Effect of phosphorus deficiency or starvation on the growth, body composition and fatty acid profile of freshwater microalgae Desmodesmus sp.

In this study, the effect of lack and phosphorus deficiency (dipotassium phosphate; K2HPO4) on the growth rate, biomass, biochemical content, and fatty acid profile of Desmodemus sp. was investigated for 14 days. Accordingly, Desmodesmus microalgae were grown in culture media containing no phosphorus (P0), 10 (P10), 20 (P20), 30 (P30), and 40 mg/liter (P40). The P40 treatment was considered as a control group that had the amount of phosphorus required in the standard culture medium BG11. Based on the results, the highest cell density, specific growth rate, and biomass production were simultaneously recorded in the P20, P30, and P40 treatments on the 14th day of culture, which showed a significant difference from the other two groups (P<0.05). In addition, the highest chlorophyll a was also recorded in these three groups, which showed a significant increase compared to the group without phosphorus (P<0.05). The lowest chlorophyll b was recorded in P0 (1.62 mg/L) compared to other experimental groups (P<0.05). The analysis of body composition showed the highest amount of lipid productivity (14.93 mg/liter per day) in P20 treatment, which has a significant difference with other experimental groups, except for P10 (13.17 mg/liter per day) (P<0.05). The highest protein productivity rate was measured in P30 and P40 groups (P<0.05) and the highest carbohydrate productivity rate (10.55 mg/L per day) was measured in P40 without significant difference with P30 (8.87 mg/l per day). The highest amount of saturated fatty acids was observed in P0 (47.66% of total fat) and the highest long-chain unsaturated fatty acids in P40 treatment (30.58% of total fat) without significant difference with P30 (29.33% of total fat). Based on the results, the concentration of 20 mg/liter of phosphorus is a suitable concentration for the cultivation of Desmodesmus sp. microalgae for the production of biofuel, while the concentration of 40 mg/liter of phosphorus is a suitable concentration for the cultivation of the microalgae for using in the food and aquafeed industries.