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 diatoms and one genus with two species of dinoflagellate collected from the surface water of Seto Inland Sea was used for an enrichment culture under bubbling 10% CO2 in air, and a 10% CO2-tolerant microalga was isolated and identified as Thalassiosira weissflogii H1. There was no significant difference between the growth rates and maximum growth yields of this diatom under bubbling 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 total fatty acids in cells under 5-20% CO2 were lower than those under air. However, the ratios of EPA to algal cells-dry weight under 5% CO2, 10% CO2 and 20% CO2 were 0.76, 0.36 and 0.37 (% of dry weight), respectively, as compared with 0.18 under air. There was no significant difference in DHA contents (0.05 under air, 0.13 under 5% CO2, 0.05 under 10% CO2 and 0.09 under 20% CO2), with or without bubbling CO2. The polysaccharide content in the cells under 10% CO2 was higher than that in the cells under air. This study is the first report on a highly CO2-tolerant diatom.