© by PSP Volume 18 – No 7b. 2009 Fresenius Environmental Bulletin 1363 THE INFLUENCE OF DIFFERENT PHOSPHATE AND NITRATE CONCENTRATIONS ON GROWTH, PROTEIN AND CHLOROPHYLL A CONTENT OF Scenedesmus obliquus Abuzer Çelekli 1* and Muharrem Balcı 2 1,* Department of Biology, Faculty of Art and Science, University of Gaziantep, 27310 Gaziantep, Turkey 2 Department of Biology, Faculty of Arts and Science, University of Istanbul, Turkey ABSTRACT The growth, chlorophyll a and protein production with Scenedesmus obliquus was performed in modified John- son’s medium at initial phosphorus and nitrogen concen- trations of 0.1, 0.3, 0.5, 0.7 (P) and 8, 12, 16 20 mM (N). Initial concentrations of both nutrients had a significant effect (p>0.01) on growth and contents. The highest yield (15.5±0.176 x 10 6 cell mL -1 ), chlorophyll a (10.3±0.157 mg L -1 ), and protein yields (32.3±0.323 mg L -1 ) were obtained with concentrations of 0.3 mM phosphate and 12 mM nitrate. Cell number showed significant correlations with amount of chlorophyll a (p<0.01, r = 0.97) and protein (p< 0.01, r = 0.83). The medium with a 40:1 N/P ratio favored S. obliquus growth. Specific growth rates varied from 0.28 to 0.40 cell divisions d -1 . KEYWORDS: Chlorophyll a, growth, nutrient, Scenedesmus obliquus. INTRODUCTION Microalgae play a key role in aquatic ecosystems and their mass production is of paramount importance in aqua- culture because they are the main food source for larvae of many species of zooplankton, mollusks, crustaceans, and fish [1]. In addition, their biomass contains several com- pounds of high commercial value, such as pigments, essen- tial fatty acids, vitamins and antioxidants [2, 3]. In all cases, their production in commercially-viable quantities depends on the environmental conditions and on their physiologi- cal requirements. For this reason, it is important to deter- mine the optimum culture conditions for the achievement of high yields of microalgae and cyanobacteria in standard media [4, 5]. Because of their adaptability to different environmental conditions and high reproduction, several species of the green algae Scenedesmus spp. (Chlorococcales) have been grown worldwide for industrial purposes [6-8]. In addition, Scenedesmus obliquus is a versatile organism which may be used for domestic and industrial wastewater treatment [5, 9], and its culture has been suggested for oxygen pro- duction in heavy metal removal and for waste products recycling [9-11]. The main factors to be considered in biotechnological research are the potential of each species for industrial aqua- culture purposes and the best culture conditions to obtain suitable amounts of biomass of the desired composition, which necessarily implies the need to investigate the effect of the chemical characteristics of the growth medium [12, 13]. The aim of this work was to determine the optimum conditions for growth, protein and chlorophyll a yields of S. obliquus grown in Johnson’s medium with different phosphate and nitrate concentrations. MATERIALS AND METHODS Microorganism and batch experiments The local strain of the green alga, S. obliquus, isolated from Lake Gölcük and identified according to Komárek and Fott [14] and John et al. [15], was maintained in Johnson’s medium [16] under 2.0 klux continuous light. The compo- sition of the growth medium was MgCl 2 6H 2 O, 1.5 g; KCl, 0.2 g; CaCl 2 2H 2 O, 0.2 g; NaNO 3 , 1.5 g; NaHCO 3 , 0.043 g; KH 2 PO 4 , 0.035 g; 10 mL L -1 Fe solution (Na 2 EDTA, 189 mg L -1 ; FeCl 3 6H 2 O, 244 mg L -1 ), and 10 mL L -1 trace element solution (H 3 BO 3 , 61.0 mg L -1 ; (NH 4 )Mo7O 24 4H 2 O, 38.0 mg L -1 ; CuSO 4 5H 2 O, 6.0 mg L -1 ; CoCl 2 6H 2 O, 5.1 mg L -1 ; ZnCl 2 , 4.1 mg L -1 ; MnCl 2 4H 2 O, 4.1 mg L -1 ). In the first experiment, we determined the growth rate of S. obliquus at different phosphate concentrations (P = 0.1, 0.3, 0.5 and 0.7 mM), and in the second experiment, the cultures were grown with different nitrogen availabil- ities (N = 8, 12, 16 and 20 mM), at that phosphate level which gave the best growth. All experiments lasted 30 days and were in triplicate batch cultures in 250 mL Erlenmeyer flasks with 150 mL of Johnson’s medium. In all cases, the initial inoculum was 5x10 5 cells mL -1 of cultures previously acclimated to each experimental medium. Algal growth was monitored by cell counts with a Thoma hemocytometer, and