Assessing morphological congruence in Dinobryon species and their stomatocysts, including a newly established Dinobryon pediforme-stomatocyst connection.

The chrysophyte genus Dinobryon Ehrenberg consists of 44 taxa, which occur in freshwaters, rarely marine waters, mostly in temperate regions of the world. The taxa of Dinobryon produce characteristic solitary or dendroid colonies and resting stages called stomatocysts. Only 20 Dinobryon taxa have information on produced stomatocysts and only four stomatocysts are reliably linked with vegetative stages using modern identification standards employing scanning electron microscopy (SEM) analyses. In this study, an encysted material of Dinobryon pediforme (Lemmermann) Steinecke was collected in two lakes in contrasting regions of Poland. Light microscopy (LM) and scanning electron microscopy (SEM) analyses revealed that Dinobryon pediforme produces stomatocyst #61, Piatek J. that is described here as new morphotype following the International Statospore Working Group (ISWG) guidelines. This raises to five the number of reliable links between vegetative stages of Dinobryon species and corresponding stomatocysts. Phenotypic similarities between Dinobryon species and their stomatocysts, analysed for five reliably established links, showed no relationships in size and shape between loricas and stomatocysts belonging to the same species. The morphological characters of loricas and stomatocysts mapped onto the phylogenetic tree of the five Dinobryon species revealed only little congruence between their morphology and phylogenetic relationships.

Intraspecific Variation in Protists: Clues for Microevolution from Poteriospumella lacustris (Chrysophyceae).

Species delimitation in protists is still a challenge, attributable to the fact that protists are small, difficult to observe and many taxa are poor in morphological characters, whereas most current phylogenetic approaches only use few marker genes to measure genetic diversity. To address this problem, we assess genome-level divergence and microevolution in strains of the protist Poteriospumella lacustris, one of the first free-living, nonmodel organisms to study genome-wide intraspecific variation. Poteriospumella lacustris is a freshwater protist belonging to the Chrysophyceae with an assumed worldwide distribution. We examined three strains from different geographic regions (New Zealand, China, and Austria) by sequencing their genomes with the Illumina and PacBio platforms. The assembled genomes were small with 49-55 Mb but gene-rich with 16,000-19,000 genes, of which ∼8,000 genes could be assigned to functional categories. At least 68% of these genes were shared by all three species. Genetic variation occurred predominantly in genes presumably involved in ecological niche adaptation. Most surprisingly, we detected differences in genome ploidy between the strains (diploidy, triploidy, and tetraploidy). In analyzing intraspecific variation, several mechanisms of diversification were identified including SNPs, change of ploidy and genome size reduction.

High planktonic diversity in mountain lakes contains similar contributions of autotrophic, heterotrophic and parasitic eukaryotic life forms.

A rich eukaryotic planktonic community exists in high-mountain lakes despite the diluted, oligotrophic and cold, harsh prevailing conditions. Attempts of an overarching appraisal have been traditionally hampered by observational limitations of small, colorless, and soft eukaryotes. We aimed to uncover the regional eukaryotic biodiversity of a mountain lakes district to obtain general conclusions on diversity patterns, dominance, geographic diversification, and food-web players common to oligotrophic worldwide distributed freshwater systems. An unprecedented survey of 227 high-altitude lakes comprising large environmental gradients was carried out using Illumina massive tag sequencing of the 18S rRNA gene. We observed a large Chrysophyceae dominance in richness, abundance and novelty, and unveiled an unexpected richness in heterotrophic phagotrophs and parasites. In particular, Cercozoa and Chytridiomycota showed diversity features similar to the dominant autotrophic groups. The prominent beta-dispersion shown by parasites suggests highly specific interactions and a relevant role in food webs. Interestingly, the freshwater Pyrenean metacommunity contained more diverse specific populations than its closest marine oligotrophic equivalent, with consistently higher beta-diversity. The relevance of unseen groups opens new perspectives for the better understanding of planktonic food webs. Mountain lakes, with remarkable environmental idiosyncrasies, may be suitable environments for the genetic diversification of microscopic eukaryotic life forms.

