A new genus of soil green microalgae Edaphochloris gen. nov. (Chlorellaceae, Trebouxiophyceae)

Abstract

The problem of studying the species diversity of small single-celled green coccoid microalgae (Chlorophyta) is still relevant, since their simple and uniform cellular morphology makes it extremely difficult to correctly identify them. It is now generally accepted that the best approach for creating a new, more natural classification of “little green balls” is an approach that combines morphological, ecological, physiological and molecular phylogenetic methods. Strains ACSSI 104 and ACSSI 144 were isolated from solonetz and chestnut soil (Volgograd region, Russia). Their cells have a typical Nannochloris-like morphology: single spherical or subspherical cells, chloroplast single, parietal, cup-shaped, without pyrenoid, but with starch grains in it. Old cells accumulate numerous oil droplets in cytoplasm. Reproduction by 2−4 autospores. Autospores of both strains are equal size and exhibit liberation by rupture of sporangium cell wall. Zoospores and sexual reproduction not observed. Both strains are part of independent cluster closely related to genera Marvania, Pumiliosphaera, Nannochloris and Gloeotila. A comparative analysis of morphological (cell size, chloroplast type) and ultrastructural characteristics (structure of cell wall and lamellar system), features of reproduction (asexual reproduction by autospores only) and habitat (soil) with other members of the Nannochloris-clade, as well as results of analysis of 18S rRNA gene and ITS2 secondary structure of the studied strains, allowed us to propose a new genus – Edaphochloris with the type species – E. andreyevae. The report was prepared based on the materials of the V All-Russian Scientific Conference with international participation "Algae: problems of systematics, ecology and use in monitoring", 2021.