Enhancing biomass and lipid accumulation in the microalgae Schizochytrium sp. by addition of fulvic acid and EDTA.

Enhancing lipid productivity and reducing oxidative damage is essential for lipid overproduction in microalgae. In this study, addition of 20 mg/L fulvic acid (FA) resulted a 34.4% increase of lipid yield in Schizochytrium sp. Furthermore, the cooperative effect of FA and EDTA on cell growth and lipid production was investigated. The combined addition of 20 mg/L FA and 1.0 g/L EDTA yielded a maximal cell dry weight of 130.7 g/L and lipid productivity of 1.16 g/L/h, representing 36.4% and threefold increase over the non-supplemented group, respectively. Moreover, compared with the non-supplemented group, the combined addition strategy exhibited overall lower levels of reactive oxygen species and malondialdehyde, which accompanied with 66.7% and 81.9% higher superoxide dismutase and catalase activity, respectively. Furthermore, a 24.1-37.1% increase of malic enzyme and 19.4-25.2% decrease of phosphoenolpyruvate carboxylase activity was observed during the entire fermentation stage (0-108 h). Results suggested that the combined addition strategy not only enhanced lipid accumulation, but also prevented the lipid peroxidation.