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This paper describes a new species from the Class Chlorophyceae, Mychonastes frigidus sp. nov., isolated from a cold-water mountain stream in the north of Russia (Subpolar Ural). The taxon is described using morphological and molecular methods. Mychonastes frigidus sp. nov. belongs to the group of species of the genus Mychonastes with spherical single cells. Comparison of ITS2 rDNA sequences and its secondary structures combined with the compensatory base changes approach confirms the separation between Mychonastes frigidus sp. nov and other species of the genus. Mychonastes frigidus sp. nov. represents a cryptic species that can only be reliably identified using molecular data.

The seasonal and spatial eukaryotic phytoplankton composition in the Fenhe River was investigated based on the 18S rDNA V4 region. The relationship between phytoplankton functional groups and environmental factors was explored to effectively capture the responses of these taxa to environmental gradients and their effects on ecosystem function. Our results indicated that the Chlorophyta and Bacillariophyta had higher relative abundance than other taxa, and their diversity and richness indices in spring were higher than those in other seasons. The linear discriminant analysis effect size (LEfSe) analyses detected that the potential seasonal biomarkers included Desmodesmus, Cyclotella, Pseudoschroederia, Discostella, Scenedesmus, Monoraphidium, and Nannochloropsis; the spatial biomarkers included Amphora, Neochloris, Hindakia, Pseudomuriella, Coccomyxa, Chloroidium, Scherffelia, Chromochloris, and Scotinosphaera. The systemic evolution and distribution characteristics of the first 50 representative sequences showed that the dominant genus included Desmodesmus in spring, Pseudopediastrum in summer, Mychonastes in autumn, and Monoraphidium in winter. Main seasonal variation of phytoplankton functional groups was as follows: spring (J + F + C + X1) → summer (J + F + X1 + X2) → autumn (J + F + X1 + C) → winter (X1 + J + B + X2). Pearson correlation, redundancy analysis, and variance partitioning analysis showed temperature and phosphate were the determining factors causing the changes of phytoplankton functional groups and community composition in the Fenhe River.

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.

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.

The biodiversity of terrestrial algae is still grossly understudied, and African deserts in particular are barely touched in this respect. Here, four coccoid green algae from oases in the Western Desert of Egypt were characterized using a combination of morphotaxonomic, ecological and 18S rDNA data, with additional carotenoid and lipid analyses for two of the strains. Three strains were identified as affiliated with known taxa: Mychonastes sp., Asterarcys sp. (first report of this genus from a desert soil), and Stichococcus cf. deasonii. The fourth strain is proposed to represent a new cryptic genus Pharao gen. nov., with the type species P. desertorum sp. nov. The new taxon is sister to the clade of uncharacterized North American desert strains of Radiococcaceae (Chlorophyceae, Chlorophyta). The pigment profile of P. desertorum gen. et sp. nov. revealed carotenoids and chlorophylls typical of green algae. Bioorganic analysis showed a complex lipidome based on phospho- (PC), galacto- (MGDG and DGDG), betaine- (DGTS), and sulfoquinovosyl- (SQDG) membrane lipids, besides significant amounts of storage neutral lipids such as diacyl- (DAG) and triacylglycerols (TAG). The presence of saturated alkyl chains within all the membrane lipid classes in P. desertorum and Asterarcys sp. appears to reflect the need to maintain membrane fluidity and viscosity. In summary, African deserts likely still harbor new taxa to be described, and lipidomic analyses of such taxa may provide clues about their ability to survive in the extremely harsh desert habitats.

Studies on autotrophic picoplankton (APP; 3 μm) to low-temperature and low-light winter environment was confirmed by their higher maximum photosynthetic rate and light utilization parameter. Maximum photosynthetic rate and light saturation parameter increased significantly with both temperature and available light, but with different impact on the two size groups. Twenty-two picoeukaryotic strains were isolated and identified based on 18S rRNA gene sequence analysis. Taxonomic composition of the picoeukaryotic community in the studied shallow lakes was similar to other freshwater lakes in the temperate zone: members of genera Choricystis and Mychonastes were dominant, however, in Lake Balaton, common freshwater taxa such as Stichococcus bacillaris and Nannochloris bacillaris were also found.

