Chrysophyceae from freshwater localities near Nijmegen,The Netherlands. II.

Investigations have been carried out on the presence and abundancy of Synuraceae (Chrysophyceae) in seven freshwater bodies in the neighbourhood of Nijmegen, The Netherlands. Forty-nine taxa have been recorded of which 4 taxa concern first published records from The Netherlands. Two taxa of Mallomonopsis, five taxa of Mallomonas, one taxon of Spiniferomonas and two taxa of Paraphysomonas could not be identified. These taxa may concern undescribed species.Samples taken in April and August revealed a clear preference of most taxa for April at every sampling place, except for Molenwiel. Temperature could be the controlling factor. Most taxa have been found in Geuldert (41) and St. Jansberg (22) both in April. The great difference in the number of taxa at those two sites between both sampling data must be attributed to unusual environmental changes.     

Records of chrysophytes with siliceous scales (Mallomonadaceae and Paraphysomonadaceae) from Finnish inland waters

Seventy-three taxa of silica-scaled chrysophytes were found with LM and TEM in 264 samples from 141 Finnish water bodies, including the genera Mallomonas (40 taxa), Synura (9), Chrysosphaerella (3), Spiniferomonas (8) and Paraphysomonas (13). More than half of the taxa are recorded for the first time from Finland and five (Mallomonas actinoloma v. actinoloma, M. favosa, M. mangofera f. gracilis, M. scrobiculata and Spiniferomonas serrata) are new to Europe. Most taxa are illustrated with TEM micrographs and the taxonomy of some interesting species is discussed in detail. The seasonal occurrence of the commonest species is described.     

Freshwater scaled chrysophytes,heliozoa and thaumatomonad flagellates from Edo State,Nigeria

A total of nine silica-scaled chrysophytes (Chrysophyceae: two species each in Spiniferomonas and Paraphysomonas; Synurophyceae: five Mallomonas species), 16 heliozoa, and two scaled flagellates were recorded from 19 samples collected from Edo State, Nigeria, over a period covering both dry and rainy seasons in 2006–2007. Identifications were based on transmission electron microscopy. Eleven are new records for Africa, including a new species of Mallomonas, M. cribridomus. Also observed were two siliceous scaled colourless free-living thaumatomonad flagellates, Thaumatomastix nigeriensis and Gyromitus limax, the latter also a new record for Africa.     

Studies on generaMallomonas andSynura,and other plankton in freshwater with the electron microscope VIII. On three new species of chrysophyceae

Three new species (Chrysophyceae) which belong to the Torquata group of the genusMallomonas, to the Spinosa group of the genusSynura, and to the genusOhromonas were found from freshwater in the North-East of Japan by the aid of an electron microscope. They were namedMallomonas recticostata, Synura mammillosa, andOchromonas diademifera, respectively. The characteristics of the three new species are described here.     

THE OCCURRENCE OF CHLOROPHYLLS C1 AND C2 IN THE CHRYSOPHYCEAE1

We analyzed 34 strains representing 25 species of Chrysophyceae for chlorophylls c₁ and c₂ using thin-layer chromatography. Most organisms had both chlorophylls c₁ and c₂ in addition to chlorophyll a but 17 strains of 9 species of Synura and Mallomonas possessed only chlorophylls a and c₁. These are the first chlorophyll c-bearing algae which lack chlorophyll c₂. We postulate that at least some of the silica-scaled algae including Mallomonas and Synura may be distinct from other Chrysophyceae based upon pigmentation and other characters described in the literature.     

Mallomonadacean (Chrysophyceae) Scales: Early biotic paleoindicators of lake acidification

17 subfossil mallomonadacean species have been detected in the acidified Kleiner Arbersee. The most abundant one is M. crassisquama. In the top most layers, it is replaced by acid tolerant Synura spp. and several acidophilic and acidobiontic Mallomonas spp. Mallomonadaceae respond to acidification (and alkalinization) of lakes prior to benthic diatoms. Mallomonadaceae live euplanktically and mainly in spring, when most of the annual acid loading enters the lakes.     

