Abstract: The present work was oriented toward analyzing the growth and total lipid accumulation of two green microalgae, Pseudochlorococcum polymorphumUTEX 1791 and PseudochlorococcumtypicumUTEX 1792, both of which were cultured in the BG-11medium but under different sodium nitrate concentrations of 0.3, 0.5, 1.0, and 1.5 g·L^-1. The results showed that the sodium nitrate concentration, ranging from 0.3 to 1.0g·L^-1 was suitable for the growth of P. polymorphumUTEX 1791: its final dry biomass weight was about 3.7g·L^-1. The optimum concentration of sodium nitrate for P.typicumUTEX 1792 was 1.0 g·L^-1, and its final dry biomass weight reached 4.35g·L^-1. The close relationship between the variation of chlorophyll a content and the accumulation of total lipid was observed from these two algal cultures. At the early growth phase, the content of chlorophyll ain all experimental groups increased sharply, while the total lipid accumulation was not significant. However, in the mid growth phase, the content of chlorophyll aincreased slowly, but the total lipid content increased significantly in all experimental groups, especially in the 0.3g·L^-1 of sodium nitrate group, whose total lipid content increased by 11.65% (UTEX1791) and 24.99% (UTEX 1792), the maximum total lipid content and yield were up to 26.28% (dry weight)(UTEX1791) and 44.35% (dry weight) (UTEX 1792), 0.98 g·L^-1 (UTEX 1791) and 1.61 g·L^-1 (UTEX 1792), respectively.

Key words: Pseudochlorococcum polymorphum, Pseudochlorococcum typicum, sodium nitrate, total lipid content, maximum lipid yield