Lake Poyang, which is connected to the Yangtze River, is the largest freshwater lake in China and experiences large and frequent changes in water levels. The seasonal diversity and composition of photosynthetic picoeukaryotes (PPEs) in Lake Poyang were investigated from flow-cytometry-sorted samples using MiSeq high-throughput sequencing. Flow cytometric counting indicated that PPEs accounted for 97% of the total picophytoplankton abundance in spring, reaching a maximum value of 6.30 × 104 cells mL-1. PPEs in Lake Poyang showed lower diversity than those in other investigated lakes in the lower reaches of the Yangtze River and were dominated by one OTU (66.29%) affiliated with Mychonastes (Chlorophyceae). Other minor classes of PPEs were found to be sporadically abundant in specific seasons, i.e. Chrysophyceae prevailed in spring and summer, while Eustigmatophyceae was mainly present in winter. This study reports coccal green algae of Mychonastes in Lake Poyang; additionally, these algae are reportedly representative of the prominent plankton in this river-connected lake ecosystem but are often overlooked due to their lack of morphological features. Finally, the sequencing results from the sorted samples of Lake Poyang revealed that the proportion of PPEs was quite low, with an average of 36% of total reads. Many OTUs belonging to heterotrophic picoeukaryotes were also identified in the sorted samples, most of which were affiliated with terrestrial fungi, including Basidiomycota and Ascomycota. The spores of these fungi can disperse in the aquatic environment during the flood seasons, yet their effect on PPEs is still unclear.

The first reports on the presence of zoochlorellae within the organelles of mesenchymal cells from freshwater sponges were published in the 19th century. Today, it is well-known that freshwater sponges can be found in association with different endosymbiotic algae. However, until now there has been no detailed information about the endosymbiotic chlorophyll-containing algae in the remarkable endemic green sponges from Lake Baikal. In our study we were able for the first time to isolate and identify endosymbionts from primmorphs cultivated in vitro, and to compare them with those from naturally occurring Lubomirskia baicalensis sponges. Structural as well as molecular biological investigations show that the endosymbiotic alga is a Mychonastes species closely related to M. huancayensis. Another novel aspect of our work was to show that it is possible to use primmorphs of endemic sponges for isolation and subsequent cultivation of their endosymbiotic algae. We employed a simple cold-water (3–4°C) approach fo...

The aim of this study is to evaluate the feasibility of using lipid-accumulating microalgae to remove cephalosporin antibiotics 7-amino cephalosporanic acid (7-ACA) from wastewater with the additional benefit of biofuels production. Three isolated microalgal strains (namely, Chlorella sp. Cha-01, Chlamydomonas sp. Tai-03 and Mychonastes sp. YL-02) were cultivated under 7-ACA stress and their biomass productivity, lipid production and N-NO3- consumption were monitored. It was found that 7-ACA had slight inhibition effects on the microalgal growth at the ratio of 12.0% (Cha-01), 9.6% (YL-02), 11.7% (Tai-03). However, lipid accumulation in the three microalgae was not influenced by the presence of 7-ACA. The investigation on the 7-ACA removal mechanisms during microalgal growth shows that 7-ACA was mainly removed by microalgae adsorption as well as hydrolysis and photolysis reactions. This study demonstrates that using microalgae to treat antibiotic-containing wastewater is promising due to the potential of simultaneous antibiotic removal and biofuel production.

Summary Stentor polymorphus (Muller) 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.