Community structure of photosynthetic picoeukaryotes differs in lakes with different trophic statuses along the middle-lower reaches of the Yangtze River.

Photosynthetic picoeukaryotes (PPEs) play an important role in aquatic ecosystem functioning. There is still a relative lack of information on freshwater PPEs, especially in eutrophic lakes. We used a combination of flow cytometric sorting and pyrosequencing to investigate the PPEs community structure in more than 20 mesotrophic and eutrophic lakes along the middle-lower reaches of the Yangtze River in China. The abundance of PPEs ranged between 2.04 × 103 and 5.92 × 103 cells mL-1. The contribution of PPEs to total picophytoplankton abundance was generally higher in eutrophic lakes than in mesotrophic lakes. The sequencing results indicated that the Shannon diversity of PPEs was significantly higher in mesotrophic lakes than in eutrophic lakes. At the class level, PPEs were mainly dominated by three taxonomic groups, including Cryptophyceae, Coscinodiscophyceae and Chlorophyceae, and 15 additional known phytoplankton classes, including Synurophyceae, Dinophyceae, Chrysophyceae, Trebouxiophyceae and Prymnesiophyceae, were identified. Coscinodiscophyceae dominated in the most eutrophic lakes, while Chrysophyceae, Dinophyceae and other classes of PPEs were more abundant in the mesotrophic lakes. We also observed several PPEs operational taxonomic units, and those affiliated with Cyclotella atomus, Chlamydomonas sp. and Poterioochromonas malhamensis tended to be more prevalent in the eutrophic lakes. The canonical correspondence analysis and Mantel analysis highlighted the importance of environmental parameters as key drivers of PPEs community composition.

High-throughput sequencing of microbial eukaryotes in Lake Baikal reveals ecologically differentiated communities and novel evolutionary radiations.

We performed high-throughput 18S rDNA V9 region sequencing analyses of microeukaryote (protist) communities at seven sites with depths ranging from 0 to 1450 m in the southern part of Lake Baikal. We show that microeukaryotic diversity differed according to water column depth and sediment depth. Chrysophytes and perkinsids were diverse in subsurface samples, novel radiations of petalomonads and Ichthyobodo relatives were found in benthic samples, and a broad range of divergent OTUs were detected in deep subbenthic samples. Members of clades usually associated with marine habitats were also detected, including syndineans for the first time in freshwater systems. Fungal- and cercozoan-specific c. 1200 bp amplicon clone libraries also revealed many novel lineages in both planktonic and sediment samples at all depths, a novel radiation of aphelids in shallower benthic samples, and partitioning of sarcomonad lineages in shallow vs deep benthic samples. Putative parasitic lineages accounted for 12.4% of overall reads, including a novel radiation of Ichthyobodo (fish parasite) relatives. Micrometazoans were also analysed, including crustaceans, rotifers and nematodes. The deepest (>1000 m) subsurface sediment samples harboured some highly divergent sequence types, including heterotrophic flagellates, parasites, putative metazoans and sequences likely representing organisms originating from higher up in the water column.

Small but Manifold - Hidden Diversity in "Spumella-like Flagellates".

Colourless, nonscaled chrysophytes comprise morphologically similar or even indistinguishable flagellates which are important bacterivors in water and soil crucial for ecosystem functioning. However, phylogenetic analyses indicate a multiple origin of such colourless, nonscaled flagellate lineages. These flagellates are often referred to as "Spumella-like flagellates" in ecological and biogeographic studies. Although this denomination reflects an assumed polyphyly, it obscures the phylogenetic and taxonomic diversity of this important flagellate group and, thus, hinders progress in lineage- and taxon-specific ecological surveys. The smallest representatives of colourless chrysophytes have been addressed in very few taxonomic studies although they are among the dominant flagellates in field communities. To overcome the blurred picture and set the field for further investigation in biogeography and ecology of the organisms in question, we studied a set of strains of specifically small, colourless, nonscaled chrysomonad flagellates by means of electron microscopy and molecular analyses. They were isolated by a filtration-acclimatisation approach focusing on flagellates of around 5 µm. We present the phylogenetic position of eight different lineages on both the ordinal and the generic level. Accordingly, we describe the new genera Apoikiospumella, Chromulinospumella, Segregatospumella, Cornospumella and Acrispumella Boenigk et Grossmann n. g. and different species within them.

