Cyanobacteria are abundant producers of natural products well recognized for their bioactivity and utility in drug discovery and biotechnology applications. Novel secondary metabolites from aquatic and terrestrial cyanobacteria are affected by different environmental factors. Cyanobacteria strains from Kermanshah and Golestan province (Iran), where biodiversity is high, are mainly unexplored. Thus, in this research, biological activities (biochemical, antimicrobial, antioxidant, and anti-cancer analyses) of two strains of cyanobacteria, Nostoc sp. N42 and Fischerella sp. S29, were investigated. The amount of total phenols and alkaloids was analyzed using Folin–Ciocalteu assay. Cytotoxic activity was determined compared to liver and lung cancer cells using the MTT assay. The antioxidant activity was determined through the DPPH test and the ABTS assay. Moreover, antimicrobial activity was investigated against gram-positive and gram-negative bacteria using MIC and disk diffusion methods. Results showed that higher amounts of alkaloid (45/33 mg·g-1) and phenol were found in Nostoc sp. N42 and Fischerella sp. Results of cytotoxic activity showed that IC50 methanolic extract of Fischerella sp. S29 against liver cancer was 254.51 mg·mL-1 and against lung cancer was 171.74 mg·mL-1, while IC50 methanolic extract of strain Nostoc sp. N42 against liver cancer was 583.1 mg·mL-1 and against lung cancer was 792.17 mg·mL-1. Moreover, the maximum percentage of the inhibitory effect of antioxidant and antimicrobial activities were found in Fischerella sp. S29 Actually, this strain faces numerous predators in their habitat, and therefore the amount of antibacterial and antioxidant metabolites found in this strain is thought to play an important part in the defense mechanisms to survive. The results of this study prove that cyanobacteria from terrestrial environments have the ability to produce a large number of secondary metabolites to survive in competitive ecological niches.
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