{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,19]],"date-time":"2026-06-19T12:18:14Z","timestamp":1781871494139,"version":"3.54.5"},"reference-count":35,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T00:00:00Z","timestamp":1774396800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Chiang Mai University\n\t\t\t\t\t\t              https:\/\/ror.org\/05m2fqn25"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Life"],"abstract":"<jats:p>Short-wavelength ultraviolet radiation can impair biological systems by causing DNA damage, oxidative stress, and disruption of photosynthetic processes. Although ultraviolet C (UVC) at 254 nm is widely used as a controlled laboratory stressor, the extent to which trophic condition influences repeated UVC tolerance in phototrophic protists remains unclear. Here, we examined the response of Euglena gracilis grown under photoautotrophic or ethanol-supported mixotrophic conditions and exposed to daily UVC pulses for five days. Cell growth, photosynthetic pigments, intracellular oxidative stress measured by 2\u2032,7\u2032 dichlorodihydrofluorescein diacetate fluorescence, and lipid peroxidation estimated as thiobarbituric acid reactive substances equivalent malondialdehyde were assessed, together with qualitative fluorescence microscopy. Repeated UVC exposure reduced cell density in both trophic conditions, with stronger inhibition under photoautotrophy. Photoautotrophic UVC-treated cultures showed the highest oxidative stress signal, whereas malondialdehyde displayed only a non-significant directional increase. Mixotrophic cultures maintained higher cell density under UVC and showed lower oxidative stress signals than photoautotrophic UVC-treated cultures. Pigment responses also differed between trophic conditions, with increased chlorophyll a and carotenoids per cell under photoautotrophic UVC treatment, while mixotrophic pigment levels remained comparatively stable. These findings show that trophic condition shapes repeated UVC stress responses in E. gracilis and that ethanol-supported mixotrophy is associated with improved physiological robustness under the present experimental conditions.<\/jats:p>","DOI":"10.3390\/life16040539","type":"journal-article","created":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T10:07:13Z","timestamp":1774433233000},"page":"539","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Trophic\u00a0Condition Shapes UVC Responses in Euglena gracilis"],"prefix":"10.3390","volume":"16","author":[{"given":"Sutthiphat","family":"Sriwari","sequence":"first","affiliation":[{"name":"Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kittiya","family":"Phinyo","sequence":"additional","affiliation":[{"name":"Research Group on Space Weather and Cosmic Rays from Ground-Based Observations and Effects on Earth-Space Ecology, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Algal and Cyanobacterial Research Laboratory, Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Office of Research Administration, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sakawwarin","family":"Prommana","sequence":"additional","affiliation":[{"name":"Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7923-4525","authenticated-orcid":false,"given":"Sitthisak","family":"Intarasit","sequence":"additional","affiliation":[{"name":"Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Research Group on Space Weather and Cosmic Rays from Ground-Based Observations and Effects on Earth-Space Ecology, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Center of Excellence in Microbial Diversity and Sustainable Utilization, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0988-4722","authenticated-orcid":false,"given":"Chanenath","family":"Sriaporn","sequence":"additional","affiliation":[{"name":"Research Group on Space Weather and Cosmic Rays from Ground-Based Observations and Effects on Earth-Space Ecology, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Office of Research Administration, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8878-6607","authenticated-orcid":false,"given":"Jeeraporn","family":"Pekkoh","sequence":"additional","affiliation":[{"name":"Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Research Group on Space Weather and Cosmic Rays from Ground-Based Observations and Effects on Earth-Space Ecology, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Algal and Cyanobacterial Research Laboratory, Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sahutchai","family":"Inwongwan","sequence":"additional","affiliation":[{"name":"Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Research Group on Space Weather and Cosmic Rays from Ground-Based Observations and Effects on Earth-Space Ecology, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Algal and Cyanobacterial Research Laboratory, Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"},{"name":"Center of Excellence in Microbial Diversity and Sustainable Utilization, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,25]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1016\/S0094-5765(98)00186-6","article-title":"The Martian and extraterrestrial UV radiation environment\u20141. 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