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Cyanobacteria is a highly diverse group o f prokaryotes and are recognized as a potent
source o f biologically active compounds with antiviral, antibacterial, antifungal, and
anticancer properties. In the present study, the cyanobacterium Oscillatoria sp. was isolated
from the Senanayaka Samudraya reservoir. Sri Lanka. Methanol crude extract o f Oscillatoria
was used to screen antioxidant (DPPH, ABTS, phosphomolybdenum, nitric oxide scavenging,
and reducing power assay), anti-inflammatory (inhibition o f protein denaturaton) and
cytotoxicity effects (brine shrimp bioassay). The total phenolic and flavonoid contents in the
methanol and n-hexane extracts were determined using Folin-Ciocalteu reagent and aluminum
chloride (AICL) method, respectively. The total phenolic contents (TPC) 43.25 (± 0.03) mg
GAEg'1 extract and total flavonoid contents (TFC) 47.13 (± 0.01) mg qua (quercetin) g '1 o f the
Oscillatiria methanol extract was found to be higher in the n-hexane extract. The total
antioxidant property o f the methanol extract was detected as 13.24 (± 0.01) mg GAE g '1 at
1000 mg L'1. Free radical scavenging properties o f the extract for IC50 was 180 mg L'1 (DPPH)
whereas IC50 values o f nitric oxide scavenging assay was 125 mg L'1. Ferric reducing property
o f the extract was 9.46 (± 0.01) mg GAE g'1 at 1000 mg L'1. Anti-Inflammatory properties o f
the crude extract showed 90.23 (± 1.48)% maximum inhibition at 570 mg L'1 and IC50 value
was found as 288.04 (± 2.78) m g L'1 (r = 0.946) respectively. The lethal concentration o f 50%
o f crude extract against brine shrimp assay at 6. 12 and 24 h were recorded as 2500 , 1250 and
625 mg L’1 respectively. The result o f the study revealed that OsiUatoria sp. contains active
compounds which have the potential for pharmaceutical applications
