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SUMMARY Species of the green algal genus Mychonastes have been recognized as ubiquitous ultrasmall components of freshwater communities worldwide, mainly based on molecular data. However, detailed taxonomic identification of Japanese members of Mychonastes has not yet been conducted. We taxonomically identified species of 13 Mychonastes strains in the Microbial Culture Collection at the National Institute for Environmental Studies originating from Japan based on molecular data and comparative morphology. The strains were classified into 10 species, including four new species, Mychonastes ariiae Nozaki sp. nov. (NIES‐2900), Mychonastes takamurae Nozaki sp. nov. (NIES‐2334, 2336), Mychonastes kasaiae Nozaki sp. nov. (NIES‐3743) and Mychonastes gigas Nozaki sp. nov. (NIES‐2340). Ultrastructural features of the cell walls and chloroplasts of these four species were consistent with the generic concept of Mychonastes. The four new species are distinguishable from other species of Mychonastes based on differences in nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) sequences and morphological features including the mucilaginous matrix surrounding the cells, mode of rupture of the mother cell wall during daughter cell release, formation of large colonies in liquid culture and colony morphology on agar plates. The evolution of Mychonastes species is discussed based on phylogenetic inferences obtained using a combined dataset for four chloroplast genes (psaB, rbcL, psbC and atpB) and rDNA ITS sequences. [ABSTRACT FROM AUTHOR]

A new species of green coccoid algae, Mychonastes hindakii sp. nov., was isolated from the River Moscow (Russia, Moscow). The taxon is described using morphological and molecular methods. Mychonastes hindakii sp. nov. belongs to the group of species of the genus Mychonastes with spherical single cells joined with mucilaginous, irregularly shaped stalks. A comparison of ITS2 rDNA sequences and its secondary structures combined with the compensatory base changes approach confirms the separation between Mychonastes hindakii and other species of the genus. Mychonastes hindakii sp. nov. represents a cryptic species that can only be reliably identified using molecular data. [ABSTRACT FROM AUTHOR]

Abstract Background Picophytoplankton are abundant and can contribute greatly to primary production in eutrophic lakes. Mychonastes species are among the common eukaryotic picophytoplankton in eutrophic lakes. We used third-generation sequencing technology to sequence the whole genome of Mychonastes homosphaera isolated from Lake Chaohu, a eutrophic freshwater lake in China. Result The 24.23 Mbp nuclear genome of M.homosphaera, harboring 6649 protein-coding genes, is more compact than the genomes of the closely related Sphaeropleales species. This genome streamlining may be caused by a reduction in gene family number, intergenic size and introns. The genome sequence of M.homosphaera reveals the strategies adopted by this organism for environmental adaptation in the eutrophic lake. Analysis of cultures and the protein complement highlight the metabolic flexibility of M.homosphaera, the genome of which encodes genes involved in light harvesting, carbohydrate metabolism, and nitrogen and microelement metabolism, many of which form functional gene clusters. Reconstruction of the bioenergetic metabolic pathways of M.homosphaera, such as the lipid, starch and isoprenoid pathways, reveals characteristics that make this species suitable for biofuel production. Conclusion The analysis of the whole genome of M. homosphaera provides insights into the genome streamlining, the high lipid yield, the environmental adaptation and phytoplankton evolution.

A new species of green coccoid algae, Mychonastes hindakii sp. nov., was isolated from the River Moscow (Russia, Moscow). The taxon is described using morphological and molecular methods. Mychonastes hindakii sp. nov. belongs to the group of species of the genus Mychonastes with spherical single cells joined with mucilaginous, irregularly shaped stalks. A comparison of ITS2 rDNA sequences and its secondary structures combined with the compensatory base changes approach confirms the separation between Mychonastes hindakii and other species of the genus. Mychonastes hindakii sp. nov. represents a cryptic species that can only be reliably identified using molecular data.