Metagenomic Analyses of White Sea Picoalgae: First Data.

Picoalgae (defined as cells smaller than 2-3 µm) include members of diverse taxonomic groups. They are an important constituent of marine plankton and ice biota and play a significant ecological role in biogeochemical cycles. Despite their importance, the true extent of their diversity has only recently been uncovered by molecular surveys. The diversity of picoeukaryotes has not yet been studied in the White Sea, which is a unique marine environment combining features of temperate and Arctic seas. Here, we investigated the taxonomic composition of eukaryotic picoalgae in ice and under-ice water at a station located in the Kandalaksha Bay of the White Sea. We applied metagenomic survey using Illumina sequencing. Eight main algae phyla, namely, Chlorophyta, Katablepharidophyta, Haptophyta, Dinophyta, Cercozoa, Bacillariophyta, Cryptophyta, and Ochrophyta were identified. The genera Paraphysomonas and Micromonas and the order Pedinellales were most numerous in plankton; the genera Paraphysomonas, Micromonas, and Metopion were most abundant in ice. The number of "rare" phylotypes was 80 in under-ice water and 112 in ice. Some taxa of nano- and microalgae are identified for the first time in the White Sea phytoplankton. Our data provide a basis for further research of tiny phototrophs in the Russian Arctic.

Scale evolution in Paraphysomonadida (Chrysophyceae): Sequence phylogeny and revised taxonomy of Paraphysomonas, new genus Clathromonas, and 25 new species.

Heterotrophic chrysomonads of the genus Paraphysomonas are ubiquitous phagotrophs with diverse silica scale morphology. Over 50 named species have been described by electron microscopy from uncultured environmental samples. Sequence data exist for very few, but the literature reveals misidentification or lumping of most previously sequenced. For critically integrating scale and sequence data, 59 clonal cultures were studied light microscopically, by sequencing 18S ribosomal DNA, and recording scale morphology by transmission electron microscopy. We found strong congruence between variations in scale morphology and rDNA sequences, and unexpectedly deep genetic diversity. We now restrict Paraphysomonas to species with nail-like spine scales, establishing 23 new species and eight subspecies (Paraphysomonadidae). Species having base-plates with dense margins form three distinct subclades; those with a simple margin only two. We move 29 former Paraphysomonas species with basket scales into a new genus, Clathromonas, and describe two new species. Clathromonas belongs to a very distinct rDNA clade (Clathromonadidae fam. n.), possibly distantly sister to Paraphysomonas. Molecular and morphological data are mutually reinforcing; both are needed for evaluating paraphysomonad diversity and confirm excessive past lumping. Former Paraphysomonas species with neither nail-like nor basket scales are here excluded from Paraphysomonas and will be assigned to new genera elsewhere.

Effects of long-term differential fertilization on eukaryotic microbial communities in an arable soil: a multiple barcoding approach.

