Biotechnology and Bioprocess Engineering 2024; 29(6): 1131-1140  
Effect of reduced atmospheric pressures on the morphology and astaxanthin biosynthesis of microalga Haematococcus lacustris
Sangui Kim 1,2 · Rendi Mahadi 1 · Aditya Lakshmi Narasimhan 1 · Catherine Christabel 1 · Hyoji Yu 1 · Eui-Jin Kim 3 · You-Kwan Oh 1,2
1 School of Chemical Engineering, Pusan National University, Busan 46241, Korea
2 Institute for Environment & Energy, Pusan National University, Busan 46241, Korea
3 Bioresources Research Division, Nakdonggang National Institute of Biological Resources (NNIBR), Sangju 37242, Korea
Correspondence to: ✉ You-Kwan Oh
youkwan@pusan.ac.kr
Received: April 29, 2024; Revised: August 13, 2024; Accepted: August 14, 2024; Published online: September 21, 2024.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
The efficient production of the high-value antioxidant astaxanthin is crucial for economically viable biorefinement of the green microalga Haematococcus lacustris. In this study, we investigated the impact of reduced atmospheric pressure (0.8–0.2 bar) on cell morphology and astaxanthin biosynthesis in H. lacustris over 72 h. Astaxanthin content in microalgal cells subjected to depressurization at an optimal pressure of 0.6 bar for 48 h increased by 26.9 and 13.2% compared with that in initial cells and untreated controls, respectively. Furthermore, depressurization led to increased cell size and elevated levels of canthaxanthin (a major astaxanthin intermediate) and total fatty acids. Depressurized H. lacustris cells maintained high cell viability rates, ranging from 96.0 to 97.5% for 72 h. However, excessive or prolonged pressure reduction, particularly beyond 60 h or at 0.2–0.4 bar, hindered the ability of microalgae to synthesize astaxanthin. Astaxanthin accumulation under reduced pressure is likely associated with the formation of reactive oxygen species, which serve as signaling biomolecules triggering astaxanthin biosynthesis. These findings provide valuable insights into the biology and ketocarotenoid biosynthesis of microalgae under different hydraulic pressure conditions, as well as the responses of other biological components of life support systems required in low-pressure lunar and Martian environments.
Keywords: Haematococcus pluvialis · Astaxanthin · Depressurization · Low-pressure · Reactive oxygen species · Canthaxanthin

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