Coccoid green algae generally are difficult to classify because of their depauperate morphology, and for this reason many of them have a complicated taxonomic history. In the present study we use analyses of molecular sequence data to demonstrate the close relationship of two green coccoid taxa that have undergone multiple taxonomic transfers in the past, and argue for the recognition of a distinct lineage. We resurrect the genus Chromochloris to accommodate C. zofingiensis (= Muriella zofingiensis) and we provide data regarding the lineage's phylogenetic relationships to other chlorophyte genera, especially Bracteacoccus, Chlorella, Muriella, Mychonastes, and Pseudomuriella. In addition, we synonymize B. cinnabarinus and Bracteacoccus minutus with C. zofingiensis, and clarify the identity of three UTEX strains heretofore listed as Bracteacoccus.

The genus Chlorella (in its traditional sense) is polyphyletic and belongs to at least twelve independent lineages of the Trebouxiophyceae and Chlorophyceae. Most of the aquatic species belong to the Chlorella and Parachlorella clades (within the so-called Chlorella -lineage of the Trebouxiophyceae), or to the genera Scenedesmus and Mychonastes (within the DO-group of the Chlorophyceae) according to phylogenetic analyses of the SSU and ITS rDNA sequences. In contrast to the aquatic species, the terrestrial strains investigated so far form a monophyletic lineage ( Watanabea -clade) within the Trebouxia -lineage of the Trebouxiophyceae. Several genera with Chlorella -like morphology ( Chloroidium , Heterochlorella , Watanabea , Kalinella , Viridiella and others) belong to the Watanabea clade. We studied 22 strains isolated from soil, bark, and artificial hard substrates, which have been traditionally identified as Chlorella luteoviridis or as unidentified Chlorella . To clarify the taxonomical status and intrageneric diversity of this group, we used an integrated approach (molecular phylogeny of SSU and ITS rDNA sequences, secondary structures, DNA barcoding, and morphology) including the ecological distribution. All investigated strains showed a low phenotypic plasticity, but a high genetic diversity, which could be only resolved in complex phylogenetic analyses based on the secondary structures of the investigated genes. Considering these results, we reestablished the genus Jaagichlorella for Heterochlorella and Heveochlorella , and proposed new combinations ( J. luteoviridis , J. hainangensis , J. roystonensis , and J. sphaerica ) as well as the new species, J. africana .

KRIENITZ L., BOCK C., DADHEECH P.K. AND PROSCHOLD T. 2011. Taxonomic reassessment of the genus Mychonastes (Chlorophyceae, Chlorophyta) including the description of eight new species. Phycologia 50: 89-106. DOI: 10.2216/10- 15.1 The generic concept of the chlorophycean green algae Mychonastes (preferably living solitary) and Pseudodictyo- sphaerium (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.

Microphytes (Cyanobacteria and algae) are amongst the most promising sustainable resources for high-quality compounds, but high expenditures for culturing, harvesting and subsequent processing complicate their exploitation. An economic way to reduce costs of algal mass cultures is to install open-pond culture systems in tropical regions, which guarantee high solar irradiance throughout the year, but this approach is still waiting to be introduced in East Africa. One essential but often neglected requirement to carry out successful microphytean mass cultures is strain selection. We provide a selection of high-yielding microphytes with high potential for biotechnology use collected in the soda lakes and adjacent systems such as salt evaporation ponds or sewage oxidation ponds. Microphytes were detected as field clones or cultured strains and identified via microscopy and molecular methods; SSU rRNA and/or ITS sequences were entered in the NCBI database. Besides the well-known and already commercially exploited cyanobacterium Arthrospira, promising relatives of the famous “green balls” Chlorella, members of the green algal genera Selenastrum, Picocystis and Mychonastes and the eustigmatophytes Nannochloropsis and Microchloropsis are presented. All of them are suitable for ex situ conservation in strain collections, which is the basis for future mass cultivation and commercial use.

