The diatoms collected and isolated from the Yumurtalık Bay at Northeastern Mediterranean at Gulf of Iskenderun, and species were cultivated under laboratory conditions, identified using molecular techniques, and their growth and biochemical composition were investigated. Sampling was carried out using a plankton nets having 20 μm and 55 μm mesh size for 10 minutes at different depths, horizontally. Salinity, temperature and pH were measured with a YSI model salinometer at each station. The isolation of the required species were done by serial dilutions and applying agar plating methods. Isolated diatom species were cultured in the different media. To purify the species, antibiotic (Ampicillin sodium and Kanamycin) media were used at 5 different rates (200 mg/L, 400 mg/L, 600 mg/L, 800 mg/L, 1000 mg/L). At the same time, acid/base treatment (pH2, pH3, pH4, pH5, pH9, pH10 and pH11) were applicated to the samples. These cultures were maintained at room temperature (20±1°C) under 40 µmol photon m-2s-2 light intensity at 12:12-h light/dark cycle and were aerated continuosly. Isolates were identified morphologically. Isolated diatom species were detected following morphological and molecular identification. Genomic DNA extractions were performed with a DNeasy Plant Mini Kit (Qiagen, Tokyo, Japan) following the manufacturer’s protocol. Then DNA isolated from the cells was and amplified by PCR. Identifications of the species were made with phylogenetic analyses depending on nucleotide sequences of small subunit of nuclear ribosomal DNA. Nucleotide sequencings were performed commercially by Macrogen Inc. (Korea) with the same primers used for PCR amplifications. To evaluate the phylogenetic relationships among isolates Neighbor-Joining (NJ) were used. Experiments were carried out by cultivation of 104 cells mL-1 of Chaetoceros sp. and Nitzschia sp., in 1 L cylinder tubes containing sterilized Si-F/2 medium with a salinity of 30 ppt. The specific growth rate and biomass and biomass productivity, cell density, chlorophyll a, total carotenoid, protein, carbohydrate, lipid and lipid productivity, fatty acid methyl esters (FAMEs) and fucoxanthin contents were determined and showed significant differences (p<0.05) between these two species. The best growth and biochemical composition were obtained from the diatom Chaetoceros sp., while the highest amount of fucoxanthin was found in Nitzschia sp.
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