Yvonne Němcová

Ammonia-free method for preparation of CdS nanocrystalline films by chemical bath deposition technique

The preparation of thin films of CdS by chemical bath deposition is mostly based on the utilisation of ammonia as a complexing agent for cadmium ions. Here we report on a new method based on potassium nitrilotriacetate that eliminates the problems of ammonia volatility and toxicity. We prepared high quality films of closely packed nanocrystals with a thickness of up to 300 nm. The radius of the nanocrystals can be tuned from 2.6 to more than 10 nm by post-preparation heat treatment of the as-prepared films.

Xylochloris irregularis gen. et sp. nov. (Trebouxiophyceae, Chlorophyta), a novel subaerial coccoid green alga

Neustupa J., Eliáš M., Škaloud P., Němcová Y. and Šejnohová L. 2011. Xylochloris irregularis gen. et sp. nov. (Trebouxiophyceae, Chlorophyta), a novel subaerial coccoid green alga. Phycologia 50: 57–66. DOI: 10.2216/08-64.1 The phylogenetic diversity of subaerial coccoid green algae remains still poorly explored. We characterised in detail two unicellular green algae found on tropical trees in Singapore. Light microscopy revealed morphological identity of these two strains. Depending on the age of cultures, the cells were spherical to cylindrical, and ranged in size from 13.5 to 20.5 µm. Each cell contained a pyrenoid-bearing parietal chloroplast that was typically somewhat detached from the plasma membrane on its parietal side. The cells reproduced by 4–16 globular autospores. The 18S rRNA gene sequences of the two strains differed by only a single nucleotide, indicating probable conspecificity. Because the strains were morphologically most comparable to species of the genus Parietochloris, we determined the 18S rRNA gene sequences from authentic strains of three Parietochloris species (P. alveolaris, P. cohaerens and P. ovoidea) for comparison. Molecular phylogenetic analyses placed all five examined strains into the class Trebouxiophyceae. The two novel tropical strains were found to be an independent lineage without an obvious sister group. The type species of the genus Parietochloris, P. alveolaris formed a monophyletic lineage with Parietochloris pseudalveolaris. Finally, P. cohaerens and P. ovoidea fell into another independent clade that also contained Lobosphaera tirolensis, L. incisa and Myrmecia bisecta, indicating that the genus Parietochloris as previously defined is polyphyletic. Based on our morphological and molecular phylogenetic data, we describe the two novel tropical strains as representatives of a new trebouxiophycean genus and species, Xylochloris irregularis gen. et sp. nov.

Nanocrystalline titanium dioxide films: Influence of ambient conditions on surface- and volume-related photoluminescence

We report on systematic study of photoluminescence properties of nanocrystalline titanium dioxide films consisting of predominantly anatase nanoparticles with diameters larger than 13 nm. We measured photoluminescence under two selected excitation wavelengths (325 nm/442 nm, i.e., above/below band gap excitation), under different values of ambient air pressure (5–105u2002Pa), and in the temperature interval 10–300 K. On basis of our results, we are able to distinguish two different processes leading to photoluminescence: the exciton recombination and the recombination of carriers in the energy states related to the surface of nanocrystals. We propose microscopic models describing well the effects of temperature and ambient conditions on photoluminescence of nanocrystalline titanium dioxide films.

JENUFA GEN. NOV.: A NEW GENUS OF COCCOID GREEN ALGAE (CHLOROPHYCEAE, INCERTAE SEDIS) PREVIOUSLY RECORDED BY ENVIRONMENTAL SEQUENCING(1).

The diversity of eukaryotic microorganisms is far from fully described, as indicated by the vast number of unassigned genotypes retrieved by environmental sequencing or metagenomics. We isolated several strains of unicellular green algae from algal biofilms growing on tree bark in a Southeast Asian tropical rainforest and determined them to be relatives of an unidentified lineage of environmental 18S rDNA sequences, thus uncovering its cellular identity. Light, confocal, and electron microscope observations and sequencing the 18S rRNA gene revealed that the strains represent two different species within an apparently new genus, described here as Jenufa gen. nov. Both species formed minute coccoid cells with an irregular globular outline, a smooth cell wall, and a single parietal chloroplast without a pyrenoid. The two species, described herein as J. perforata and J. minuta, differed in chloroplast morphology and cell wall structure. Phylogenetic analyses of 18S rRNA gene sequences showed a firm relationship between the two species and placed the Jenufa lineage in an unresolved position within the CS clade (Chlamydomonadales + Sphaeropleales) of the class Chlorophyceae, although possible affinities to the genus Golenkinia were suggested both by maximum‐likelihood (ML) and Bayesian methods. Furthermore, two almost identical environmental 18S rDNA sequences from an endolithic microbial community occurring in dolomite rock in the central Alps turned out to be specifically related to, yet apparently distinct from, the sequence of J.u2003minuta, indicating the existence of an undescribed Jenufa species occurring in the temperate zone.

Hylodesmus singaporensis gen. et sp. nov., a new autosporic subaerial green alga (Scenedesmaceae, Chlorophyta) from Singapore.