A 1-year field study monitoring depth profiles of picoplankton and physicochemical data in the oligotrophic Lake Lucerne (Switzerland) showed that picocyanobacteria play an important role in the CaCO3 precipitation process. Laboratory experiments with Mychonastes and Chlorella, isolated from Lake Lucerne and Synechococcus using ion selective electrodes, scanning electron microscopy and X-ray powder diffraction clearly demonstrated the potential of picoplankton for fast and effective CaCO3 precipitation. The combination of a field study with laboratory experiments confirmed the previous reports of picocyanobacteria triggering the CaCO3 precipitation in hardwater oligotrophic lakes. Electron micrographs of particles from the water column often reveal the size and shape of picoplankton cells covered by calcite. In addition the results from the laboratory approach indicated that algae and bacteria induced different precipitation mechanisms. Experiments with Mychonastes and Chlorella produced crystalline calci...

The Internal Transcribed Spacer I (ITS1) of the nuclear ribosomal DNA of several taxa of Chlorella and of related species of Auxenochlorella, Graesiella, Mychonastes, and Scenedesmus has been sequenced. ITS 1 length ranges from 155 (S. fuscus) to 290bp (both varieties of C. vulgaris), and GC content from 43.1% (S. obliquus) to 63.6% (C. kessleri). ITS 1 length and GC content appear to be at least strain specific. The following clusters of taxa could be recognized: a group composed by C. lobophora and C. vulgaris, a group composed by C. kessleri SAG 211-11 and C. luteoviridis SAG 211-5b as well as larger group composed by the latter four species, wich in turns cluster with C. sorokiniana; a group composed by S. fuscus and S. multiformis, a larger group containing also S. obliquus and, finally, a cluster including the three latter taxa and G. vacuolata, The results obtained in this paper indicate that identification by using ITS 1 is unequivocal at least at species level and in various cases at strain level. The heterogeneity found in ITS 1 sequences of Chlorella probably implies a very ancient separation of the various taxa, which have been kept together taxonomically on the basis of the plesiomorphic overall shape. The ITS 1 sequence data seem a fast and reliable method to classify at the species level strains of Chlorella of uncertain taxonomic position.

As Scenedesmus komarekii Hegewald was cultured under high light intensity and nitrogen limitation, the color of cells progressed from green to brown, and finally through orange to brick red. The secondary carotenoids astaxanthin and canthaxanthin, as well as apolar carotenoids, were detected in the brown and orange cells. These carotenoids were contained in lipoidal globules that were first formed at the periphery of the cell and progressively propagated toward its inside, eventually filling most of it. The chloroplast was single and parietal in the green cells. As the cells turned brown, the chloroplast divided into several small lobes and was pushed toward the interior by the accumulating lipoidal globules. Sometimes the outer layer of the wall of the brown cell developed one or two diametrically opposed swellings. Once the cells became orange or red, neither lipoidal globules nor any major organelles were distinguishable. The cell wall in the orange cells became thick because of the formation of electron-dense granules between its outer and inner layers. The mode of the secondary carotenoid accumulation in S. komarekii differs from that of Haematococcus, an alga well known for its ability to accumulate secondary carotenoids, but resembles that of “Chlorella”zofingiensis (=Mychonastes zofingiensis (Donz) Kalina et Puncochařova).

Nuclear-encoded small subunit ribosomal RNA gene (18SrDNA) sequences were determined for Coelastrella multistriata (Trenkwalder) Kalina et Puncochařova, two species of Scotiellopsis (S. oocystiformis (Lund) Kalina et Puncochařova and S. terrestris (Reisigl) Kalina et Puncochařova) and two species of Muriella (M. aurantiaca Vischer and M. terrestris Boye- Petersen). Coelastrella and Scotiellopsis are members of the subfamily Scotiellocystoideae, and Muriella is a member of the subfamily Chlorelloideae in the family Chlorellaceae. Phylogenetic trees were constructed based on these sequence data and on previously known 18SrDNA sequences of 25 taxa. Coelastrella and Scotiellopsis were closely related to each other and formed a cluster with Scenedesmus vacuolatus (Shihira et Krauss) Kessler et al. This cluster shared a monophyletic ancestry with other Scenedesmus species. Muriella aurantiaca formed a sister relationship with the monophyletic lineage of Scenedesmus. However, another species, M. terrestris, was placed in the Trebouxiophyceae and was strongly related to Chlorella. The genus Mychonastes belonging to the Scotiellocystoideae was also not monophyletic. This study suggests that the subfamily Scotiellocystoideae should be removed from the Chlorellaceae.

