Attached
Cyanobacteria is a group of prokaryotic organisms originally found in the world and are
recognized as a potent source of biologically active compounds with antiviral,
antibacterial, antifungal, and anticancer properties. In the present study cyanobacterium
Lyngbya sp. was isolated from a freshwater reservoir in Sri Lanka and pure
monocultures and mass cultures were prepared. Following growth curve of the
cyanobacterium Lyngbya sp. cells were harvested after 15 days of incubation at
exponential growth. Extraction was carried out by hexane, methanol and
dichloromethane respectively following standard methods. Antioxidant activity of three
solvent extracts were determined using DPPH (1,1-Diphenyl- 2- picrylhydrazyl) assay,
ABTS assay, phosphomolybdenum assay. The total phenolic and flavonoid content in
the hexane, methanol and dichloromethane extracts were determined using FolinCiocalteu reagent and aluminum chloride (A1C13) respectively where antibacterial
activity of different concentration (40 mg/mL, lmg/mL and 0.5mg/mL) of crude extract
was carried out by disc diffusion methods against gram positive bacteria Methicillinresistant Staphylococcus aureus (MRSA) ATCC 25923 and gram negative bacteria,
Pseudomonas aeruginosa ATCC 25853, Salmonella typhii and Escherichia coli ATCC
25922 respectively. Minimum inhibition concentration (MIC) was determined by TTC
bio assay. The highest total phenolic (238.48 ± 0.01 mg GAE/g extract) and flavonoid
content (TFC) (202.53± 0.01 mg qua (quercetin) /g) was recorded in the methanol
crude extract and the concentrations were significantly high compared with the nhexane (p > 0.05) and (p > 0.05) dichloromethane extract. The total antioxidant property
of methanolic extract in phosphomolybdinum assay was 67.24 ± 0.01 mg GAE/g at
1000 mg/L. The highest free radical scavenging activity was detected in the methanol
extract (IC50= 0.053 mg/ml) whereas 0.200 mg/mL and 0.320 mg/mL in hexane and
dichloromethane extract were detected. The results of the ABST antioxidant assay
showed that the highest antioxidant activity in methanol extract (IC50 0.031 mg/ml)
and, in hexane and dichloromethane the antioxidant activities were 0.100 mg/mL and
0.105 mg/mL respectively. The antibacterial activity of methanol extract against only S.
typhii was detected in disc diffusion method and the mean diameter of inhibition zone
was around 18 ± 2 mm in 40 mg/mL and 15 ± 2 mm in 1 mg/ml and 10 ± 2 mm for 0.5
mg/mL respectively within 24 hrs. MIC in the methanol crude extract was 150 mg/L
against S. aureus. Thus, the result of the study showed that the Lyngbya sp. contained
compounds which are potential for pharmaceutical invention and isolation of active
ingredients from the crude extracts are being to progress.