Developments in the taxonomy of silica‐scaled chrysophytes – from morphological and ultrastructural to molecular approaches

Taxonomy in silica‐scaled chrysophytes has gone through three morphological phases. From primary studies of the cell morphology in the 18th century, the focus was in the 20th century replaced by studies of the silica structures of the cell envelope. Now, in the latest decades the importance of DNA sequencing has been recognized, not only to support the taxonomic framework but also to obtain new understanding of taxonomic relations among particular taxa. In the first part of this review, we provide a historical overview of the developments in the taxonomy of scale‐bearing chrysophytes. In the second part, we present a phylogenetic reconstruction of chrysophyte algae, updated by newly obtained SSU rDNA and rbcL sequences of several isolated Synura, Mallomonas and Chrysosphaerella species. We detected significant incongruence between the phylogenies obtained from the different datasets, with the SSU rDNA phylogram being the most congruent with the morphological data. Significant saturation of the first rbcL codon position could indicate the presence of positive selection in the rbcL dataset. Within the Synurales, the relationships revealed by the phylogenetic analyses highlight the artificial infragenetic classification of Mallomonas and Synura, and the occurrence of cryptic diversity within a number of traditionally defined species. Finally, three new combinations are proposed based on the phylogenetic analyses: Tessellaria lapponica, Synura asmundiae and S. bjoerkii.     

Multigene phylogeny of Synura (Synurophyceae) and descriptions of four new species based on morphological and DNA evidence

We used phylogenetic analyses based on multiple gene sequences (partial nr SSU and LSU rDNA, partial pt LSU rDNA, psaA and rbcL) from 148 strains (including three outgroups) and scale ultrastructure to examine phylogenetic relationships among species of the colonial genera Synura and Tessellaria. The phylogenetic tree based on the combined dataset was congruent with ultrastructural characteristics of the scales. Synura was divided into three major clades, two including species in section Synura, and one representing section Peterseniae. One clade, consisting of seven strains of S. uvella (section Synura), diverged at the base of the genus. The second clade consisted of the remaining species belonging to the section Synura. The third clade, containing organisms in the section Peterseniae and characterized by scales possessing a keel, was monophyletic with strong support values. Based on our findings, S. uvella needs to be in a separate section from other spine-bearing species, and we therefore propose new sectional ranks; Synura, Peterseniae, Curtispinae (presence of body scales with slender spines, tubular scales and caudal scales). We further propose four new species based on phylogenetic analyses and unique scale characters: S. longitubularis sp. nov., S. sungminbooi sp. nov., S. soroconopea sp. nov. and S. lanceolata sp. nov. Lastly, we propose a new genus name, Neotessella, to replace the invalid use of the name Tessellaria.     

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.     

STUDIES ON ULTRASTRUCTURE AND THREE‐GENE PHYLOGENY OF THE GENUS MALLOMONAS (SYNUROPHYCEAE)1

The genus Mallomonas, a common and often abundant member of the planktic community in many freshwater habitats worldwide, consists of 180 species divided into 19 sections and 23 series. Classification of species is based largely on ultrastructural characteristics of the siliceous scales and bristles that collectively form a highly organized covering over the cell. However, the relative importance of the different siliceous features of the scales, such as the dome, V rib, and secondary structures, as well as the different types of scales, in understanding the evolution and phylogeny of the genus is little known. In this study, we investigated the scale and bristle ultrastructure, along with sequences of three genes, for 19 isolates (18 species) of Mallomonas (18 isolates were from Korean habitats). The isolates represented nine of the 19 sections. Sequences for both the nuclear SSU and LSU rDNA and plastid LSU of RUBISCO (rbcL) genes for each of the 19 Mallomonas isolates and four outgroups were determined. Bayesian and maximum‐likelihood (ML) analyses of the data revealed that Mallomonas consists of two strongly supported clades. Mallomonas bangladeshica (E. Takah. et T. Hayak.) Siver et A. P. Wolfe was at the base of the first clade that included taxa from the sections Planae and Heterospinae, both of which lack a V rib on the shield of the scales. Our results indicated that the sections Planae and Heterospinae should be combined. The second clade, with Mallomonas insignis Penard and Mallomonas punctifera Korshikov at the base, contained taxa from the sections Mallomonas, Striatae, Akrokomae, Annulatae, Torquatae, Punctiferae, and Insignes, all of which have V ribs or well‐developed marginal ribs on the scales. Sister relationships between Mallomonas and Striatae were strongly supported, but interrelations among the remaining sections were not resolved, probably due to inclusion of too few species. Our results suggest that the current classification of the genus Mallomonas at the section level will require some revision. Additional species will need to be added in future analyses.     

