Effect of nitrogen concentration on the growth rate and biochemical composition of the microalga, Isochrysis galbana Mohammad Javad Zarrinmehr a , Omidvar Farhadian a,⇑ , Fatemeh Paykan Heyrati a , Javad Keramat b , Eleni Koutra c , Michael Kornaros c , Ehsan Daneshvar d a Department of Natural Resources, Isfahan University of Technology, Isfahan 84156, Iran b Department of Food Science and Technology, College of Agriculture, Isfahan University of Technology, Isfahan 84156, Iran c Laboratory of Biochemical Engineering & Environmental Technology (LBEET), Department of Chemical Engineering, University of Patras, 26504 Patras, Greece d Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland article info Article history: Received 17 September 2019 Revised 7 November 2019 Accepted 8 November 2019 Available online xxxx Keywords: Nitrogen Isochrysis galbana Growth rate Biochemical composition Fatty acids abstract Nitrogen represents a critical macronutrient that regulates the metabolism and consequently, the growth and biochemical composition of microalgae. In this study, the effect of different nitrogen concentrations (0, 36, 72, 144 and 288 mg/L) on the growth rate and biochemical composition of Isochrysis galbana was investigated. Cell growth, pigments and protein content of I. galbana biomass decreased with diminishing nitrogen concentration; while carbohydrates showed the highest value, 47%, in case of total nitrogen deprivation. Poly unsaturated fatty acids (PUFAs) increased five-fold under sufficient nitrogen concentra- tions (72 mg/L), compared to nitrogen deprivation. In contrast, concentration of saturated fatty acids (SFAs), 75.79% under nitrogen deprivation, was higher than in case of nitrogen sufficiency, 36.63%. The highest carbohydrate, protein and lipid productivities observed were 156.7, 326.2 and 264.6 mg/L under nitrogen concentrations of 72, 0 and 72 mg/L, respectively. The results of this study indicate that nitrogen concentration significantly affects the growth and biochemical compositions of I. galbana. Ó 2019 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Introduction Microalgae as unicellular microorganisms have unique features such as fast growth rate, conversion of light energy to biochemical compounds, biofixation of CO 2 and consumption of organic and inorganic, macro- and micronutrients (Daneshvar et al., 2018). Microalgae can be cultivated in a wide range of aquatic environ- ments with different salinity levels, from fresh water to marine water (Wang et al., 2014a,b), as well as different type of waste waters. Depending on their growth rate, biochemical composition, and special features microalgae can be used as a source of nutrients in feeding human, animal, and in aquaculture (Napolitano et al., 1990). Furthermore, it has been used for pharmaceuticals (as source of bioactive molecules and toxins), cosmetics (due to their pigments and antioxidant properties), energy (through biomethane, biodiesel and biohydrogen production) and for environmental purposes (waste water treatment and CO 2 seques- tration) (Tebbani et al., 2014). The main factors that affect cultivation of microalgae include environmental (light, temperature, pH, nutrient supply and salin- ity) and physical (agitation) conditions, biological parameters, spe- cies of algae and the shape of cultivation container. These aforementioned parameters affect the photosynthetic activity, bio- mass productivity, physiological and biochemical composition of microalgae (Tebbani et al., 2014). Nitrogen as a critical element and a component of high value biological macromolecules, such as proteins, chlorophylls and DNA, plays a fundamental role in microalgal cultivation. Changes in nitrogen concentration can affect growth rate, as well as protein, lipid, and carbohydrate synthesis in microalgae (Pancha et al., 2014). Several studies demonstrated that although nitrogen limita- tion enhances lipid accumulation, it leads to lower biomass pro- ductivity (El-Kassas, 2013). The important issue is harvesting the highest amount of biomass along with the highest amount of main energy storage compounds (Li et al., 2008). Many studies have con- firmed that nitrogen starvation changes biochemical composition, such as carbohydrate and protein, pigments and lipid content, fatty acids composition, as well as photosynthetic activity of microalgae https://doi.org/10.1016/j.ejar.2019.11.003 1687-4285/Ó 2019 National Institute of Oceanography and Fisheries. Hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer review under responsibility of National Institute of Oceanography and Fisheries. ⇑ Corresponding author. E-mail address: omfarhad@cc.iut.ac.ir (O. Farhadian). Egyptian Journal of Aquatic Research xxx (xxxx) xxx Contents lists available at ScienceDirect Egyptian Journal of Aquatic Research journal homepage: www.sciencedirect.com/locate/ejar Please cite this article as: M. J. Zarrinmehr, O. Farhadian, F. P. Heyrati et al., Effect of nitrogen concentration on the growth rate and biochemical compo- sition of the microalga, Isochrysis galbana, Egyptian Journal of Aquatic Research, https://doi.org/10.1016/j.ejar.2019.11.003