To understand the fine-scale effects of changes in nutrient availability on eukaryotic soil microorganisms communities, a multiple barcoding approach was used to analyse soil samples from four different treatments in a long-term fertilization experiment. We performed PCR amplification on soil DNA with primer pairs specifically targeting the 18S rRNA genes of all eukaryotes and three protist groups (Cercozoa, Chrysophyceae-Synurophyceae and Kinetoplastida) as well as the ITS gene of fungi and the 23S plastid rRNA gene of photoautotrophic microorganisms. Amplicons were pyrosequenced, and a total of 88,706 quality filtered reads were clustered into 1232 operational taxonomic units (OTU) across the six data sets. Comparisons of the taxonomic coverage achieved based on overlapping assignment of OTUs revealed that half of the eukaryotic taxa identified were missed by the universal eukaryotic barcoding marker. There were only little differences in OTU richness observed between organic- (farmyard manure), mineral- and nonfertilized soils. However, the community compositions appeared to be strongly structured by organic fertilization in all data sets other than that generated using the universal eukaryotic 18S rRNA gene primers, whereas mineral fertilization had only a minor effect. In addition, a co-occurrence based network analysis revealed complex potential interaction patterns between OTUs from different trophic levels, for example between fungivorous flagellates and fungi. Our results demonstrate that changes in pH, moisture and organic nutrients availability caused shifts in the composition of eukaryotic microbial communities at multiple trophic levels.

Primer pairs for the specific environmental detection and T-RFLP analysis of the ubiquitous flagellate taxa Chrysophyceae and Kinetoplastea.

Bacterivorous protists play a key role in microbial soil food webs, however due to the lack of specific PCR protocols targeting selected protist taxa, knowledge on the diversity and dynamics of these groups is scarce. We developed specific PCR primers in combination with a T-RFLP protocol for the cultivation-independent analysis of two important taxa of bacterivorous flagellates, the Chrysophyceae and Kinetoplastea, in soil samples. Sequence analysis of clone libraries originating from two soils in temperate regions demonstrated the specificity of the respective primer pairs. Clone sequences affiliating to the Chrysophyceae mainly clustered within the clade C2, which has been known so far for its presence mainly in cold climatic regions, whereas Kinetoplastea sequences were mainly related to the Neobodonid clade. Based on an in silico restriction analysis of database sequence entries, suitable restriction enzymes for a T-RFLP approach were selected. This in silico approach revealed the necessity to use a combination of two restriction enzymes for T-RFLP analysis of the Chrysophyceae. Soil T-RFLP profiles reflected all T-RFs of the clone library sequences obtained from the same soils and allowed to distinguish flagellate communities from different sites. We propose to use these primer pairs for PCR detection and rapid fingerprint screening in environmental samples and envisage their use also for quantitative PCR or next generation sequencing approaches.

A global perspective on marine photosynthetic picoeukaryote community structure.

A central goal in ecology is to understand the factors affecting the temporal dynamics and spatial distribution of microorganisms and the underlying processes causing differences in community structure and composition. However, little is known in this respect for photosynthetic picoeukaryotes (PPEs), algae that are now recognised as major players in marine CO2 fixation. Here, we analysed dot blot hybridisation and cloning-sequencing data, using the plastid-encoded 16S rRNA gene, from seven research cruises that encompassed all four ocean biomes. We provide insights into global abundance, α- and ß-diversity distribution and the environmental factors shaping PPE community structure and composition. At the class level, the most commonly encountered PPEs were Prymnesiophyceae and Chrysophyceae. These taxa displayed complementary distribution patterns, with peak abundances of Prymnesiophyceae and Chrysophyceae in waters of high (25:1) or low (12:1) nitrogen:phosphorus (N:P) ratio, respectively. Significant differences in phylogenetic composition of PPEs were demonstrated for higher taxonomic levels between ocean basins, using Unifrac analyses of clone library sequence data. Differences in composition were generally greater between basins (interbasins) than within a basin (intrabasin). These differences were primarily linked to taxonomic variation in the composition of Prymnesiophyceae and Prasinophyceae whereas Chrysophyceae were phylogenetically similar in all libraries. These data provide better knowledge of PPE community structure across the world ocean and are crucial in assessing their evolution and contribution to CO2 fixation, especially in the context of global climate change.

Impact of protist grazing on a key bacterial group for biogeochemical cycling in Baltic Sea pelagic oxic/anoxic interfaces.

