Growth, lipid content, and fatty acid profile of freshwater cyanobacteria Dolichospermum affine (Lemmermann) Wacklin, Hoffmann, & Komárek by using modified nutrient media

In this study, Dolichospermum affine was cultivated under starvation and limitation conditions, using six different concentrations of nitrate (NaNO₃) and phosphate (K₂HPO₄) in BG-11 medium. The biomass, pigments, proteins, carbohydrates, lipids, triacylglycerol-TAG, and fatty acid responses to different modified media were examined in terms of cell density, dry biomass, optical density, growth rate, chlorophyll-a, carotene content, and lipid productivity. Molecular characterization of D. affine isolates was performed using Fourier transform–infrared spectroscopy (FT-IR) and polymerase chain reaction (PCR). In the 20-day batch culture period, one of the modified media, %50 N and P limitation (N-PLᵢₘᵢₜₐₜᵢₒₙ), exhibited higher values than the others in terms of cell density (1.41 × 10⁷ cells/mL), dry biomass (1.68 gL⁻¹), optical density (1.26), growth rate (0.48 day⁻¹), chlorophyll-a (3.76 μg L⁻¹), and total carotenoid (12.99 μg L⁻¹). The maximum percentage lipid content of D. affine was obtained in the control group at 10.67%. Fatty acid profiles have been investigated in six conditions and consisted of 10 fatty acids. The basic saturated fatty acid palmitic acid was (C16:0) for all conditions, and its rate was 40.61% for starvation of N and P (N-PDₑₚᵣᵢᵥₐₜᵢₒₙ) conditions. Oleic acid (C18:1) rate was detected in all groups, but the highest rate was found in the control group with 33.72%. In all conditions, TAG values were found similar, but the highest value was determined at 50% P and 100% N (PLᵢₘᵢₜₐₜᵢₒₙ-NCₒₙₜᵣₒₗ) (27.5%) modified media. Carbohydrate content (20.37%) was found to be high under N and P starvation (N-PDₑₚᵣᵢᵥₐₜᵢₒₙ), while protein content (66.92%) was high under 50% N and 100% P (NLᵢₘᵢₜₐₜᵢₒₙ-PCₒₙₜᵣₒₗ) conditions. The results obtained from this study showed that nitrogen and phosphorus starvation and limitation affecting the biomass, valuable secondary metabolites and lipid accumulation and affected the fatty acid composition of D. affine cultures.