Effects of different phosphorus concentrations in medium on growth, biomass, total phenol contents, and evaluation of antioxidant properties in freshwater cyanobacteria Microcystis aeroginosa andAnabeana variabilis

Phosphorus plays an important role in the growth of algae, production of fatty acids and metabolic processes such as energy transfer and photosynthesis. This study aimed to determine the effect of different phosphorus (P) concentrations on the growth, biomass, phenolic content and antioxidant properties of Microcystis aeroginosa and Anabeana variabilis. After identifying and isolation the desired cyanobacteria, in a completely randomized experimental design was conducted with four different concentrations of Phosphorus in the media, including zero, 0.5, 64 and 256 µgP/L, each in triplicates, using BG11 medium for a 10- day period culture. The average cell density in the treatments of 0 (control), 0.5, 64 and 256 µg/L of P for M. aeroginosa were recorded at 5.2×105, 6.4×105, 10.6×105 and 11.3×105 cells/mL, respectively, for A. variabilis were 2.8×105, 3.4×105, 7.7×105 and 1.4×105 cells/mL, respectively. The amount of total phenolic for M. aeroginosa were 0.5, 1.5, 5.12 and 7.75 mg gallic acid/ DW and for A. variabilis were 4.12, 4.9, 9 and 66.0 mg gallic acid/DW. The DPPH free radical inhibition percentage for M. aeroginosa were equal to 20.51, 22, 23 and 39.23% and for A. variabilis, 25.9, 32.56, 45.12 and 34.1% were calculated. The results showed that the highest growth, photosynthetic pigments and total phenolic as well as antioxidant content were obtained for M. aeroginosa at a concentration of 256 µg/L of P and for A. variabilis at concentration of 64 µg/L of P. Therefore, it can be concluded that the requirement of P in algae is different according to the species, so that each species shows the highest growth rate and other biological activities at a certain concentration of P. Also, understanding the growth of cyanobacteria in relation to the concentration of nutrients in which lead to their bloom is importance for their management of natural water resources, especially fresh and drink waters.