<i>Paulinella acadia</i> sp. nov., a New Photosynthetic Species Isolated From a Brackish Beach in British Columbia (Canada)

Plastids in almost all photosynthetic lineages originated from a primary endosymbiosis between cyanobacteria and heterotrophic eukaryotes in an ancestor of Archaeplastida. Strikingly, this event was repeated about a billion years later in an ancestor of photosynthetic Paulinella. Due to the recent and independent occurrence of this second primary endosymbiosis, Paulinella amoebae serve as a remarkable model group for studying the origin of plastids. To date, three species of photosynthetic Paulinella have been described mainly from freshwater and marine environments. Here, we describe a fourth photosynthetic Paulinella species from a brackish beach near Vancouver (British Columbia, Canada) using morphological and molecular data that we named Paulinella acadia sp. nov. Although P. acadia sp. nov. appears similar to P. chromatophora under light microscopy, scanning electron microscopy and molecular phylogenetic analyses demonstrate its close relationship to P. longichromatophora. The discovery of P. acadia sp. nov. expands the diversity and ecological range within this group. Notably, it is the second photosynthetic Paulinella species found on a beach to be described, alongside its sister P. longichromatophora.