Effects of nitrogen sources on the growth, contents of total lipids and total hydrocarbons of Botryococcus braunii

Two microalgae strains, Botryococcus braunii 764 and Botryococcu braunii 765, were chosen for studying the effects of different nitrogen sources and concentrations on the growth, total lipids and total hydrocarbon of energy microalgae in laboratory. Four nitrogen sources, ie. nitrate, nitrite, ammonium and urea, and six concentrations of 0.5, 1, 2, 4, 8 and 10 mmol N/L for each source were applied. The results showed that all four nitrogen sources could be utilized by both B. braunii 764 and B. braunii 765 for their growth, which, however, varied significantly with nitrogen sources, nitrogen concentrations and microalgae strains. Nitrate was the optimal nitrogen source for the growth of both microalgae strains. The optical density, biomass, total lipids and total hydrocarbon of B. braunii 764 with nitrate were 1.38, 1.81 g/L, 27.61% and 34.21% (of its cell dry weight), respectively, which were significantly higher than that of other three nitrogen sources, while for B. braunii 765 the biomass and total hydrocarbon with nitrate were also higher than that of other nitrogen treatments, being 2.15 g/L and 27.89%, respectively, with the exception of the optical density that was the highest with urea (1.87). In comparison with B. braunii 765, the growth rate of B. braunii 764 was a little slow, but its total lipids and total hydrocarbon were higher than that of B. braunii 765, being 27.61% and 34.21%, respectively, compared with 15.75% and 27.89% for B. braunii 765. Significant hormesitic effects with nitrogen concentrations were also observed for both microalgae strains. At the concentration of 2.0 mmol N/L nitrate both the total lipids and total hydrocarbon of B. braunii 764 were the highest, 27.61% and 34.21%, respectively, while B. braunii 765 reached its highest total lipids of 15.75% at the concentration of 4.0 mmol N/L nitrite, and total hydrocarbon of 27.89% at the concentration of 8.0 mmol N/L nitrate. Our findings indicated that overall B. braunii 76be considered as an energy alga candidate for the further exploitation and utilization of its potential.