Morphological and molecular characterization of Apatococcus echinosporus sp. nov . (Trebouxiophyceae, Chlorophyta) isolated from rainwater

This study describes a new species, Apatococcus echinosporus sp. nov. isolated from rainwater collected as atmospheric wet deposition. Apatococcus echinosporus was characterized by spherical vegetative cells with thick cell walls and shallowly lobed, parietal chloroplasts lacking pyrenoids, distinguishing it from other Apatococcus species. Autospores were covered with numerous blunt spines distributed over approximately half of the spore surface. Molecular phylogenetic analyses combined with DNA-based species delimitation analyses revealed that A. echinosporus forms a well-supported clade with isolates collected from the surface of a polyethylene waste container and house dust. The occurrence of this species across diverse environments is consistent with the capacity of aerophytic microalgae to undergo atmospheric dispersal via wet deposition. This finding provides observational support for the role of rainwater in the colonization of terrestrial surfaces by aero-terrestrial algae.