We investigated how the N:P ratio can shape the structure of picophytoplankton and Microcystis, which are abundant and widespread in eutrophic lakes. Unialgal culture and coculture batch experiments were conducted to study the growth and interspecific competition of Microcystis and two freshwater picophytoplankton species, Mychonastes and Synechococcus, with varying N:P ratios. The results showed that the Ks values of Mychonastes and Synechococcus were more than two times smaller than those of Microcystis, and their μmax values were much higher than those of Microcystis due to their small size. Our results also revealed that the N:P ratio is important for shaping phytoplankton community structure even under high nutrient conditions. The optimal N:P ratios are 64, 32, and 32 for Mychonastes, Microcystis, and Synechococcus, respectively. Thus, Mychonastes outcompeted Microcystis when the N:P ratio was higher than 64, while Microcystis and Synechococcus grew equally well under all of the N:P ratio levels, since they have the same optimal N:P ratio.

Background: Picophytoplankton are abundant and can contribute greatly to primary production in eutrophic lakes. Mychonastes species are among the common eukaryotic picophytoplankton in eutrophic lakes. We used third-generation sequencing technology to sequence the whole genome of Mychonastes homosphaera isolated from Lake Chaohu, a eutrophic freshwater lake in China. Result: The 24.23 Mbp nuclear genome of M.homosphaera, harboring 6649 protein-coding genes, is more compact than the genomes of the closely related Sphaeropleales species. This genome streamlining may be caused by a reduction in gene family number, intergenic size and introns. The genome sequence of M.homosphaera reveals the strategies adopted by this organism for environmental adaptation in the eutrophic lake. Analysis of cultures and the protein complement highlight the metabolic flexibility of M.homosphaera, the genome of which encodes genes involved in light harvesting, carbohydrate metabolism, and nitrogen and microelement metabolism, many of which form functional gene clusters. Reconstruction of the bioenergetic metabolic pathways of M.homosphaera, such as the lipid, starch and isoprenoid pathways, reveals characteristics that make this species suitable for biofuel production. Conclusion: The analysis of the whole genome of M. homosphaera provides insights into the genome streamlining, the high lipid yield, the environmental adaptation and phytoplankton evolution. [ABSTRACT FROM AUTHOR]

We investigated how the N:P ratio can shape the structure of picophytoplankton and Microcystis, which are abundant and widespread in eutrophic lakes. Unialgal culture and coculture batch experiments were conducted to study the growth and interspecific competition of Microcystis and two freshwater picophytoplankton species, Mychonastes and Synechococcus, with varying N:P ratios. The results showed that the Ks values of Mychonastes and Synechococcus were more than two times smaller than those of Microcystis, and their μmax values were much higher than those of Microcystis due to their small size. Our results also revealed that the N:P ratio is important for shaping phytoplankton community structure even under high nutrient conditions. The optimal N:P ratios are 64, 32, and 32 for Mychonastes, Microcystis, and Synechococcus, respectively. Thus, Mychonastes outcompeted Microcystis when the N:P ratio was higher than 64, while Microcystis and Synechococcus grew equally well under all of the N:P ratio levels, since they have the same optimal N:P ratio. [ABSTRACT FROM AUTHOR]

Microalgae have been considered as ideal feedstocks for biodiesel production but the potential application is still under investigations. Here, eight kinds of microalgae were identified from water samples based on the morphologic and phylogenetic analyses. Among these eight microalgae, two Mychonastes S4 and S15 exhibited relative faster growth rate in the early culture stage and the highest contents of lipids. The two Mychonastes also showed higher C18:1 contents than the two Chlorella which were traditionally considered to be potential species for biodiesel production. As one kind of less researched microalgae, this study suggests Mychonastes should be a potential feedstock for biodiesel production. The application of the microalgal biodiesel still have some limiting factors, however, it is promising based on better lipid extraction technology and more relevant studies. [ABSTRACT FROM AUTHOR]

