Zeaxanthin

Tocopherols and polyphenols standards, as well as all HPLC grade solvents, were purchased from Sigma–Aldrich (Milano, Italy). Carotenoid standards (violaxanthin, lutein, zeaxanthin, β-cryptoxanthin, and β-carotene) were purchased from Cayman chemicals (Ann Arbor, MI, USA); antheraxanthin was tentatively identified by comparison with retention times and literature UV spectra and quantified by means of lutein standard. Chlorophylls in acetone were purchased from DHI Water & Environment (Copenhagen, Denmark)

Violacein and deoxyviolacein were purchased from AG Scientific. Lycopene, β‐carotene, canthaxanthin, and astaxanthin were purchased from Merck, and zeaxanthin was purchased from Cayman. All strains used in this study are listed in Table S1, Supporting Information. E. coli DH5α (Invitrogen) was used for routine gene cloning works. The previously constructed WLGB‐RPP strain was used as the host strain for carotenoids production,^[29] and the previously constructed IND5 (pTacGEL) was used as the host strain for the production of violacein derivatives.^[14]Chromobacterium violaceum was provided from Korean Collection for Type Cultures (KCTC), which was used to extract the violacein BGC.

A stock solution of zeaxanthin (Cayman Chemical Company, Ann Arbor, MI, USA) was prepared in dimethyl sulfoxide. After acclimation under nonstressful conditions (24°C, 50 μmol photons m⁻² s⁻¹) for 5 days, the Abx algal culture was exposed to either thermal stress (31.5°C, 50 μmol photons m⁻² s⁻¹) for 6 days or light stress (24°C, 200 μmol photons m⁻² s⁻¹) for 1 day to induce oxidative damage. Subsequently, the Abx algal culture was supplemented with zeaxanthin to a final concentration of 0.1 or 1 μg/ml and incubated for 2 days under the same stressful conditions followed by F_v/F_m and ROS production measurements as described above.