A highly CO2-tolerant diatom, Thalassiosira weissflogii H1, enriched from coastal sea, and its fatty acid composition

A marine plankton-net sample containing 18 genera with 26 species of diatom s and one genus with two species of dinoflagellate collected from the surfa ce water of Seto Inland Sea was used for an enrichment culture under bubbli ng 10% CO2 in air, and a 10% CO2-tolerant microalga was isolated and identi fied as Thalassiosira weissflogii H1. There was no significant difference b etween the growth rates and maximum growth yields of this diatom under bubb ling air, 5% CO2 and 10% CO2, but the growth rate and maximum growth yield under 20% CO2 markedly decreased. The percentages of EPA and DHA for the to tal fatty acids in cells under 5-20% CO2 were lower than those under air. H owever, the ratios of EPA to algal cells-dry weight under 5% CO2, 10% CO2 a nd 20% CO2 were 0.76, 0.36 and 0.37 (% of dry weight), respectively, as com pared with 0.18 under air. There was no significant difference in DHA conte nts (0.05 under air, 0.13 under 5% CO2, 0.05 under 10% CO2 and 0.09 under 2 0% CO2), with or without bubbling CO2. The polysaccharide content in the ce lls under 10% CO2 was higher than that in the cells under air. This study i s the first report on a highly CO2-tolerant diatom.