Effects of gradual and sudden changes of salinity and light supply for astaxanthin production in Haematococcus pluvialis (Chlorophyceae) Murat Telli 1, * and Günce Şahin 1 With 1 figure Abstract: Astaxanthin, a carotenoid naturally synthesized by Haematococcus pluvialis, is economically important for the nutraceutical, pharmaceutical and food industries due to its high antioxidant and anti-inflammatory proper- ties. We investigated astaxanthin accumulation in H. pluvialis after stepwise versus suddenly increased light supply and salt (NaCl) concentrations. Light was increased from 75 to 150, and then to the final intensity of 350 µmol photons m – 2 s –1 in three-day intervals. The effect of gradually increased salt concentration was examined with two steps from 0.2 to the final concentration of 0.8 % (w/v) in three-day intervals. The overall induction period for astaxanthin accumulation was 13 days. Out of all treatments, stepwise increased light supply resulted in highest cell viability and highest astaxanthin accumulation with 15.76 ± 0.88 mg g –1 dry mass. It is an energy-saving, appropri- ate strategy to achieve optimal astaxanthin accumulation. It moreover resulted in the least biomass loss, which is caused by the provided stress conditions. Keywords: Astaxanthin; Haematococcus pluvialis; stepwise induction; irradiance; sodium chloride; sudden in- crease; cultivation Introduction Astaxanthin ((3S-3’S)-dihydroxy-β,β,-carotene- 4,4’- dione) is a xanthophyll and naturally synthesized by some plants, algae, fungi, and bacteria (Boussiba & Vonshak 1991; Johnson & An 1991). Astaxanthin is economically important for nutraceutical, pharmaceu- tical and food industries due to its high antioxidant, anti-inflammatory and antitumor properties (Kob- ayashi et al. 1997a; Higuera-Ciapara et al. 2006; Hus- sein et al. 2006). It is also used for the pigmentation of many commercially reared aquatic animals, such as the salmonids, shrimp, lobster and crayfish that cannot synthesize this pigment de novo (Lorenz & Cysewski 2000). Haematococcus pluvialis Flotow 1844 (Chla- mydomonadales, Chlorophyceae) is a freshwater green microalga, and known as the organism with highest capability of natural astaxanthin biosynthesis (up to 4 % of dry mass) for industrial applications (Li et al. 2011). H. pluvialis has four cell morphologies (macrozoo- ids, microzooids, palmella, and hematocysts/aplano- spores) between green vegetative motile and red non- motile encysted life stages depending on changes in environmental conditions (Elliot 1934). Under favora- ble conditions, cells are predominantly in the green vegetative stage with high growth rates; the motile macrozooids have two flagella. Under unfavorable conditions induced by environmental stressors, mac- rozooids lose their flagella and increase in volume, accompanied by the termination of cell division and development of resistant, thick cell walls (Kobayashi et al. 1997b; Boussiba 2000). Cells are then developing into non-motile palmella cells and enter the vegeta- Authors’ address: 1 Bolu Abant Izzet Baysal University, Faculty of Art and Science, Department of Biology, 14280 Bolu, Turkey * Corresponding author: tellim@ibu.edu.tr E © 2020 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/fal/2020/1300 1863 - 9135/20/1300 $ 1.75 Fundam. Appl. Limnol. 194/1 (2020), 11–17 Article published online 31 July 2020, published in print August 2020