Barrier zones between oxic and anoxic water masses (redoxclines) host highly active prokaryotic communities with important roles in biogeochemical cycling. In Baltic Sea pelagic redoxclines, Epsilonproteobacteria of the genus Sulfurimonas (subgroup GD17) have been shown to dominate chemoautotrophic denitrification. However, little is known on the loss processes affecting this prokaryotic group. In the present study, the protist grazing impact on the Sulfurimonas subgroup GD17 was determined for suboxic and oxygen/hydrogen sulphide interface depths of Baltic Sea redoxclines, using predator exclusion assays and bacterial amendment with the cultured representative 'Sulfurimonas gotlandica' strain GD1. Additionally, the principal bacterivores were identified by RNA-Stable Isotope Probing (RNA-SIP). The natural Sulfurimonas subgroup GD17 population grew strongly under oxygen/hydrogen sulphide interface conditions (doubling time: 1-1.5 days), but protist grazing could consume the complete new cell production per day. In suboxic samples, little or no growth of Sulfurimonas subgroup GD17 was observed. RNA-SIP identified five active grazers, belonging to typical redoxcline ciliates (Oligohymenophorea, Prostomatea) and globally widespread marine flagellate groups (MAST-4, Chrysophyta, Cercozoa). Overall, we demonstrate for the first time that protist grazing can control the growth, and potentially the vertical distribution, of a chemolithoautotrophic key-player of oxic/anoxic interfaces.

Ecological and evolutionary genomics of marine photosynthetic organisms.

Environmental (ecological) genomics aims to understand the genetic basis of relationships between organisms and their abiotic and biotic environments. It is a rapidly progressing field of research largely due to recent advances in the speed and volume of genomic data being produced by next generation sequencing (NGS) technologies. Building on information generated by NGS-based approaches, functional genomic methodologies are being applied to identify and characterize genes and gene systems of both environmental and evolutionary relevance. Marine photosynthetic organisms (MPOs) were poorly represented amongst the early genomic models, but this situation is changing rapidly. Here we provide an overview of the recent advances in the application of ecological genomic approaches to both prokaryotic and eukaryotic MPOs. We describe how these approaches are being used to explore the biology and ecology of marine cyanobacteria and algae, particularly with regard to their functions in a broad range of marine ecosystems. Specifically, we review the ecological and evolutionary insights gained from whole genome and transcriptome sequencing projects applied to MPOs and illustrate how their genomes are yielding information on the specific features of these organisms.

Genetic diversity of planktonic eukaryotes in high mountain lakes (Central Pyrenees, Spain).

The genetic diversity of planktonic eukaryotic microorganisms (size range 3-40 µm) inhabiting 11 alpine lakes of the Central Pyrenees (Spain) was analysed by cloning and sequencing of the 18S rRNA gene. The selected lakes covered a wide range of environmental conditions representative of the regional landscape heterogeneity. Overall, we obtained 953 sequences (averaged length 750 bp) that were grouped in 343 representative OTUs (98% identity). The genetic richness was high, and the 18S rRNA gene sequences spread within nine high-rank taxonomic groups and grouped in 26 eukaryal classes. Most of the sequences affiliated with Stramenopiles (> 55% of total sequences, mostly Chrysophyceae), Cryptophyta and Alveolata (15% each). Three groups had relative abundance < 5%, i.e. Opisthokonta (mostly Fungi), Viridiplantae (mostly Chlorophyceae) and Rhizaria (cercomonads). Finally, minor groups were related to Katablepharidophyta, Euglenozoa and Telonemida. The lakes showed a different community structure being pH, and phosphorous and Chl a concentrations the main environmental drivers. The novelty level was high, and a quarter of the retrieved OTUs were notably divergent (< 97% identity) from any previously known sequence, mainly for Rhizaria and Opisthokonta. More than 50% of the sequences affiliated with clusters exclusively formed by uncultured protists. Cryptophyta and Viridiplantae showed the largest number of sequences closely related to cultured counterparts. This work is the first description of the genetic diversity of eukaryotic assemblages in ultraoligotrophic high mountain lakes, and the study unveils alpine environments as an important reservoir of microbial eukaryotic biodiversity.

