Characterization of the Lipid Accumulation in a New Microalgal Species, Pseudochoricystis ellipsoidea (Trebouxiophyceae)

The use of fast-growing oleaginous algal strains is indispensable to achieve low-cost production system for microalgal biodiesel. We therefore previously isolated a new algal species within new genus "Pseudochoricystisas" (invalid name, class Trebouxiophyceae), "Pseudochoricystis ellipsoidea" (MBIC11204), which possesses oil vesicles stainable with a selective fluorescent dye for intracellular lipid droplets, Nile Red (Sekiguchi et al., 12th Annu. Meet. Jpn. Microbiol. Cult. Coll. 2005). In the present study we attempted to investigate growth and lipid accumulation of this new isolate. The maximum growth rate of P. ellipsoidea was 3.46 g dry weight l-1 day-1. Nile Red fluorescence reached maximum intensity within 5-10 days after transferring P. ellipsoidea cells to nitrogen starvation conditions in the light, but not in the dark. Total lipid content made up 32% of normal-grown (+N) and 26% of nitrogen-starved (-N, 8 days) dry weight algal cells, and the hydrocarbon fraction was more than 10 times higher in -N cells. Fatty acid composition changes and an increase in triglycerides to 82% of total lipid were also observed with nitrogen starvation. These results suggest that P. ellipsoidea is a fast-growing oleaginous algal strain in which hydrocarbons and triglycerides can be produced photoautotrophically up to 30% of the dried biomass.