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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.

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 ...

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...

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.

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...

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.