Two microalgal strains, Chloroidium dehydrum sp. nov. and Chloroidium satellitum sp. nov. (Trebouxiophyceae, Chlorophyta), isolated under high light exposure conditions and exhibiting stress‐induced morphological changes

SUMMARY Exposure of common photosynthetic organisms to intense light, combined with environmental stresses such as drought or high salinity, accelerates the onset of photooxidative stress and inhibits their growth. In this study, we isolated two strains of the eukaryotic microalgae Edo5 and GoA2, which successfully endured rigorous high light exposure screening. To investigate their morphology, we used light microscopy, as well as scanning and transmission electron microscopy, to examine cell surface microstructures and the localization of intracellular organelles. Furthermore, we examined morphological changes under conditions with or without photooxidative stress. Under stress conditions, both strains exhibited cell wall thickening and oil droplet accumulation. Notably, strain Edo5 showed pronounced morphological changes, including the formation of cell walls covered with a distinctive granular structure. Both strains were identified as novel species within the genus Chloroidium , based on morphological characteristics and molecular phylogenetic analyses of the SSU‐ITS1‐5.8S‐ITS2 region and rbc L gene sequences, combined with the detection of compensatory base changes (CBCs) in the ITS2 region. Herein, for these species, we propose the names Chloroidium dehydrum sp. nov. and Chloroidium satellitum sp. nov.