The genus Klebsormidium is a cosmopolitan filamentous alga that belongs to the phylum Charophyta and inhabits a wide range of environments, primarily freshwater, soil, and aerial habitats. Its basal position on the Streptophyta phylogenetic tree, widespread distribution and significant functional role make the genus Klebsormidium an important object for phycological research. To advance the molecular phylogeny of Klebsormidium, we conducted the first comparative evaluation of six species delimitation methods – ASAP (Assemble Species by Automatic Partitioning), LocMin (Local Minima), KoT (K over Theta), GMYC (Generalized mixed Yule-coalescent), mlPTP (Poisson Tree Process with Maximum Likelihood), and bPTP (Poisson Tree Process with Bayesian inference) – using rbcL and concatenated ITS2–rbcL fragments. The accuracy of these methods was further validated against molecular, morphological, and ecological data. According to an integrative approach, Klebsormidium mirabile sp. nov. was proposed as a new charophyte species from soil of the Fergana Valley, Uzbekistan. In addition, a study on the fatty acid composition showed that the authentic strain VKM Al-436 of this new species of Klebsormidium is a potential source of polyunsaturated fatty acids, including linoleic, α-linolenic, and hexadecatrienoic acids.

In recent years, amid an increasing shortage of resources, there has been a steady trend towards the search for new biotechnologically valuable algae strains. This paper presents the results of a study of the taxonomic position, growth characteristics and analysis of the fatty acid profile of two strains of eustigmatophyte microalgae of the genus Vischeria (Heterokontophyta) isolated from the Nadymsky district of the Yamalo-Nenets autonomous okrug (Russia) in order to clarify their biotechnological potential. According to the results of morphological and phylogenetic analysis using internal transcribed spacer 2 (ITS2), the strains were identified as Vischeria sp. In the work, the growth rates of the studied strains were studied in detail, productivity was assessed, the content of total lipids was determined and the fatty acid composition was studied. It has been shown that both strains are active producers of palmitic, eicosapentaenoic and palmitoleic acids. It is noteworthy that, in terms of the content of palmitoleic acid, both strains studied are superior to its traditional sources. In the strains VKM Al-463 and VKM Al-480, the final concentration of palmitic acid was 419.6 ± 18.1 and 501.3 ± 57.0 mg/L; of palmitoleic acid, 896.5 ± 22.5 and 1312.5 ± 109.0 mg/L; and of eicosapentaenoic acid, 109.0 ± 7.5 and 113.7 ± 8.8 mg/L, respectively. During the comparative analysis, it was found that, although both strains had undoubted biotechnological value, it was the VKM Al-480 strain that most effectively accumulated biomass enriched with these acids. This makes it attractive as an alternative source of raw materials for the production of food and feed additives, cosmetics, and biodiesel.

Despite extensive research into green microalgae belonging to the genus Chloroidium, their species diversity and biotechnological potential remain poorly characterized. The strain VKM Al-418, the subject of this study, was isolated from the soil of Duvannyi Yar (Russian Federation). The independent species status of this strain is supported by distinct morphological characteristics, robust phylogenetic placement based on the 18S-ITS1-5.8S-ITS2 fragment, and unique features in the secondary structures of both ITS1 and ITS2, including one compensatory base change (CBC) in the highly conserved helix III of ITS2. Additionally, the species delimitation was also confirmed using five independent algorithmic approaches analyzing four different DNA barcodes. The concatenated ITS1-5.8S-ITS2 fragment is more reliable for species discrimination than the individual ITS1 or ITS2 barcodes. Of the species delimitation methods evaluated, ASAP (Assemble Species by Automatic Partitioning) and GMYC (Generalized Mixed Yule Coalescent) performed best in distinguishing Chloroidium species across multiple barcode regions in our analysis. The fatty acid profile of strain VKM Al-418 was analyzed at 9 °C, 22 °C, and 27 °C and exhibited high plasticity in response to temperature, indicative of an adaptive strategy to its harsh environment. Using this integrative taxonomic approach, we describe Chloroidium pseudoellipsoideum sp. nov., a new species with a distinct phylogenetic positioning and promising biotechnological properties.