Unveiling in situ interactions between marine protists and bacteria through single cell sequencing.

Heterotrophic protists are a highly diverse and biogeochemically significant component of marine ecosystems, yet little is known about their species-specific prey preferences and symbiotic interactions in situ. Here we demonstrate how these previously unresolved questions can be addressed by sequencing the eukaryote and bacterial SSU rRNA genes from individual, uncultured protist cells collected from their natural marine environment and sorted by flow cytometry. We detected Pelagibacter ubique in association with a MAST-4 protist, an actinobacterium in association with a chrysophyte and three bacteroidetes in association with diverse protist groups. The presence of identical phylotypes among the putative prey and the free bacterioplankton in the same sample provides evidence for predator-prey interactions. Our results also suggest a discovery of novel symbionts, distantly related to Rickettsiales and the candidate divisions ZB3 and TG2, associated with Cercozoa and Chrysophyta cells. This study demonstrates the power of single cell sequencing to untangle ecological interactions between uncultured protists and prokaryotes.

A preliminary study on automated freshwater algae recognition and classification system.

BACKGROUND: Freshwater algae can be used as indicators to monitor freshwater ecosystem condition. Algae react quickly and predictably to a broad range of pollutants. Thus they provide early signals of worsening environment. This study was carried out to develop a computer-based image processing technique to automatically detect, recognize, and identify algae genera from the divisions Bacillariophyta, Chlorophyta and Cyanobacteria in Putrajaya Lake. Literature shows that most automated analyses and identification of algae images were limited to only one type of algae. Automated identification system for tropical freshwater algae is even non-existent and this study is partly to fill this gap. RESULTS: The development of the automated freshwater algae detection system involved image preprocessing, segmentation, feature extraction and classification by using Artificial neural networks (ANN). Image preprocessing was used to improve contrast and remove noise. Image segmentation using canny edge detection algorithm was then carried out on binary image to detect the algae and its boundaries. Feature extraction process was applied to extract specific feature parameters from algae image to obtain some shape and texture features of selected algae such as shape, area, perimeter, minor and major axes, and finally Fourier spectrum with principal component analysis (PCA) was applied to extract some of algae feature texture. Artificial neural network (ANN) is used to classify algae images based on the extracted features. Feed-forward multilayer perceptron network was initialized with back propagation error algorithm, and trained with extracted database features of algae image samples. System's accuracy rate was obtained by comparing the results between the manual and automated classifying methods. The developed system was able to identify 93 images of selected freshwater algae genera from a total of 100 tested images which yielded accuracy rate of 93%. CONCLUSIONS: This study demonstrated application of automated algae recognition of five genera of freshwater algae. The result indicated that MLP is sufficient, and can be used for classification of freshwater algae. However for future studies, application of support vector machine (SVM) and radial basis function (RBF) should be considered for better classifying as the number of algae species studied increases.

Emerging diversity within chrysophytes, choanoflagellates and bicosoecids based on molecular surveys.

In recent years, a substantial amount of data on aquatic protists has been obtained from culture-independent molecular approaches, unveiling a large diversity and the existence of new lineages. However, sequences affiliated with minor groups (in terms of clonal abundance) have often been under-analyzed, and this hides a potentially relevant source of phylogenetic information. Here we have searched public databases for 18S rDNA sequences of chrysophytes, choanoflagellates and bicosoecids retrieved from molecular surveys of protists. These three groups are often considered to account for most of the heterotrophic flagellates, an important functional component in microbial food webs. They represented a significant fraction of clones in freshwater studies, whereas their relative clonal abundance was low in marine studies. The novelty displayed by this dataset was notable. Most environmental sequences were distant to sequences of cultured organisms, indicating a significant bias in the representation of taxa in culture. Moreover, they were often distant to sequences from other molecular surveys, suggesting an insufficient sequencing effort to characterize the in situ diversity of these groups. Phylogenetic trees with complete sequences present the most accurate representation of the diversity of these groups, with the emergence of several new clades formed exclusively by environmental sequences. Exhaustive data mining in sequence databases allowed the identification of new diversity hidden inside chrysophytes, choanoflagellates and bicosoecids.

