Current-controlled electrical stimulation regulates growth, redox adaptation, and lipid accumulation in Chlorella vulgaris

Abstract

Microalgae can produce versatile biological products (such as lipids and antioxidants), and environmental stimulation methods are usually employed to enhance the production yield during microalgae cultivation. However, conventional stimulation methods, such as nutrient starvation, inherently offset the overall microalgal biomass yield. To overcome this barrier, this study examined electrochemical stimulation as an efficient and non-invasive strategy by optimally controlling the physiological and redox state of the freshwater microalga Chlorella vulgaris. The mild (0.25 mA) electrochemical stimulation exhibited both enhanced biomass yield (28.1%) and total lipid production (63.1%) compared to the non-stimulated control. Biochemical analyses revealed that the mild electrochemical stimulation triggered a highly coordinated hormetic response, which induced a comprehensive upgrade of the photosynthetic system to meet elevated energy demands while concurrently activating a synchronized antioxidant cascade. By significantly upregulating antioxidant enzyme activities (catalase and peroxidase), Chlorella vulgaris effectively detoxified reactive oxygen species (ROS) and reduced lipid peroxidation by 27.8% on day 8. This efficient redox adaptation mitigated lipid peroxidation, which supported cellular resilience under a controlled electrochemical stimulation, and coincided with enhanced lipid biosynthesis without the energetic burden of severe oxidative repair. In contrast, the intense electrochemical stimulation (0.5 mA) exceeded the cellular antioxidant capacity, limiting the overall enhancement of product yields. This limitation is likely attributed to restricted growth enhancement, as metabolic resources were reallocated to manage oxidative stress. The results indicate that controlled electrochemical stimulation can serve as an effective stress-acclimation approach to cultivate a lipid-enriched and stably redox-adapted algal phenotype.