Despite the long research history on the genus Coelastrella, its species diversity and biotechnological potential have not been fully explored. For the first time, cluster analysis of morphological characteristics was done in the representatives of the said genus. The results obtained have shown that morphological similarity does not necessarily indicate a molecular genetic relationship. It the light of it, the taxonomic status of species can reliably be determined using specific DNA region, such as 18S-ITS1-5.8S-ITS2. The V4 and V9 regions of gene 18S rRNA are relatively conservative fragments which are not suitable for species identification. The ITS2 can be used as a "short barcode". Among the advanced machine methods for delimitation species, the most effective algorithm for distinguishing Coelastrella species was the Generalized Mixed Yule Coalescent (GMYC) method. This paper represented for the first time our comprehensive review of the works devoted to the analysis of the biotechnological potential of representatives of the genus Coelastrella and shows that fatty acid composition of the three main chemogroups within the studied genus differs. In the future, this may form the basis for predicting the composition of the fatty acid profile of new strains, which is important while searching for organisms with specified biotechnological properties. In conclusion, an integrative approach was employed to describe Coelastrella affinis sp. nov., a new species of the genus Coelastrella with high biotechnological potential. Also, a new description of C. thermophila var. astaxanthina comb. nov. was proposed.

For the first time, the cultivated diversity of microalgae in eroded soils in the northern part of the Fergana Valley in Uzbekistan has been studied based on both morphological and molecular genetic analysis. Ten strains of green microalgae (Chlorophyta) and one charophyte strain (Charophyta) were revealed. Only seven strains could be identified at the species level: Chlorella vulgaris, Chromochloris zofingiensis, Deuterostichococcus epilithicus, Pseudomuriella schumacherensis, and Pseudostichococcus monallantoides. Another four strains were identified only at the genus level and require further study: Bracteacoccus sp., Chlorosarcinopsis sp., Klebsormidium sp., and Tetratostichococcus sp. The low species diversity in the microalgae is likely due to both the low fertility of the eroded soils on the slopes, and the limitations of the culture-based approach that only reveals a fraction of the overall microbial diversity. Microalgal colonization of eroded soils in the arid foothill zone can be facilitated by various adaptations, such as small cell size and the production of extracellular polysaccharides, mycosporine-like aminoacids, and secondary carotenoids. The present work may contribute to the further development of highly functional microalgal consortia, which can lead to improvements and sustainable development of low-productivity, arid, and degraded terrestrial ecosystems.

The objective of this study was to analyze the fatty acid composition of five strains from the genera Chlorella, Micractinium, and Meyerella and conduct an initial assessment of their biotechnological potential. It was found that the strain C. vulgaris VKM Al-335 is a good producer of palmitic acid, the Micractinium strains VKM Al-332 and VKM Al-343 are rich in ω-3 fatty acids, whereas the Meyerella strains VKM Al-346 and VKM Al-428 are producers of ω-6 fatty acids. A comparison of the biotechnological potential of algae with that of higher plant leaves (wheat) demonstrates that algal fatty acids exhibit greater diversity, although it is inferior to wheat leaves in terms of polyunsaturated and ω-3 fatty acids. Correlation analysis showed that when only straight-chain fatty acids were considered, the strains were distributed on the principal component analysis plot in accordance with their genetic relationships. However, when the entire fatty acid profile, inclusive of minor branched-chain and cyclic fatty acids, was analyzed, the algae distribution was in accordance with the environmental conditions in the original habitat, suggesting a possible connection between branched-chain and cyclic fatty acids and microalgae adaptability to environmental temperature conditions.

