Response of growth, protein and fatty acid content of Desmodesmus cuneatus to the repletion and depletion of nitrogen

Introduction : biomass and biochemical composition content (particular fatty acid profile, protein, pigment) play an important role in commercial scale production of microorganisms. nitrogen concentration is the most effective factor in biochemical composition and growth rate changes. materials and method s: the unicellular fresh water microalgae, desmodesmus cuneatus ( scenedesmaceae , chlorophyta), was grown on bm medium under various concentration of nitrogen at 25 c and ph 7.0in a period of 12 days . daily cell counting was done using neubauer haemocytometer to determine the growth rate, cell density and exponential time. the grown cells were harvested in the stationary phase to determine fatty acid and protein content. results : the maximum growth rate ( 0.35 ± 0.09 day−1) and cell density ( 36.00 ± 1.01 ×105 cell.ml-1) was achieved in 2.5 mm of nitrogen concentration . the maximum level of pufa, was 25.31 % of the total fatty acids under n-sufficient conditions (5 mm nitrogen) compared to 17.01 % under n-free. the maximum precentage of protein content ( 36.81 %) was found at 5 mm nitrogen content and minimum ( 11.14 %) was seen at nitrogen free medium . discussion and conclusion : the results showed that control of nutrients plays an important role in microalgae culture. any increase or decrease, depending on the type of nutrient, causes metabolic changes as well as changes in physiology and the nutritional value of microalgae. the nitrogen concentration of 2.5 mm may be more beneficial than other concentrations, as cell number is sustained in exponential phase longer.