Studies on generaMallomonas andSynura,and other plankton in freshwater with the electron microscope

A new genusSpiniferomonas of the Synuraceae was established withSpiniferomonas bourrellii as the type species. The cells ofSpiniferomonas are solitary, freeswimming, biflagellated, and covered with siliceous scales and spines. The genus shows a similarity to theChrysosphaerella (Synuraceae) in the structure of scales and spines. In addition to the type species, six species were also described as the new taxa of this genus. They were named asS. abei, S. bilacunosa, S. trioralis, S. crucigera, S. conica, andS. alata, respectively. All the specimens were collected from ponds and lakes in Japan.S. trioralis was also collected from the Republic of South Africa. Dedicated to Professor Dr. NoboruAbe in celebration of his sixty-fifth birthday.     

Comparing Morphological and Molecular Estimates of Species Diversity in the Freshwater Genus Synura (Stramenopiles): A Model for Understanding Diversity of Eukaryotic Microorganisms

We performed a comparison of molecular and morphological diversity in a freshwater colonial genus Synura (Chrysophyceae, Stramenopiles), using the island of Newfoundland (Canada) as a case study. We examined the morphological species diversity in collections from 79 localities, and compared these findings to diversity based on molecular characters for 150 strains isolated from the same sites. Of 27 species or species-level lineages identified, only one third was recorded by both molecular and morphological techniques, showing both approaches are complementary in estimating species diversity within this genus. Eight taxa, each representing young evolutionary lineages, were recovered only by sequencing of isolated colonies, whereas ten species were recovered only microscopically. Our complex investigation, involving both morphological and molecular examinations, indicates that our knowledge of Synura diversity is still poor, limited only to a few well-studied areas. We revealed considerable cryptic diversity within the core S. petersenii and S. leptorrhabda lineages. We further resolved the phylogenetic position of two previously described taxa, S. kristiansenii and S. petersenii f. praefracta, propose species-level status for S. petersenii f. praefracta, and describe three new species, S. vinlandica, S. fluviatilis, and S. cornuta. Our findings add to the growing body of literature detailing distribution patterns observed in the genus, ranging from cosmopolitan species, to highly restricted taxa, to species such as S. hibernica found along coastal regions on multiple continents. Finally, our study illustrates the usefulness of combining detailed morphological information with gene sequence data to examine species diversity within chrysophyte algae.     

Dispersal and biogeography of silica-scaled chrysophytes

The silica-scaled chrysophytes—here mainly represented by the freshwater genera Mallomonas and Synura—have special problems in dispersal from one habitat to another because they cannot tolerate desiccation. Their dispersal is limited by the fragile construction and aquatic habit. Dispersal from one water body to another involves dangerous changes of the environment, and the ability to avoid desiccation during transport is crucial. So, air-borne and ectozoic dispersal by birds or mammals can only work at short distances. This danger may be avoided by endozoic dispersal of thick-walled cysts; as far as they can tolerate the digestion fluids in the intestine. In spite of these difficulties, Chrysophytes have been dispersed worldwide, but they display various distinct distribution patterns, e.g., cosmopolitan, arctic-northern temperate, bipolar, and tropical. Quite a large proportion may be considered endemic, occurring only within a restricted area. Even if the exact dispersal methods are elusive, the distribution of chrysophytes around the world proves their ability for dispersal. On the other hand, the different degree of distribution shows the varying success of the individual species. The distribution of a species at a given time depends on several factors: dispersal capacity—available vectors—suitable available habitats—and most important: sufficient time for dispersal. It is remarkable that the chrysophytes—in spite of their fragile cell construction and apparently low dispersal capacity—show distribution types comparable to those found in, e.g., blue–greens and desmids, whose cell construction appears much better adapted for dispersal. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner     

Morphological evolution of silica scales in the freshwater genus Synura (Stramenopiles)

A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus, Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extant Synura species using a robust molecular analysis that included six genes, coupled with morphological characterization of the species‐specific scales. The analysis was further enriched with addition of morphological information from fossil specimens and by including the unique modern species, Synura punctulosa. We inferred the phylogenetic position of the morphologically unique S. punctulosa, to be an ancient Synura lineage related to S. splendida in the section Curtispinae. Some morphological traits, including development of a keel or a labyrinth ribbing pattern on the scale, appeared once in evolution, whereas other structures, such as a hexagonal meshwork pattern, originated independently several times over geologic time. We further uncovered numerous construction principles governing scale morphology and evolution, as follows: (i) scale roundness and pore diameter decreased during evolution; (ii) elongated scales became strengthened by a higher number of struts or ribs; (iii) as a consequence of scale biogenesis, scales with spines possessed smaller basal holes than scales with a keel and; and (iv) the keel area was proportional to scale area, indicating its potential value in strengthening the scale against breakage.     

