it is well-known that microalgae accumulate various organic compounds. However, there is little information on the response of the diatom Chaetoceros muelleri to different nitrogen concentrations. In the present study, C. muelleri was grown in medium containing different concentrations of nitrogen (NaNO3; f: 1.76 mM, f/4: 0.44 mM, f/10: 0.18 mM, and 2f: 3.53 mM) and their proximal composition, fatty acid profile, and gene expression (AMT1, PTD9, GltD, DGAT2, and NRT2) compared. The results showed no significant differences in biomass content among nitrogen treatments. Treatment f/10 significantly increased accumulation of lipids and carbohydrates but lowered the concentration of proteins. This treatment also produced shorter-chain fatty acids and a low percentage of polyunsaturated fatty acids, demonstrating the potential of this medium for growing microalgae with a suitable fatty acid profile for biodiesel production. Furthermore, DGAT2 and NRT2 expression was highest at lower nitrogen concentrations, suggesting these genes could be important for modulating lipid biosynthesis in response to nitrogen limitation.