Morphology and phylogenetic relationships of two new Antarctic species in phylogroup Chloromonadinia (Volvocales, Chlorophyceae)

The phylogroup Chloromonadinia (Volvocales, Chlorophyceae) comprises green microalgae that inhabit a variety of environments, including freshwater, soil, and snow. Two strains were isolated from two sites in the South Shetland Islands in maritime Antarctica, and their morphological and molecular characteristics were studied. Light microscopy of the strain KSF0090 revealed ellipsoidal or broad ellipsoidal, sometimes almost spherical cells with a chloroplast without a pyrenoid, a prominent eyespot, and a hemispherical papilla. The vegetative cells of KSF0208 were ellipsoidal to ovoid cells with a chloroplast with a central pyrenoid, a linear eyespot, and a papilla. The two strains differed from other closely related species based on size and the aforementioned morphological characteristics. Nuclear small subunit rDNA sequence data indicated that each strain formed a distinct well-supported lineage within the phylogroup Chloromonadinia. In addition, comparative analyses of the secondary structures of internal transcribed spacer 2 and compensatory base changes were used to identify and characterize the two strains. Based on their morphological and molecular characteristics, we propose KSF0090 and KSF0208 as two new species, Chloromonas deceptionensis sp. nov. and Ostravamonas greenwichensis sp. nov., respectively.