Antibiotic substances produced by a marine green alga, Dunaliella primolecta

Abstract From among 84 marine algae, the green alga, Dunaliella primolecta C-525, exhibiting the highest antibiotic activity, was selected. A crude extract from this alga strongly inhibited the growth of Staphylococcus aureus, Bacillus cereus, Bacillus subtilis and Entrobacter aerogenes . From experiments on pH, solvent, and an inhibitor of the crude extract of this alga, the antibiotic substance in the algal cells was observed as a base-stable, nonprotein material. To purify this antibiotic substance, a methanol extract of this alga was eluted successively on a DEAE-Sepharose Cl-6B, silica and Sephadex LH-20 gel column. Three peaks exhibiting antibiotic activity from the final column were observed, indicating peak No. 1 to have a molecular weight of over 1300 and peaks Nos 2 and 3 to have molecular weights of about 300–400. The main fractions X, Y and Z of the three peaks were investigated for temperature stability. The activities of fractions X and Z were stable up to 80°C, whereas the activity of fraction Y was unstable above 40°C. The above results indicate that algal cells of D. primolecta contained a number of different antibiotic substances.