Title: In vitro antibacterial activity of fucoidan isolated from Ascophyllum nodosum and Laminaria digitata

Both Iceland and China have big seaweed resources. In China the utilization is diversified but in Iceland most of the harvested seaweed go to alginate production. In both countries the products are of relatively low value. However, seaweed is composed of different molecules some of which are of high value e.g. fucoidan. Fucoidan has several interesting bioactivities including antibacterial effect. Increasing resistance of bacteria to available antibiotics calls for new and novel antibacterial compounds. One aim of this study was to extract fucoidan from Icelandic local seaweed species (Ascophyllum nodosum and Laminaria digitate) and to optimize the extraction conditions. Another objective was to determine the antibacterial activity of the isolated fucoidans. The results showed that the fucoidan content was 4.7-5.6% of dry weigh in Ascophyllum nodosum and 2.1-3.6% of dry weight in Laminaria digitate depending on reaction conditions. The amount of fucoidan in Icelandic brown seaweed is higher than reported in seaweed harvested in China but lower than reported from the UK. The fractions were isolated through anion-exchange chromatography DEAE-52. The fucoidan from Ascophyllum nodosum showed two main fractions whereas fucoidan from Laminaria digitate had three main fractions. The fucoidan showed inhibitory effect on S.aureus but not on E.coli nor B.subtilis in nutrient broth without salt. However when 1% NaCl was added, B.subtilis was slightly inhibited and the addition of salt enhanced the inhibitory effect on S. aureus. The inhibitory effect of fucoidan from Laminaria digitate was stronger than fucoidan from Ascophyllum nodosum. This is the first study to show that fucoidan extracted from Icelandic seaweed has antibacterial activity.