Kinetic and transcriptional exploration of Chlorella sorokiniana in heterotrophic cultivation for nutrients removal from wastewaters

Abstract Wastewater effluents containing nutrients would lead to eutrophication in natural water bodies, whereas microalgae based treatment could effectively allow their safe disposal. In this study, a green microalga Chlorella sorokiniana , able to grow under both light and lightless conditions, was investigated for its ability to remediate wastewater under heterotrophic conditions. The kinetics of the removal process was modeled and the cellular transcriptional responses in critical metabolic steps were assessed to unravel the nutrients assimilation puzzle. The experimental results demonstrated that C. sorokiniana had substantial tolerance to high nutrients concentrations. Meanwhile, the nutrients removal efficiency and rate were largely influenced by the initial concentration of nutrients. The highest removal efficiency up to 99% was achieved in the culture containing 123.6 mg N L − 1 and 26.8 mg P L − 1 . The decline of nutrients in waters was found following the first-order kinetics. The transcriptional expressions of nrt2 , nr and ppk genes were directly affected by the external concentration of N and P, which indicates the correlation between the nutrients assimilation process by C. sorokiniana and its intracellular metabolic activity rather than the change of biomass quantity. In all, comparing to previous reports, this study validates that heterotrophic cultivation of this microalga is a promising technology for advanced wastewater treatment, with reasonable treatment performance and profound mechanism analysis.