Abstract:
Marine red algae have been used in traditional medicine for centuries while the
therapeutic and biological properties of freshwater red algae are almost unknown. The
present study was conducted with the aim of identifying the phytochemical constituents,
the antioxidant and antibacterial activity of freshwater red algae, Batrachospermum sp.,
collected from headwater region of Wathurawa-Ela, in Deniyaya. Methanol and aqueous
extracts of Batrachospermum were subjected to seven qualitative phytochemical
screening tests, and the antioxidant activity for the methanol extract was evaluated using
2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. Further, their
potential antibacterial activity against human pathogenic bacteria, Bacillus cereus and
Escherichia coli were evaluated using Kirby-Bauer disk diffusions test, for both extracts.
Qualitative phytochemical analysis identified the presence of flavonoids, steroids and
alkaloids in both methanol and aqueous extracts while terpenoids and glycosides were
detected only in the aqueous extract. The methanol extract of Batrachospermum showed
an IC50 (half-maximal inhibitory concentration) of 99.70 μg/mL of antioxidant activity
while, the methanol extract of the standard reference, ascorbic acid showed an IC50 of
71.14 μg/mL, indicating its antioxidant activity. The antibacterial activity of methanol
extract tested against B. cereus was moderately strong compared to the inhibition induced
by the solvent (99.8% methanol). The diameter of the inhibition zones was, 10.50±2.12
mm, 11.00±1.41 mm, 7.00±0.00 mm and 10.00±2.83 mm for undiluted (8 μg/mL) and
1:1, 1:2 and 1:4 diluted methanol extracts respectively. For methanol, it was 7.00±0.00
mm. The antibacterial activity of methanol extract against E. coli was weak compared to
the inhibition induced by the solvent in which the diameter of the inhibition zone for
methanol was greater than that of methanol extracts of phytochemicals. The diameter of
the inhibition zones was, 0.00±0.00 mm, 7.00±0.00 mm, 10.00±0.00 mm and 8.00±0.00
mm for undiluted (8 μg/mL) and 1:1, 1:2 and 1:4 diluted methanol extracts respectively.
For methanol, it was 9.50±0.71 mm. Aqueous extracts did not show any inhibition
towards either the bacterial isolates. These results implicate the presence of antibacterial
compounds, phytochemicals, and antioxidants in Batrachospermum that could be a
potential source for medicinal and therapeutic applications.
