Rapid Accumulation of Astaxanthin in Haematococcus pluvialis Induced by Mild Hydrostatic Pressure

Rapid Induction of Astaxanthin in Haematococcus lacustris by Mild Electric Stimulation

“…The inoculum concentration was approximately 0.2 g/L based on dry cell weight (DCW) measurements (see Section 2.6 for details). The bc-PBR was continuously supplied with a gas mixture of 5.0% (v/v) CO 2 and air at a flow rate of 200 mL/min from the bottom of the reactor using a mass flow control system [18]. The bc-PBR was illuminated with a light intensity of 200 ± 10 µmol photon/m 2 /s using three LED lamps positioned in front of the bc-PBR.…”

“…Therefore, to avoid artificial changes in cell color, algal cells were observed under a light microscope immediately after sampling. Cell viability (%) after electrochemical treatment was evaluated using an improved Neubauer hemocytometer (Marienfeld, Lauda-Königshofen, Germany) after staining with trypan blue dye (Sigma Aldrich, St. Louis, MO, USA), which can penetrate the cytoplasmic membranes of damaged microalgal cells [18,30,31]. The comprehensive staining protocol is provided in Supplementary File S2.…”

“…Following electrotreatment, H. lacustris cells were collected by centrifugation at 1952× g for 10 min (Combi R515; Hanil Science Co., Gimpo, Republic of Korea), washed twice with distilled water, freeze-dried using a lyophilizer for 48 h (FD8508; IlShinBioBase Co., Daejeon, Republic of Korea), and stored at −22 • C until further analysis. The cellular contents of AXT and other carotenoids (i.e., canthaxanthin, zeaxanthin, and β-carotene) in H. lacustris were analyzed using bead beating-based solvent extraction and subsequent high-performance liquid chromatography (HPLC), according to recently published protocols [16,18]. Approximately 2 mg of lyophilized H. lacustris cells were mixed with 1.0 g of glass beads (1.5 mm diameter; Daihan Scientific, Gangwon, Republic of Korea) and 1 mL of extraction solution (dichloromethane/methanol [1:1, v/v] containing 0.025 M NaOH).…”

“…AXT biosynthesis is linked to a complex defense mechanism that aids microalgal cells in the management of oxidative stress [11]. Various stress-based approaches, including intense light irradiance [12], high salinity [13], nitrogen deficiency [14], elevated temperature [15], phytohormone supplementation [16], mechanical compression [17], and hydrostatic pressurization [18], have been employed to enhance AXT production. However, the development of an environmentally friendly and effective AXT induction strategy remains a substantial challenge in industrial microalgal biotechnology [6].…”

“…To address these challenges, this study aimed to investigate the technical feasibility of mild electrotreatment (30 mA or below) to stimulate AXT accumulation in H. lacustris while maintaining cell stability under photosynthetic culture conditions. To this end, we utilized the greenish-brown palmella cells of H. lacustris containing previously synthesized AXT intermediates [18]. We found that very mild-intensity, short-duration treatment conditions yielded AXT accumulation approaching the maximum reported yields without any associated toxicity.…”