The present study reports a new representative of Chlorella-clade that was newly isolated from the Lake Vos'merka (Samara region, Russian Federation). 18S-ITS1-5.8S-ITS2 sequence analyses indicated that the studied strain ACSSI 368 and related Chlorella chlorelloides, Chlorella pulchelloides, formed an separate cluster in the Chlorella-clade, unrelated to the holotype of the genus Chlorella - Chlorella vulgaris. The independent place of the genus was also confirmed by genetic distances. The individual species status of the studied strain ACSSI 368, compared with the sister C. chlorelloides, was confirmed by morphological differences (cell number per colony, type of chloroplast, number of autospores), genetic distances of the interspecific level by 18S-ITS1-5.8S-ITS2 fragment, alone by internal transcribed spacer 1 (ITS1) and internal transcribed spacer 2 (ITS2) sequences, one complementary base change in ITS1, and the results of species delimitation using five methods. A description of studied strain ACSSI 368 was provided as an authentic strain of the type species Aliichlorella ignota. Currently, the new genus Aliichlorella also includes Aliichlorella chlorelloides comb. nov. and Aliichlorella pulchelloides comb. nov. In general, six different delimitation algorithms were used in the present study. The ASAP (i.e. assemble species by automatic partitioning) and LocMin (i.e. 'local minimum' function) algorithms showed synchronous results, but their accuracy with respect to closely related species was somewhat lower. The mlPTP algorithm simultaneously aimed to combine closely related species in one and at the same time divide slightly distinguishing strains within a species into several molecular operational taxonomic units. The bPTP algorithm separated excessively Chlorella-clade representatives into individual species. The generalized mixed Yule coalescent (GMYC) algorithm results were consistent the most with the modern understanding of the Chlorella-clade taxonomy. However, the same method is one of the most time-consuming because, for its implementation, it is necessary to carry out long preparatory work. The KoT results were less accurate than the GMYC results, although this is less time-consuming because it does not require the preliminary construction of ultrametric trees.

Four soil eustigmatophyte algal strains isolated from gray forest soils in Moscow and Tula regions of Russia and deposited in the Algal Collection of Soil Science Institute (ACSSI) were examined by morphological and molecular genetic methods. The strains were assigned to the genus Vischeria on evidence of 18S rRNA gene and ITS2 phylogeny. The strains were morphologically similar to V. magna. However, only one of them, ACSSI 026, clustered with the authentic strain SAG 2554, while the other strains formed a separate independent group. The taxonomy of the genus is problematic because its phylogenetic tree based on the 18S rRNA gene and ITS2 is unresolved, the variable regions V4–V5 and V8–V9 of the 18S rRNA gene are noninformative, and the compensatory base change (CBC) concept fails to work (the concept states that closely related species are distinct if even a single CBC occurs in conserved secondary structure regions of ITS2). The concept of species is presumably possible to develop for Eustigmatophyceae and the genus Vischeria in particular when a greater number of eustigmatophyte algal strains are isolated from various biotopes; plastid genes are used or the total plastid genome is deeply sequenced; and ultrastructural, physiological, and biochemical characteristics are studied in more detail.

Despite many publications about Chlorella-like algae, their reliable and accurate identification is still difficult due to their simplicity and high phenotypic plasticity. The molecular approach has revolutionized our understanding of the diversity of ’small green balls’, and a natural classification of this group is currently being developed. This work is aimed at providing a detailed study of the phylogenetic position, morphology, ultrastructure, and physiology of the biotechnologically remarkable Chlorella-like strain IPPAS C-1210. Based on the SSU–ITS1–5.8S–ITS2 phylogeny, genetic distances, and the presence of compensatory base changes (CBCs) in ITS1 and conserved regions of ITS2 secondary structures, we describe a new genus, Neochlorella, with IPPAS C-1210 as the authentic strain of the type species, N. semenenkoi gen. and sp. nov. In addition, we justify the reassignment of the strain C. thermophila ITBB HTA 1–65 into N. thermophila comb. nov. The distinctive ultrastructural and physiological traits of the new species are discussed.

The taxonomic diversity of the algal genus Meyerella is difficult to study because of its very simple morphology. Within the Chlorella -clade Meyerella members are distinguished from the others by the absence of the pyrenoid. However, it is not possible to identify them only on the basis of light microscopy data without the involvement of molecular genetic analysis methods. Some Meyerella representatives have high biotechnological potential, because they are able to accumulate valuable metabolites, including polyunsaturated fatty acids. As a rule, water bodies are the main habitats for these green microalgae. However, strains ACSSI 428 and ACSSI 429, which described in detail in this study, were isolated from peat cryozems (Sakha Republic, Russia). In this study, a detailed comparative analysis of the morphology, phylogeny and fatty acid profiles of these strains isolated from soil and representatives of other planktonic species, primarily Myerella similis , was carried out. Based on the results obtained, it was found that the studied strains are representatives of a new species with high biotechnological potential – Myerella krienitzii sp. nov.