Structure of loricae and stalks of several bacterivorous chrysomonads (chrysophyceae): taxonomical importance and possible ecological significance.

Stalks and loricae of chrysomonads were studied by fluorescence microscopy employing Calcoflor White-Evans blue (CW-Eb) staining, and by uranyl acetate staining of dried, whole mount preparations for electron microscopy. These structures were composed of microfibrils approximately 4 nm in diameter embedded in a matrix. The organization of the loricae of Poterioochromonas malhamenesis, "Amimonas minuta", Poterioochromonas stipitata and Ochromonas gloeopara showed a similar structural plan, consisting of a foot, stalk and cup region that together resemble a wine glass. CW-Eb-stained, microfibrillar stalks were identified also in Paraphysomonas vestita, Anthophysa vegetans and "Felimonas flocculans". These results suggest that CW-Eb-stained structures composed of microfibrils approximately 4 nm in diameter may be more common in chrysomonads than previously recognized. In cultures, these structures participate in the formation of cell aggregates and attachment of cells to substrates, and thus may be of ecological importance. Additionally, non-siliceous, CW-Eb-stained cysts were identified for the first time in P. malhamensis.

Multigene evidence for the placement of a heterotrophic amoeboid lineage Leukarachnion sp. among photosynthetic stramenopiles.

The colorless amoeboid eukaryote genus Leukarachnion represents one of a long list of microbial lineages for which there have been few taxonomic studies. In this study, we analyze molecular data to assess the placement of a species of Leukarachnion on the eukaryotic tree of life and we report fine structural data to provide additional information on the identity of this taxon. Our multigene analyses indicate that Leukarachnion sp. (ATCC PRA-24) is a member of the stramenopiles, sister to the Chrysophyceae/Synurophyceae clade. It also forms a sister group relationship to the clade containing Chlamydomyxa labyrinthuloides and Synchroma grande, both of which are characterized by net-like amoeboid phases. Leukarachnion sp. and Chlamydomyxa labyrinthuloides also share fine structural cyst morphology such as bilayered structure of the cyst wall. The amoeboid form and heterotrophic habit of Leukarachnion sp. highlight the multiple origins of diverse body forms and multiple plastid losses within the stramenopiles.

Isolation of a Poterioochromonas capable of feeding on Microcystis aeruginosa and degrading microcystin-LR.

Algal blooms have become a worldwide issue recently, especially those comprised of toxic cyanobacteria. Grazers' predation of bloom-forming algae plays an important role in water clearing. In this study, a species of golden alga (strain ZX1), capable of feeding on the toxic cyanobacteria Microcystis aeruginosa, was isolated and identified as Poterioochromonas sp. (GenBank accession: EU586184) on the basis of morphological characteristics and 18s rRNA gene sequencing. Feeding experiments showed that ZX1 could clear high densities of M. aeruginosa (7.3 x 10(5)-4.3 x 10(6) cells mL(-1)) in a short time (40 h), with inhibition ratios higher than 99.9%. ZX1 grew during the feeding processes and achieved a maximum density of 10-20% of the initial M. aeruginosa density. Furthermore, this study is the first to report that ZX1 was able to degrade microcystin-LR (MC-LR) in cells of M. aeruginosa while digesting the whole cells, and that the degradation process was determined to be carried out inside the ZX1 cell. For a total MC-LR (intra- and extracellular) concentration of up to 114 microg L(-1), 82.7% was removed in 40 h. This study sheds light on the importance of golden alga in aquatic microbial ecosystems and in the natural transportation/transformation of MC-LR.