Establishment of ultrasonic stimulation to enhance growth of Haematococcus lacustris

In this study, ultrasonication at a frequency of 40 kHz was used to shorten the sonication period and enhance the growth of Haematococcus lacustris. To confirm the optimal conditions, the effects of ultrasound output and treatment interval were examined. Under optimal conditions (20 W and 15-day cycle), the maximum cell density and chlorophyll content were 66.75 × 10⁴ cells mL^-1 and 36.54 mg g^-1, respectively, which were increased by 50.00% and 39.01%, respectively, compared to the control. Transmission electron microscopy analysis showed that ultrasonication caused tiny cracks in the W4 and W6 strata but did not disrupt the inner W2 layer. Additionally, RT-qPCR analysis showed that ultrasonication upregulated both cell division and nitrogen uptake. No difference were detected in the composition or quantity of fatty acids. This study demonstrates a novel ultrasonic approach for enhancing the growth of H. lacustris.