Studies on chrysophyceae from some ponds and lakes in Alaska vi occurrence of synura species

Summary The Synura species found in samples from a variety of freshwater habitats in Alaska are identified by electron microscope studies of their scales. Synura petersenii f. macracantha Petersen & Hansen and Synura spinosa f. curtispina Petersen & Hansen are raised to specific rank. Synura petersenii f. praefracta n. f., Synura curtispina f. reticulata n. f., and Synura echinulata f. leptorrhabda n. f. are described. Electron micrographs of some scales belonging to undesignated formae are given.Some remarks on the ecology of the Synura species are given.

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Zusammenfassung Synura Arten, die in Proben aus verschiedenen Süßwasser-Lokali-täten in Alaska gefunden werden sind, werden durch elektronenmikroskopische Untersuchungen ihrer Schuppen beschrieben. Zwei Formen, Synura petersenii f. macracantha Petersen & Hansen und Synura petersenii f. curtispina Petersen & Hansen, werden zur Rangstufe der Arten erhoben. Zwei neue Formen, Synura petersenii f. praefracta and Synura curtispina f. reticulata, werden beschrieben.Elektronen-mikroscopische Abbildungen einiger Schuppen, die von unbeschriebenen Formen herrühren, werden gegeben.Einige Anmerkungen über die Ökologie der Synura-Arten werden gemacht.

     

Production of the taste/odor-causing compound,trans-2,cis-6-nonadienal,within the Synurophyceae

Although several species of the Synurophyceae have been associated with taste and odor problems in potable water supplies, electron microscopic-based field studies linked problematic blooms only toSynura petersenii Korshikov. Eventually, the organic compoundtrans-2,cis-6-nonadienal was implicated to cause the associated cucumberlike odors. The objective of this study was to survey unialgal cultures of various Synurophycean species for the occurrence oftrans-2,cis-6-nonadienal. The compound was detected throughout a 24-day growth assay with aS. petersenii isolate, but was not detected in an identical assay withSynura sphagnicola (Korshikov) Korshikov. In separate 24-day cultures,trans-2,cis-6-nonadienal was detected in two isolates from theS. petersenii species complex, but was not detected in isolates of twoMallomonas or fourSynura taxa not from theS. petersenii complex. These results support the hypothesis that production oftrans-2,cis-6-nonadienal is unique to taxa within theS. petersenii complex. When contrast-enhancing optics and specific specimen preparation techniques are employed, light microscopy can be used to distinguish taxa in theS. petersenii complex from all other Synurophycean taxa. These methods are suggested as an efficient way to monitortrans-2,cis-6-nonadienal-producing taxa in potable water supplies.Author for correspondence     

No more lake balls (<Emphasis Type="Italic">Aegagropila linnaei</Emphasis> Kützing,Cladophorophyceae, Chlorophyta) in The Netherlands?

Aegagropila linnaei, a freshwater green macroalga, had been abundant in several locations in The Netherlands before the 1960s. Both the ‘lake ball’ form of this alga and dense unattached mats floating over the sediment have been described from these locations. After 1967, this species has not been recorded anymore from The Netherlands. In 2007, several historical collection sites were surveyed for extant populations of A. linnaei. All habitats have changed drastically during the last 50 years and were affected severely by eutrophication. Populations of A. linnaei seem to have become extinct in all but one location (Boven Wijde, province Overijssel), where we found very small amounts of attached filaments. The attached form had not been reported previously from The Netherlands. Environmental conditions do not seem suitable anymore to maintain extensive unattached growth forms including the enigmatic lake balls, and the species must be regarded as threatened in The Netherlands and we propose to include A. linnaei in a national red list. The decline of populations elsewhere is reviewed and discussed in this paper. In addition to morphological identification of the attached filaments, partial sequences of the nuclear large subunit rDNA were generated and compared with different growth forms and habitats from several other locations outside The Netherlands. The sequences confirm the identity of the Dutch material and indicate very little divergence both between populations in different locations and between different growth forms.     

Mallomonas alphaphora (Chrysophyceae), a new species from Western Australia

A new species ofMallomonas, M. alphaphora (Chrysophyceae), was found in freshwater ponds in the Perth region, Western Australia. It is distinguished from other species ofMallomonas by its very distinctive scale and bristle morphology and is placed in a new section,Alphaphorae, of the genusMallomonas. Dedicated to Prof. DrL. Geitler on the occasion of the 90th anniversary of his birthday.