Assessment of the biological invasion risks associated with a massive outdoor cultivation of the green alga, Pseudochoricystis ellipsoidea

Pseudochoricystis ellipsoidea MBIC 11204 is a unicellular green alga that accumulates, under certain stress conditions, lipids consisting primarily of triacylglycerols. The spread of P. ellipsoidea cells from an outdoor raceway pond into the surrounding area was investigated over 35 days by detecting the psbA gene of this alga in water-containing vessels installed at variable distances (between 0 and 150 m) from the raceway pond. psbA was detected even in vessels placed 150 m apart, demonstrating the ability of P. ellipsoidea to spread via wind. Based on this finding, we evaluated the survival and growth of P. ellipsoidea in various environmental water samples. P. ellipsoidea grew well in water containing > 2 mg/L nitrate, but growth was not observed in water containing 3 mg/L of ammonia if the nitrate concentration was < 1 mg/L. The addition of nitrate to produce the final concentration of 3 mg/L improved the growth, demonstrating that nitrate is the growth-limiting nutrient in these water samples.