Background: This study describes the evaluation of antimicrobial, antialgal and cytotoxic activities of crude extracts from cyanobacterial strains isolated from rhizospheric and freshwater environment.Methods: Four cyanobacterial strains were isolated from freshwater and rhizospheric samples collected from various sites of University of the Punjab, Lahore, Pakistan. Selected strains were identified by 16S rDNA ribotyping as species of genera, Cyanothece (CY1), Synechococcus (CY2), Leptolyngbya (CY3) and Synechococcus (CY4). The organic extracts i.e., methanolic, ethanolic and acetonic of selected cyanobacterial strains were checked for antibacterial and cytotoxic activity. Antibacterial and antialgal activities of cyanobacterial extracts were determined against, four Gram positive and three Gram negative bacteria using Muller-Hinton (MH) agar well diffusion assay and two algal species using 96-well microtiter plate respectively. Cytotoxic activity was determined against Vero cells and Huh-7 cells.Results: The results showed that all cyanobacterial extracts showed activities against Gram positive bacteria while some of the extracts showed activity against Gram negative bacteria. Acetonic extract of CY4 and CY2 showed moderate discoloration against Chlamydomonas sp. and Chroococcus sp. respectively. In cytotoxicity bioassay, methanolic extracts of strain CY1 and CY2 were most active with an IC50 of 0.625 mg/ml against Vero cells while acetonic extract of strain CY1 showed highest activity against Huh-7 cells (p<0.05).Conclusion: The data of current study conclusively suggest that selected cyanobacteria may be an excellent source for further fractionation to obtain novel antibacterial, antialgal and anticancer substances.Keywords: Cyanobacteria; MTT bioassay; Microtiter plates; Antimicrobial activity; Cytotoxicity
