This report describes the isolation and culture of Sphaerosorus coelastroides from the plankton of a freshwater river in the central Appalachian mountain chain. This alga was first observed in a dry freshwater riverbed in Central Europe in 1908 and, since then, has been included in Xanthophyceae surveys from nearly all continents with temperate climates. Differential interference microscopic analysis of our isolate revealed cell sizes ranging from 10.2 to 19 μm in diameter occurring in groups of two to 32 cells with a mucilage layer that changed thickness depending upon the phase of the life cycle. Chloroplasts were light green, and confocal fluorescence microscopy revealed three or more per cell. Genetic markers were sequenced, annotated, and deposited into GenBank, and include the 18S nuclear rRNA gene (PX102079) and completed chloroplast (PV826133) and mitochondrial (PV826132) genomes. Phylogenetic analyses using 18S and rbcL gene sequences revealed that this isolate was closely related to S. composita, the only other known species from this genus. This isolate was deposited into the UTEX Culture Collection of Algae, making it the only strain of this alga available for phycological study at this time.
Collins et al. (Mon,) studied this question.