Growth and physiological responses of Isochrysis galbana under varying agitation frequencies

Agitation plays a pivotal role in microalgal cultivation. Insufficient agitation leads to sedimentation and reduced productivity, while excessive agitation causes shear stress and cellular damage, both of which limit microalgal growth. The brown marine haptophyte Isochrysis galbanais widely valued for its rich nutritional profile and diverse bioactive compounds, with applications across aquaculture, nutraceutical, and medical sectors. Despite its potential, optimizing culture conditions remains a challenge, particularly regarding agitation, which is critical for nutrient distribution but often overlooked in terms of frequency. This study investigated the growth performance and physiological responses of Isochrysis galbana (UPMC-A0083) under four agitation frequencies (1/1, 1/10, 1/20, and 1/30 minutes of agitation per minute of operation (moa/moo)). Continuous agitation (1/1 moa/moo) exhibited the highest cell number of 14.99 million cells/mL, biomass of 0.62 g/L, and specific growth rate of 0.58 /day by day 18, significantly (P<0.05) outperforming intermittent agitations. Additionally, the microalga exhibited superior photosynthetic efficiency with Fv/Fm of 0.61, higher nitrate uptake at 99.16%, and smaller cell size of 19.60 μm² under continuous agitation. These findings highlight the critical role of agitation frequency in determining microalgal physiological performance and offer valuable insights for establishing effective strategies to maximize microalgal productivity, thereby enhancing the feasibility of microalgal-based applications.