Enhancing the production of a marine diatom (Skeletonema costatum) with low-frequency ultrasonic irradiation

Abstract

This study evaluated the growth stimulatory effect of low-frequency ultrasound on an ecologically and economically important marine diatom, Skeletonema costatum. To investigate the effect of repeated ultrasonication and the optimum duration of ultrasonication, S. costatum cells were exposed to low-frequency ultrasound (40 kHz) for 0, 2, 30 or 90 s under two sonication conditions: a one-time sonication treatment or a 24-h interval treatment. The cell density and cellular carbohydrate content increased in the ultrasonicated cultures. Similarly, the photosynthetic efficiency, particularly in the exponential growth phase, was enhanced in ultrasonicated cultures, which might account for the enhanced cell growth. At the end of the experiment, compared with the corresponding one-time treatment groups, the cell density in the 30-s sonicated culture and the cellular carbohydrate concentration in the 2-s sonicated culture of the 24-h interval treatment group were increased by 34 ± 4% and 28 ± 3%, respectively. This indicates that, under the same ultrasonic treatment conditions, a higher cellular carbohydrate content can be achieved by repeating the ultrasonication. This study also revealed that, compared with control, the silica/nitrate ratio and silica/phosphate ratio required to produce the same number of S. costatum cells were lower in the sonicated cultures, particularly in the one-time sonicated cultures. This finding indicates that ultrasonic irradiation results in the light silicification of S. costatum cells. This study provides valuable information on the diatom response to low-frequency ultrasonic irradiation and is an important benchmark study for future biotechnological applications of the mass production of S. costatum and other microalgae.