Regulation mechanism of Chlamydomanas reinhardtii responding to different waste nitrogen sources based on transcriptomics

Treatment of nitrogenous flue gas or wastewater using microalgae caters to the strategic goal of sustainable development and environmental protection. However, the physiological responses and metabolic mechanisms of microalgae responding to nitrogenous compounds in flue gas or wastewater are still not well understood. In this study, different nitrogen sources, nitrate, nitrite, and ammonium, were set up to simulate the nitrogen type in nitrogen-containing flue gas or wastewater for cultivation of Chlamydomonas reinhardtii, and the physiological responses and metabolic mechanisms of C. reinhardtii responding to the different types of nitrogen sources were analyzed by biochemical techniques and transcriptome sequencing technology at the RNA level. It was shown that different nitrogen sources can increase biomass production and protein content of C. reinhardtii, but higher concentration of nitrogenous compounds can inhibit growth. The maximum protein content reached 569.05 mg g⁻¹ in N− TAP medium supplemented with 14 mM ammonium nitrogen and the transcriptome results showed that ammonium greatly enhanced the metabolic pathways of N metabolism and C metabolism, indicating that proper concentration of ammonium could be the most direct and readily available nitrogen source for C. reinhardtii. This study lays a theoretical foundation for microalgae to effectively utilize nitrogen sources in nitrogen-containing flue gas or nitrogen-containing wastewater.