In vitro antimicrobial and antioxidant activities of certain brackish water cyanobacteria from Chilika Lake, India

In the present investigation extracts of four species of cyanobacteria, (Pseudanabaena limnetica, Pseudanabaena minima, Anabaena oscillarioides and Oscillatoria princeps) using three solvents namely methanol, acetone and benzene were used to evaluate the pigments and phytochemical constituents, total phenolic, total flavonoid, antibacterial, antifungal and antioxidant activities. The test species possess distinctive amount of carotenoids and phycobiliproteins. The phytochemical screening indicated significant presence of alkaloids, flavonoids, saponins and resin. The antibacterial activity results indicated that, the methanol extract of O. princeps exhibited highest zone of inhibition i.e. 19 ± 1 mm and least MIC value (125 µg/ml) was obtained for Gram-negative pathogens than Gram-positive pathogens (250 µg/ml). The antifungal activity was more prominent in methanol extract of O. princeps against Candida albicans exhibiting higher zone of inhibition (20 ± 2 mm and MIC value 125 µg/ml). The antioxidant activity (DPPH. and ABTS assay) revealed highest activity in methanol extract of O. princeps (79.78% and 71.75%) and lowest was recorded in P. limnetica, (70.45% and 53.17%), while the standard (BHT) was 83.39% for DPPH and 75.04% for ABTS. Likewise, in DPPH assay, the IC50 for O. princeps and A. oscillarioides was (285.98 and 290.19 µg/ml) as compared to BHT (200.00 µg/ml) whereas for ABTS the IC50 was 338.29 and (339.15 µg/ml) against the standard (BHT) 274.07 µg/ml. O. princeps exhibited highest SOD activity as well as protein content (28.4 U/mg and 38.13 mg/g) and lowest was observed in P limnetica (11.8 U/mg and 10.03 mg/g). In GC–MS analysis a total of twelve bioactive compounds were identified in methanol extract of O. princeps. The Methyl-11-Octadecenoate with percentage composition of (28.23%) was the major compound followed by Methyl Hexadecanoate (26.14%). Hence, the present study revealed that cyanobacteria thriving in Chilika lake possess excellent antimicrobial and antioxidants potential and further exploration can open new horizon. © 2021, Society for Plant Research.