Abstract
Several red algae in axenic culture decline in artificial seawater after a period of cultivation. Nemalion helminthoides rapidly loses its brown-red colour and grows with longer and thinner threads. Extracts of contaminated red algae, or nutrient medium in which they have grown, as well as fresh seawater from the Fucus-Ascophyllum zone, enhance growth and restore the pigmentation of the cells. Addition of 40 mg Bacto-Casamino acids per litre of nutrient medium had the same effect. After fractional precipitation with ethyl alcohol and separation on a Sephadex column the activity was localised to a peptide fraction. Results from chromatography point to effects from a low molecular weight substance active alone or coupled to a peptide.