Colonial green algae exhibiting the Dictyosphaerium morphology are common members in freshwater habitats. They can be dominating the plankton of lakes and form blooms. The Dictyosphaerium morphotype is characterized by spherical or oval cells which are connected via gelatinous stalks and surrounded by mucilaginous envelopes. In this thesis, the diversity and phylogenetic relationships of members of the Dictyosphaerium morphotype was evaluated by combining molecular phylogenetic analyses based on SSU and ITS rRNA gene sequences, with secondary structure comparisons and morphological examinations. The molecular analyses showed a polyphyletic origin of the Dictyosphaerium morphotype within the Chlorellaceae (Trebouxiophyceae). The molecular studies demonstrated the incongruence between phylogenetic relationships and morphological classifications. Several taxa formerly grouped in different algal families clustered within the Chlorellaceae. The newly designated epitype-strain of D. ehrenbergianum was member of a new phylogenetic subclade within the Parachlorella clade of the Chlorellaceae, assigning the genus Dictyosphaerium to this clade. Next to the epitype, two new lineages evolved which resembled D. ehrenbergianum but differed in their genetic signature. According to the Compensatory Base Change (CBC) approach, these two new lineages are separate species, even if morphological criteria distinguishing them from D. ehrenbergianum are scarce. Moreover, the mucilaginous morphotype evolved in new lineages within the Chlorella and Parachlorella clades. Dictyosphaerium tetrachotomum is one of the most frequent Dictyosphaerium species in inland waters. The phylogenetic tree revealed a new subclade consisting of this morphotype within the Chlorella clade. In addition, several lineages with the spherical morphotype were detected within the Chlorella and Parachlorella clades. This high genetic range did not correspond to a high morphological distinctness, since only small morphological changes were observed between lineages. This study further revealed that the Dictyosphaerium morphotype clustered closely to Chlorella vulgaris. By applying Moniz and Kaczmarska`s barcoding system on the genus Chlorella we were able to define nine new lineages within the genus, including seven species with mucilage and colonial life form. The delineation of Chlorella species by this barcoding system was congruent with the CBC approach. The phylogenetic study further showed that the Dictyosphaerium morphotype evolved also within the Chlorophyceae. One clade containing Dictyosphaerium strains without pyrenoids clustered between members of the solitary genus Mychonastes. The phylogenetic tree revealed no clear distinction between solitary and colonial strains. Consequently, all strains were newly combined to Mychonastes. This thesis demonstrated how molecular results can reshape the classification and understanding of conceptions of genera and species in colonial and mucilaginous green algae. Similar morphological traits may be the result of convergent evolution and phenotypic adaptations to ecosystem conditions and do not have to reflect phylogenetic relationships. In addition, our results stressed the importance of thoroughly sampled and well characterized groups to serve as model systems for the construction of the green algae tree of life., Koloniale Grünalgen des Dictyosphaerium-Phänotyps sind typische Vertreter des Planktons im Süßwasser. In eutrophen Seen können sie die Zusammensetzung des Planktons dominieren. Sie sind geprägt durch runde oder ovale Zellen, die durch gallertartige Stränge miteinander verbunden und von einer Schleimhülle umgeben sind. In dieser Dissertation wurden die Diversität und die Verwandtschaftsbeziehungen des Dictyosphaerium-Phänotyps mit Hilfe eines kombinierten Ansatzes aus molekular-phylogenetischen Untersuchungen, Sekundärstrukturanalysen und morphologischen Beobachtungen evaluiert. Molekulare Untersuchungen haben gezeigt, dass der Dictyosphaerium-Phänotyp polyphyletisch innerhalb der Chlorellaceae entstanden ist. Neueste Resultate ergaben, dass Taxa mit unterschiedlichster Morphologie innerhalb der Chlorellaceae evolvierten. Durch die Designierung eines Epitypus für Dictyosphaerium ehrenbergianum konnte die Gattung Dictyosphaerium einer neuen phylogenetischen Linie im Parachlorella-Clade zugeordnet werden. Weitere phylogenetische Linien entwickelten sich neben der des Epityps, deren Stämme D. ehrenbergianum morphologisch stark ähneln. Die genetische Signatur wies CBCs innerhalb der ITS2 auf wodurch die Linien nach dem CBC Konzept unabhängigen Arten entsprechen. Molekulare Untersuchungen am D. tetrachotomum- Phänotyp zeigten eine neue Linie im Chlorella-Clade und damit wurde er einer neuen Gattung zugeordnet. Mehrere Linien mit Dictyosphaerium-artigen Phänotypen und runden Zellen konnten im Chlorella-und Parachlorella-Clade entdeckt werden, und neue Gattungen und Arten wurden beschrieben. Das hohe genetische Spektrum spiegelte sich nicht in einer morphologischen Vielfalt wieder und erschwerte eine morphologische Identifikation. Überraschenderweise wurde eine nahe Verwandtschaft des Dictyosphaerium-Phänotyps zur solitären- schleimlosen Chlorella vulgaris nachgewiesen. Durch die Anwendung des Barcoding-Systems nach Moniz und Kaczmarska wurden innerhalb der Gattung Chlorella neun neue Linien aufgezeigt, sieben davon koloniale Arten mit Schleimhülle. Die Abgrenzung der Chlorella-Arten mit Hilfe des Barcoding- Systems erfolgte übereinstimmend mit dem CBC Konzept wodurch die Gattung Chlorella emendiert werden musste um koloniale und schleimbildende Arten mit einzubeziehen. Weiterhin zeigte die Phylogenie, dass der Dictyosphaerium- Phänotyp auch innerhalb der Chlorophyceae evolvierte. Pyrenoidfreie Dictyosphaerium-Stämme formten ein gemeinsames Cluster mit solitären Vertretern der Gattung Mychonastes. Es konnte keine Gruppierung zwischen den solitären und kolonialen Stämmen aufgezeigt werden, aufgrund dessen wurden die Pseudodictyosphaerium-Arten in die Gattung Mychonastes überführt. Vorliegende Ergebnisse zeigen, in welchem Maße molekulare Resultate unser Verständnis über die Klassifizierung und die Konzepte zur Gattungs- und Artabgrenzung von kolonialen und schleimbildenden Grünalgen verändern können. Viele morphologische Merkmale sind das Resultat konvergenter Evolution und phänotypischer Anpassung an die Bedingungen im Ökosystem und stellen keine direkte phylogenetische Verwandtschaft dar. Diese Erkenntnisse verdeutlichten weiterhin die Bedeutung von gut untersuchten und genau charakterisierten Algengruppen als Modelle für die Konstruktion des Stammbaumes der Grünalgen.

