Substrate specificities in the chlorophyll catabolism of aquatic protists determined with in vivo phagocytotic assays.

Chlorophylls (Chls) are ubiquitous photosynthetic pigments with inherent potential to generate cytotoxic reactive oxygen species. Therefore, all phototrophs and any phagotrophs that attempt to digest phototrophic cells have presumably developed mechanisms to mitigate this phototoxicity. In aquatic environments, the Chls produced by the dominant producers, microalgae, are catabolized into nonphototoxic pigments, cyclopheophorbide enols (CPEs), either by microalga-feeding protists or autonomously, particularly by those carrying secondary chloroplasts during the dismantling of their chloroplasts.