Stentor polymorphus ( Müller) Ehrenberg ( Heterotrichea, Ciliophora) is a trumpet-form ciliate with endosymbiotic green algae (photobionts). Previous reports have indicated that this photobiont has a form typical of Chlorella Beijerinck ( Trebouxiophyceae), with one chloroplast and a distinct pyrenoid. We collected S. polymorphus from an artificial pond on the shore of Lake Biwa in Japan. Microscopic examination demonstrated that there was no pyrenoid in the photobiont, and thus we analyzed the cytological, genetic, and biochemical characteristics of these algal cells. Cultured photobionts were smaller than those in hospite. Phylogenetic analyses placed the photobiont within the genus Mychonastes Simpson and Van Valkenburg, a chlorophycean alga occurring in fresh/brackish waters that lacks pyrenoids. Mychonastes provided little photosynthate to its host; the quantity of carbohydrate amounted to only 2% of that provided to Paramecium bursaria ( Ehrenberg) Focker by its photobiont. [ABSTRACT FROM AUTHOR]

The generic concept of the chlorophycean green algae Mychonastes (preferably living solitary) and Pseudodictyosphaerium (preferably living in colonies) is evaluated by means of small-subunit and internal transcribed spacer (ITS) rRNA gene sequence analyses and microscopical observations. Members of these genera belong to the most common chlorophycean algae of the picoplankton and small-sized nanoplankton of fresh and brackish waters. The morphological difference solitary vs colonial life form is not reflected by molecular phylogenetic data, and it is therefore systematically irrelevant. Consequently, all taxa of the two genera are combined under the generic name Mychonastes. The genus Mychonastes is emended. The synonymy of Mychonastes homosphaera (formerly Chlorella homosphaera) and Chlorella minutissima is confirmed. Eight new species are described from inland waters of Europe, Africa, Asia and South America. Besides certain morphological criteria such as shape and size of the cells and appearance and organization of the mucilaginous strands among the cells of colonies, the main diacritic features are of genetic nature. Comparing the secondary structure of ITS-2, compensatory base changes are found to discriminate the new species. The species of Mychonastes form a monophyletic clade within the Sphaeropleales sensu lato. [ABSTRACT FROM AUTHOR]

Rapid development and drastic population increase in Qatar have led to increasing awareness about food security. Microalgae are considered one of the most promising feedstocks owing to their ability to produce nutrients, including lipids, carbohydrates, and proteins, in addition to antioxidants, vitamins, and minerals. In this study, 30 isolates of local freshwater microalgae were screened first based on their growth rate to select the most suitable strains for feed production. Based on the normality test, 15 fast-growing microalgae isolates were selected and subjected to further investigation of their metabolites content. The hierarchical Cluster Analysis conducted on lipids, proteins and carbohydrates contents subdivided these strains selected into 4 clusters, among them, the cluster one was grouping three Chlorella and two Mychonastes isolates with high nutritional values due to their high amounts of lipid and protein. The survey of metabolite production was performed every three days during growth in a volume of 3 L. We observed that the maximum amount of proteins and lipids was produced at day 6 and 14, respectively. The assessment of the Trolox equivalent antioxidant capacity of the top 5 strains proved that Mychonastes homosphaera isolate QUCCCM70 showed the highest antioxidant capacity. Moreover, results revealed the presence of essential amino acids and omega3 fatty acids. The screening evidenced a Mychonastes homosphaera strain QUCCCM70 with high nutritional value that can be considered as a promising alternative to produce a well-balanced animal feed supplement for a high quality of poultry and livestock products. • Screening of 30 desert microalgae showed 15 fast growing isolates • Hierarchical Cluster Analysis of metabolites production evidenced 4 clusters • Peak time of protein and lipid production corresponds to day 6 and 14, respectively • M.homosphaera biomass exhibited essential amino acids and essential fatty acids • M.homosphaera is a promising feedstock for high quality animal feed. [ABSTRACT FROM AUTHOR]