Species of Mychonastes, Pseudodictyosphaerium, and Korshpalmella all have spherical (or nearly so) coccoid cells without pyrenoids. Mychonastes and Pseudodictyosphaerium are apparently frequent components of the picoplankton of lakes, although they had not been reported from North America prior to our studies. We have examined several isolates of Mychonastes, Pseudodictyosphaerium, and Korshpalmella from lakes and ponds in Itasca State Park, Minnesota (USA) and Arrowwood National Wildlife Refuge, North Dakota (USA). These isolates comprise 5 different 18S rDNA sequence types, none of which have a sequence identical to any published sequence for Mychonastes or Pseudodictyosphaerium. Four of these 18S types produce solitary cells, consistent with Mychonastes spp. However, other isolates all have identical 18S rDNA sequences, but are either unicellular, colonial with connecting stalks, or colonial in an amorphous matrix, consistent with Mychonastes spp., Pseudodictyosphaerium spp. or Korshpalmella spp, respectively. For some isolates, the colonial character is plastic, with different morphologies seen with different growth conditions. Ribosomal ITS and rbcL sequences also indicate little or no diversity among the isolates with various morphologies. These results suggest that the colonial habit is not a reliable generic character. Phylogenetic analyses of both rbcL and 18S rDNA sequences indicate that Mychonastes and Pseudodictyosphaerium spp. are a distinct lineage within the Chlorophyceae and should be placed in a new family. This material is based upon work supported by the National Science Foundation under Grant Nos. DEB-0128953, DEB-0129030, DBI-0070387 and MCB-0084188.