Biological collections are systematic repositories of living cultures or fixed preparations, they provide researchers with the material required both for basic and applied studies and for educational activities. A collection sample is the only reliable evidence of the existence of a living organism in time and space, whose multifunctionality allows it to be studied as a part of biodiversity and as a bioresource for the development of biotechnologies. Microalgae are an ancient ecological group of taxonomically diverse organisms (cyanobacteria, diatoms, charophytes, green and yellow-green algae, etc.), possessing unique physiology, broad ecological valency and plasticity, which results in their predominance in various habitats. This evolutionally successful group is also in high demand for commercial applications in environmental monitoring, agriculture, bioenergetics, pharmacy, and the food industry. The analysis of data from an independent survey of 21 Russian collections of microalgae and cyanobacteria is provided. The survey included information on the main characteristics of the collections (funds, profile, methods, document management, etc.), emerging problems, and approaches to their solution.

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.

In this article, the system of the green microalgal genus Micractinium, based on morphological, physiological, ecological and molecular data, is considered. The main diagnostic species characteristics and the taxonomic placement of some taxa are also discussed. Phylogenetic analysis showed that the genus Micractinium is characterized by high cryptic diversity. The algorithms used for species delimitation had different results on the number of potentially species-level clusters allocated. The ABGD method was less “sensitive”. The tree-based approaches GMYC and PTP showed a more feasible taxonomy of the genus Micractinium, being an effective additional tool for distinguishing species. The clustering obtained by the latter two methods is in good congruence with morphological (cell size and shape, ability to form colonies, production of bristles, chloroplast type), physiological (vitamin requirements, reaction to high and low temperatures), molecular (presence of introns, level of genetic differences, presence of CBCs or special features of the secondary structure in ITS1 and ITS2) and ecological characteristics (habitat). The polyphyly of the holotype of the genus M. pusillum as well as M. belenophorum is shown. The intron was effective as an additional tool for distinguishing species, and the results of the intron analysis should be taken into account together with other characteristics. The CBC approach, based on the search for compensatory base changes in conservative ITS2 regions, was successful only for distinguishing cryptic species from “true” members of M. pusillum. Therefore, to distinguish species, it is more effective to take into account all the CBC in ITS1 and ITS2 and analyze characteristic structural differences (molecular signatures) in the secondary structure of internal transcribed spacers. The genetic distances analysis of 18S–ITS1–5.8S–ITS2 nucleotide sequences showed that intraspecific differences in the genus ranged from 0 to 0.5 % and interspecific differences, from 0.6 to 4.7 %. Due to the polyphasic approach, it was possible to characterize 29 clusters and phylogenetic lines at the species level within the genus Micractinium and to make assumptions about the species.

Despite that the diversity of chlorophycean microalgae has been studied for a long time, our knowledge of their taxonomic and phylogenetic relationships is still deficient. This study represents one of the first efforts to examine the congruence of the morphological identification of microalgal species from genera Eubrownia, Spongiococcum, and Chlorococcum with DNA-based species delimitation methods. We found unique combinations of morphological, molecular, and ecological features, distinguishing some members of the Moewusinia clade at the genus and species levels. Most genetic groups recovered by GMYC, ABGD, and PTP analyses of 18S rRNA and ITS2 were consistent with their morphological identification. The ITS2 region of genera Eubrownia and Chlorococcum is among the longest within the chlorophytes theretofore studied and has a unique secondary structure with branched helix III and uncommonly long helix IV. Moreover, the molecular signatures were found in the basal stem region of helix I, distinguishing two genera. The CBC analysis is able to effectively discriminate between E. isobilateralis, E. aggregata, and all Chlorococcum species, except for C. infusionum and C. echinozygotum. Thus, we confirmed tentative hypotheses of species, obtained by DNA-based delimitation methods, with morphological data, molecular signatures, ITS2 secondary structure, and CBC criterion.

