4338 | wileyonlinelibrary.com/journal/jam J Appl Microbiol. 2022;132:4338–4348. © 2022 Society for Applied Microbiology. INTRODUCTION There is currently great interest in using microalgae for applications in several fields such as nutrition, cosmetic or sustainable chemicals manufacturing, for exam- ple, plastic or pharmaceutical synthesis intermediates (Udayan et al., 2021). Natural carotenoids and polyun- saturated lipids are among the high-value products of commercial interest derived from eukaryotic microalgae biomass (Udayan et al., 2021). For instance, astaxanthin, 3,3′-dihydroxy-4,4′-diketo- β- β carotene is produced, mainly for its antioxidant activities, by the microalga Haematococcus pluvialis (Oslan et al., 2021). Industrial production of carotenoid by the species is typically car- ried out in two stages. In the first step, the microalgae are cultured in optimal growth conditions to produce biomass mainly in photoautotrophic and sometimes mixotrophic regimes (Udayan et al., 2021). The cultures are then sub- jected to conditions of nutritional or environmental stress, to induce accumulation of the carotenoid. The life cycle Received: 28 December 2021 | Revised: 17 March 2022 | Accepted: 21 March 2022 DOI: 10.1111/jam.15540 ORIGINAL ARTICLE Comparative study on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells: UVA light-induced stimulation Meriem Ben Hamouda 1,2,3 | Adnane Kacem 2 | Lotfi Achour 2 | Youssef Krichen 3 | Jack Legrand 1 | Dominique Grizeau 1 | Catherine Dupré 1 1 Oniris, CNRS, GEPEA, UMR 6144, Nantes University, Saint-Nazaire, France 2 Research Laboratory LR14-ES06: Integrative Biology and Bioresources Valorization BIOLIVAL, High Institute of Biotechnology, University of Monastir, Monastir, Tunisia 3 BioAlguesTunisie, Mahdia, Tunisia Correspondence Catherine Dupre, Nantes University, Oniris, CNRS, GEPEA, UMR 6144, Saint-Nazaire F-44600, France. Email: catherine.dupre@univ-nantes.fr Funding information MBH is supported by a grant from Monastir University (alternation scholarship), by the MOBIDOC scheme, funded by the EU through the EMORI program and managed by the ANPR, and by the company BioAlgues Tunisie. Abstract Aim: This study aims to determine how photosynthetic and antioxidant activities vary in vegetative and dormant cells of Haematococcus pluvialis subjected to stresses in conditions representative of industrial productions of microalgae under solar light. Methods and Results: The effects of short-term oxidative treatments were exam- ined on photosynthetic and antioxidant activities of Haematococcus pluvialis vegeta- tive and resting cells. The vegetative cells have 1.6 times higher levels of phenolic compounds, but 1.7 times less catalase, ascorbate peroxidase and superoxide dis- mutase activities than the astaxanthin-enriched resting cells. Mainly, a UVA dose of 4 J cm −2 induced increases in photosystem II electron transport rates (ETRmax) (+15%), phenolic compounds (+15%), astaxanthin (+48%), catalase (+45%) and su- peroxide dismutase (+30%) activities in vegetative cells. Conclusion: The UVA dose strongly stimulates the photosynthetic and antioxidant activities of vegetative cells, but only the accumulation of astaxanthin in resting cells. Significance and Impact of the Study: These preliminary results show that oxida- tive stresses at sub-lethal levels can stimulate the activities of microalgae. Further investigations are needed to estimate the real influence on metabolite productivities in industrial production conditions. KEYWORDS antioxidant activities, astaxanthin, Haematococcus pluvialis, hydrogen peroxide, oxidative stress, phenolic compounds, photosynthetic activities, UVA, UVB Downloaded from https://academic.oup.com/jambio/article/132/6/4338/6988767 by guest on 20 January 2023