Abstract

A micro-algae strain was isolated from fresh tropical water in Hainan, China. By phylogenetic analysis with 18S rDNA, we identified it as Micractinium pusillumstrain Y-002. To study the relationships between nutrient and lipid accumulation of this strain, we cultured the organism either in complete TAP, SE, BG11 or HSM medium, or media deficient of nitrogen and iron, respectively. HSM media deficient in sulfur, phosphorus (P), magnesium (Mg), potassium (K) or calcium (Ca) were also tested. We found that HSM media, N and S starvation led to significant increase in cellular lipid content; and starvation of Ca and K only resulted in moderate increase of lipid content. Under the HSM-N or HSM-S culture condition, the increase in lipid content was accompanied by marked decrease in photosynthesis efficiency, total protein, and total carbohydrate content. Our investigation of the effect of exogenous carbon on lipid accumulation and photosynthetic efficiency revealed that the cell growth rate, photosynthesis efficiency, and lipid content per volume unit peaked in the presence of 15 mM sodium acetate (NaAC) and higher concentrations of NaAC led to decrease in these physiological traits.

Key words: Micractinium pusillum, lipid content, photosynthetic efficiency, growth rate, biodiesel.