Abstract

Unicellular green algal strains, identified as Cosmarium (Chlorophyta), were isolated from Aïn-Echeffa hot spring in north Tunisia. Different extracts (methanol, hexane, acetone, acetone: methanol and water) obtained from both biomass and extracellular polysaccharides (EPS) were evaluated for their antibacterial, antioxidant and cytotoxic activities. First, extracts were tested in vitro for eventual antibacterial activities against a collection of Gram positive and negative bacteria. Most extracts (biomass and EPS) showed significant antibacterial effects, with minimum inhibitory concentrations (MIC) ranging from 28 to 85 µg/ml for biomass and 50 to 150 µg/ml for EPS. Moreover, based on the capacity of each sample to scavenge the ABTS radical cation, we revealed that the EPS aqueous extract presented a moderate antioxidant activity (24.97%). Finally, the toxicity of the biomass extracts was evaluated using the brine shrimp Artemia salina, as test organism. All extracts were identified as non-toxic (LC₅₀ > 400 µg/ml).

Key words: Cosmarium, biomass, extracellular polysaccharides (EPS), cytotoxicity, antibacterial, antioxidant.