New mechanistic insights into microalgae biofuel production and tetracycline removal under temperature stress

Abstract Industrial production brings high carbon emissions and wastewater pollution, so there is an urgent need to seek new clean energy and low-carbon pollutant treatment methods to contribute to carbon neutrality. In this study, the microalgae growth, lipid production and TC removal efficiency under different temperatures (15, 25 and 35 °C) were investigated. In addition, the molecular mechanisms of lipid accumulation and carbon metabolism were analyzed, and the TC degradation products and pathways were revealed. The results showed that microalgae achieved the highest lipid content (71.25%) under 15°C-TC treatment. Efficient removal of TC was achieved at different temperatures, with the lowest removal rate reaching 90.79% (15 °C). The highest content of reactive oxygen species (569.51 DCF-fluorescence intensity (1 × 10 6 cells) −1 ) and glutathione (52.36 nmol fresh alga −1 ) accumulation was also obtained under 15°C-TC treatment. Metabolic and transcriptomic results indicated that temperature was the key reason for the differences in metabolites and genes, and high genes expression related to lipid synthesis was promoted at 15°C-TC. In addition, microalgae increased the cell resistance by accumulating more amino butyric acid under 15°C-TC. Central carbon metabolism and carbon flow direction indicated that microalgae tended to accumulate more lipids under 15 °C. The degradation of TC was mainly carried out through a number of reactions including dehydration, demethylation, ring opening and dehydroxylation. This study elucidated the effects of TC under different temperatures on the cell growth and lipid accumulation, revealed the biodegradation pathways of TC, and accelerated the process of energy production and green sustainable bioremediation by microalgae.