The coccoid algae (a.k.a ‘little green balls’) are important primary producers in freshwater communities, but very little is known about their diversity. This lack of knowledge results from the extremely small size and simple morphology of these organisms, which makes identification by light microscopy essentially impossible. However, molecular techniques allow differentiation of taxa at various levels and can ultimately lead to species identification. We have isolated several hundred cultures of coccoid algae from lakes and ponds in Itasca State Park in north-western Minnesota and Arrowwood National Wildlife Refuge in central North Dakota. Many of these isolates have been examined by light microscopy, 18S rDNA PCR–RFLP analysis, and 18S rDNA sequence analysis. In addition, some taxa with multiple isolates have been examined by rbcL and ribosomal RNA ITS sequence analysis. Our results indicate a high level of diversity, including possible new species of Chlorella, Muriella, Pseudomuriella and Mychonastes, among others. We will discuss the results of our analyses, including implications for identification of taxa and higher level systematics. Supported by National Science Foundation Grants DBI-00703867, MCB-0084188 and DEB-0128952.

The diversity of eucaryotic picoalgae in three Swiss lakes was characterized by light microscopy and these observations were compared with analyses of SSU rDNA sequences. The phylogenetic analyses suggested that seven of the eight investigated strains were either related to Choricystis (Trebouxiophyceae) or Mychonastes (Chlorophyceae). Light microscopic analyses revealed that strains belonging to these two lineages could not be discriminated using morphological characters such as cell morphology, cell shape or growth habit. A single strain which was characterized by the presence of pyrenoids turned out to be closely related to Chlorella sp. The common opinion that eucaryotic freshwater picoalgae are either related to Nannochloris or Chlorella cannot be hold any longer.

A new monotypic genus of the Chlorophyceae isolated from brackish water of the Chesapeake Bay, Maryland, U.S.A. is described as Mychonastes ruminatus. The alga is compared with similar members of the Oocystaceae. Based on the presence of a thick ruminate cell wall, the lack of discernible pyrenoids, and other vegetative characters, Mychonastes can be delineated from other green coccoid unicells. The cellular life cycle of Mychonastes was studied by electron microscopy and compared to published studies of Chlorella. The genera are differentiated by wall and chloroplast structure. Mychonastes cell wall is sculptured and changes during the life cycle from a highly irregular appearance when young, to a less irregular state when mature. Mychonastes chloroplast lacks pyrenoids at all times. Chlorella has a smooth wall and pyrenoids which are apparent just after release from the mother cell until division. Organelles of both genera migrate in a similar pattern throughout the life cycle, with Mychonastes producin...

Optimal growth conditions of temperature, light and salinity were determined for Mychonastes ruminatus. At a light intensity of 1·9 mW cm-2 (28,600 lx) in 15‰. salinity medium, the alga grew at temperatures between 5·0°C and 30·0°C with a maximal doubling rate of 1·67/day at 25·0°C. Light saturation at 25·0°C was 0·78 mW/cm2 (11,750 lx) at 15‰. salinity. These values for optimal temperature and light saturation are similar to those obtained for other Chlorophycean algae. The effect of salinity on growth rates has been studied primarily on marine Chrysophytes and seaweeds with few reports for green unicellular algae. Mychonastes ruminatus grew in salinities between 1·0 and 30·0‰.. Growth declined below 10·0‰. and above 20·0‰. and was nearly constant between these salinities. The mechanisms of salt tolerance in algal cells are discussed with special reference to the suitability of M. ruminatus to test the theory of an ATPase mediated K+ pump.

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.