Search

The slow growth and complex life cycle of Haematococcus lacustris pose significant challenges for cost-effective astaxanthin production. This study explores the use of microfluidic collision treatment to stimulate the germination of dormant seed cysts, thereby improving photosynthetic cell growth and astaxanthin productivity in H. lacustris cultivated in well plate and flask cultures. The flow rate (1.0–3.0 mL/min) and the number of T-junction loops (3–30) were optimized in the microfluidic device. Under optimal conditions (a flow rate of 2.0 mL/min with 10 loops), the total cell number density in well plate cultures increased by 44.5% compared to untreated controls, reaching 28.9 ± 2.0 × 104 cells/mL after 72 h. In flask cultures, treated cysts showed a 21% increase in astaxanthin productivity after 30 d, reaching 0.95 mg/L/d, due to higher biomass concentrations, while the astaxanthin content per cell remained constant. However, excessive physical collision stress at higher flow rates and loop numbers resulted in reduced cell viability and cell damage. These findings suggest that carefully controlled cyst mechanostimulation can be an effective and environmentally friendly strategy for Haematococcus biorefining, enabling the production of multiple bioactive products.

Efficient induction of astaxanthin (AXT) biosynthesis remains a considerable challenge for the industrialization of the biorefinement of the microalga Haematococcus lacustris. In this study, we evaluated the technical feasibility of photosynthetic electrotreatment to enhance AXT accumulation in H. lacustris. The AXT content of H. lacustris electrotreated at an optimal current intensity (10 mA for 4 h) was 21.8% to 34.9% higher than that of the untreated control group, depending on the physiological state of the initial palmella cells. The contents of other carotenoids (i.e., canthaxanthin, zeaxanthin, and β-carotene) were also increased by this electrotreatment. However, when H. lacustris cells were exposed to more intense electric treatments, particularly at 20 and 30 mA, cell viability significantly decreased to 84.2% and 65.6%, respectively, with a concurrent reduction in the contents of both AXT and the three other carotenoids compared to those of the control group. The cumulative effect of electric stimulation is likely related to two opposing functions of reactive oxygen species, which facilitate AXT biosynthesis as signaling molecules while also causing cellular damage as oxidizing radicals. Collectively, our findings indicate that when adequately controlled, electric stimulation can be an effective and eco-friendly strategy for inducing targeted carotenoid pigments in photosynthetic microalgae.