Micractinium lacustre and M. thermotolerans spp. nov. (Trebouxiophyceae, Chlorophyta): Taxonomy, temperature-dependent growth, photosynthetic characteristics and fatty acid composition

The problem of studying the species diversity of representatives of the genus Micractinium (Chlorophyta) remains relevant for its simple morphology and high phenotypic plasticity. At the same time, such studies are of great practical importance, since some of them have high biotechnological potential, because they are capable of accumulating valuable metabolites, including polyunsaturated fatty acids. The studied strains ACSSI 343, ACSSI 344, and ACSSI 345 were isolated from eutrophic reservoirs of the Vasilievsky Lakes system (Samara region, Russia), the strain ACSSI 332 - from a hot spring on the Chukotka Peninsula (Russia). All of them have a Chlorella-like morphology: single spherical cells, without bristles, chloroplast parietal with one pyrenoid, and reproduction by autospores. However, analysis of the fragment 18S-ITS1-5.8S-ITS2 showed that the studied strains belong to the genus Micractinium. Comparison of morphological characteristics at standard temperatures (20-24 degrees C), habitat and lifestyle, phylogenetic analysis findings, results of studying the effects of elevated temperatures (up to 41 degrees C) and the effect of high nutrient content on strain morphology and reproduction, as well as analysis of fatty acids profile allowed to establish that the studied strains are representatives of 2 new species with high biotechnological potential - M. lacustre and M. thermotolerans spp. nov.