Physiological response and resistance mechanism of oleaginous microalgae Auxenochlorella protothecoides UTEX 2341 under cadmium treatment

Abstract:

[Background] The problem of heavy metal cadmium (Cd) pollution is becoming increasingly serious. Microalgae is a good biological adsorbent of heavy metals. However, current researches have mainly focused on the Cd removal rate and adsorption performance of microalgae, while their anti-Cd mechanisms were seldom studied. [Objective] In our study, the effects of Cd stress on the physiological character, resistance mechanism and oil productivity of oleaginous microalgae Auxenochlorella protothecoides UTEX 2341 were studied. [Methods] The growth and oil productivity of microalgae under 0?5 mmol/L Cd stress were measured. Changes in pigment, soluble protein and oil content of algae under 2 mmol/L Cd stress were further analyzed, as well as changes in their submicrostructure, antioxidant enzymes, antioxidants and fatty acid components. [Results] Auxenochlorella protothecoides UTEX 2341 could withstand 2 mmol/L of Cd stress. Its biomass and chlorophyll content slightly decreased, while its lipid yield significantly increased to 1.60 g/L at 168 h, 1.77 times of the control. Besides, high Cd treatment induced the accumulation of reactive oxygen species (ROS). In response to the oxidative damage caused by high Cd stress, the microalgae cells initiated their resistance mechanism, as the content of antioxidants of carotenoid and reduced glutathione (GSH) remarkably increased to 1.42 and 4.5 times of the control, alleviating the toxicity of Cd, though the activity of antioxidant enzymes was suppressed by Cd stress. According to the results of fatty acid composition analysis, the content of C18:1 increased and the percentage of C16?C18 reached 96%?98%, meeting the production standard of biodiesel. [Conclusion] This research laid a foundation for future researches on the anti-Cd mechanism of microalgae and the algae lipid synthesis regulation mechanism under Cd stress.