The correct identification of species diversity of small single-celled green coccoid microalgae still causes difficulties, since their relatively simple morphology hides a high physiological, ecological and genetic diversity. The use of molecular genetic methods has revolutionized the study of the true biodiversity of so-called “small green balls,” allowing the discovery of numerous new taxa. This article presents the results of a study of strains recently isolated from small freshwater urbanized lakes (Vasilievsky Lakes system, Samara region, Russian Federation). Morphologically, these strains were close to the genus Meyerella: spherical cells, cup-shaped, or wide girdle-shaped parietal chloroplast without pyrenoid. Analysis of the 18S–ITS1–5.8S–ITS2 sequences also showed that the studied strains belong to this genus. Comparison of morphological characteristics, habitat and lifestyle, analysis of tree topology, genetic distances and secondary structures of the ITS1 and ITS2 spacers of the Meyerella members, as well as the delimitation results using the Automatic Barcode Gap Discovery (ABGD) method, the Poisson Tree Processes (PTP) model, the Generalized Mixed Yule The Coalescent (GMYC) method allowed us to establish that the studied strains ACSSI 346, ACSSI 362 and ACSSI 363 are representatives of a new species – M. similis sp. nov.

In the present study, Chlorella -like strains of green microalgae from various commercial biological products were studied for the first time using morphological and molecular genetic analyses. It was found that representatives of the Chlorella clade or sister Parachlorella clade were present in all analyzed samples. In addition, microalgae from the genera Edaphochlorella , Chloroidium , Edaphochloris , and Muriella belonging to the Trebouxiophyceae class and Coelastrella and Chromochloris belonging to the Chlorophyceae class were found. According to direct light microscopy data, filamentous cyanobacteria were observed in all preparations, and the presence of diatoms was also noted in the Gera biopreparation. Since the correct identification of green microalgae based on phenotypic traits is very difficult due to their scarcity, lack of information, and variability, the control of the composition of microalgae in biological products should be carried out using modern molecular genetic methods.

— The results of morphological and phylogenetic analysis of Coleochlamys apoda strain ACSSI 377, isolated from the biological soil crust on the surface of a sandy substrate in the North of Russia (Murmansk region) are presented. Morphology is described, including the presence of mature S-shaped cells typical of the species С. oleifera , and formation of synzoospores was reported for the first time for the species. Analysis of the 18S rRNA and rbc L gene sequences indicated that the strain belonged to the species Coleochlamys apoda (order Microthamniales ); this is the first finding of this species found in the Russian territory confirmed by molecular genetic techniques. The presence of clades consisting of uncultured clones on the 18S rRNA gene tree was an indication of the order being insufficiently studied and of the prospects of detection and description of its new members. Ecology and distribution of Coleochlamys and of the sister genus Microthamnion were analyzed based on the literature date and the authors’ observations . Members of the genus Coleochlamys prefer cold habitats and occur within a limited geographic range, in contrast to Microthamnion , which has been repeatedly found in various regions.

SUMMARY Correctly identifying species of Chlorella ‐like microalgae is difficult because of their morphological simplicity and high phenotypic plasticity. The use of molecular tools has revolutionized research on algal diversity, enabling such advances as the discovery of numerous new taxa. This article presents the results of a study of strains that are newly isolated from a freshwater Lake Prudovikov (Samara region, Russian Federation). These strains had the typical Chlorella morphology, exhibiting spherical cells and a cup‐shaped parietal chloroplast. The chloroplast contained a single pyrenoid enveloped by starch grains. However, 18S–ITS1–5.8S–ITS2 sequence analyses indicated that the studied strains are strongly allied with the well‐supported genus Micractinium . Based on the results of a comparative analysis of the morphological, molecular and environmental characteristics of the studied strains (employing a polyphasic approach), we propose that they are new species of Micractinium : Micractinium kostikovii sp. nov.