Antioxidant and antimicrobial activities in the four species of marine microalgae isolated from Arabian Sea of Karnataka Coast

69-75<span style="font-size:9.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="" lang="EN-US">In the present study, four marine microalgae namely, Chaetoceros calcitrans, Skeletonema costatum, Chroococcus turgidus and <i style="mso-bidi-font-style: normal">Nannochloropsis oceanica were evaluated for their antioxidant and antimicrobial activities. Among the four microalgae, planktonic green alga, Nannochloropsis oceanica showed higher antioxidant potential (340.13 µmol AAE/g DW), radical scavenging activity (13.3 µmol GAE/g DW) and reducing power capacity (86.21 µmol GAE/g DW). Microalgae namely, Skeletonema costatum and Chroococcus turgidus showed chelating ability, whereas Nannochloropsis oceanica and Chaetoceros calcitrans did not. Total phenolic content of microalgae was highly correlated with the antioxidant activity. Methanol, ethanol and hexane extracts were screened for their antimicrobial activities against selective human pathogens. Extracts showed effective inhibitory activity against Staphylococcus aureus, Streptococcus pyogenes and Bacillus subtilis. Hexane extract of Chroococcus turgidus showed significant inhibition (pEscherichia coli followed by ethanol extract of Skeletonema costatum against Streptococcus pyogenes. Antifungal activity was found only in Skeletonema costatum and Chroococcus turgidus. Findings have indicated promising antioxidant and antimicrobial activities of microalgae and they could be used to derive biologically active compounds of nutraceutical potential.