The algal flora of subaerial habitats in the tropics remains largely unexplored, despite the fact that it potentially encompasses a wealth of new evolutionary diversity. Here we present a detailed morphological and molecular characterization of an autosporic coccoid green alga isolated from decaying wood in a natural forest in Singapore. Depending on culture conditions, this alga formed globular to irregularly oval solitary cells. Autosporulation was the only mode of reproduction observed. The cell periphery was filled with numerous vacuoles, and a single parietal chloroplast contained a conspicuous pyrenoid surrounded by a bipartite starch envelope. The cell wall was composed of a thick inner layer and a thin trilaminar outer layer, and the cell surface was ornamented with a few delicate ribs. Phylogenetic analyses of 18S rRNA gene sequences placed our strain in the family Scenedesmaceae (Sphaeropleales, Chlorophyceae) as a strongly supported sister branch of the genus Desmodesmus. Analyses of an alternative phylogenetic marker widely used for the Scenedesmaceae, the ITS2 region, confirmed that the strain is distinct from any scenedesmacean alga sequenced to date, but is related to the genus Desmodesmus, despite lacking the defining phenotypic features of Desmodesmus (cell wall with four sporopolleninic layers ornamented with peculiar submicroscopic structures). Collectively, our results establish that we identified a novel, previously undocumented, evolutionary lineage of scenedesmacean algae necessitating its description as a new species in a new genus. We propose it be named Hylodesmus singaporensis gen. et sp. nov. A cryopreserved holotype specimen has been deposited into the Culture Collection of Algae of Charles University in Prague, Czech Republic (CAUP) as CAUP C-H8001.

Photoluminescence of nanocrystalline titanium dioxide films loaded with silver nanoparticles

We report on a systematic study of the photoluminescence properties of nanocrystalline titanium dioxide films loaded with silver nanoparticles under various ambient conditions: in the temperature interval of 10 to 300 K, under different values of ambient air pressure (5 to 105 Pa), and under visible light irradiation that causes the photochromic transformation of the film. Our results enable us to follow the electron transfer from titanium dioxide into silver nanoparticles and to observe the oxidation of silver nanoparticles during the photochromic transformation. We propose a microscopic model explaining the behavior of extinction and photoluminescence of the Ag–TiO2 film under different values of ambient air pressure.

Parachloroidium gen. nov. (Trebouxiophyceae, Chlorophyta), a novel genus of coccoid green algae from subaerial corticolous biofilms

Neustupa J., Němcová Y., Veselá J., Steinová J. and Škaloud P. 2013. Parachloroidium gen. nov. (Trebouxiophyceae, Chlorophyta), a novel genus of coccoid green algae from subaerial corticolous biofilms. Phycologia 52: 411–421. DOI: 10.2216/13–142.1 The Watanabea clade of the Trebouxiophyceae included mostly unicellular coccoid microalgae that thrived in various terrestrial microhabitats. The diversity of these morphologically uniform microalgae was little known, and several new genus-level lineages had recently been described on the basis of molecular data. In this study, we provided a taxonomic description of a new trebouxiophycean genus, Parachloroidium, found in the Mediterranean in corticolous phototrophic biofilms. Their simple chlorelloid morphology did not unambiguously distinguish the Parachloroidium strains from other similar green algae. However, ultrastructural characteristics and molecular phylogenetic analyses based on the 18S ribosomal (r)DNA, internal transcribed spacer region (ITS) and the chloroplast ribulose-bisphosphate carboxylase gene sequences provided a basis for the discrimination of Parachloroidium from related genera of the Watanabea clade. The four strains investigated formed two species, P. laureanum and P. lobatum, which differed in plastid morphology and in ITS and 18S rDNA sequences. All four strains were characterized by globular or ellipsoidal cell shapes, single parietal plastids and asexual reproduction by autospores. Their plastids lacked typical pyrenoids; however, plastids included peculiar thylakoid-free regions of irregular shape. On the basis of accumulating molecular data, we concluded that the Watanabea clade was a diverse phylogenetic lineage within the subaerial chlorelloid green algae.

Morphological delineation and distribution patterns of four newly described species within the Synura petersenii species complex (Chrysophyceae, Stramenopiles)

The Synura petersenii species complex represents a common, cosmopolitan and highly diverse taxon of autotrophic freshwater flagellates. In this paper, we describe and characterize four new species (S. borealis, S. heteropora, S. hibernica and S. laticarina) that have been identified during our extensive sampling of freshwater habitats in 15 European countries. Morphometric analyses of siliceous scales led to the significant phenotypic differentiation of all four newly described species, and their separation from other related species of the S. petersenii complex. Two of these newly described species (S. hibernica and S. borealis) can be clearly distinguished by characteristic large colonies consisting of elongated, lanceolate-shaped cells. Development of strongly elongated, narrow cells in S. hibernica could be explained by the adaptation of this species to oligotrophic conditions. Though morphologically distinct, S. borealis possesses an exceptionally high degree of genetic diversity, possibly indicating recent speciation and evolutionary diversification within this taxon. Three of the four newly described species exhibit restricted biogeographic distribution. The evolutionarily related S. borealis and S. laticarina occur only in Northern Europe, and seem to be adapted to colder areas. The most remarkable distribution pattern was observed for S. hibernica, which has a geographic distribution that is restricted to western Ireland.

Chloropyrula uraliensis gen. et sp. nov. (Trebouxiophyceae, Chlorophyta), a new green coccoid alga with a unique ultrastructure, isolated from soil in South Urals

Soil hosts diverse communities of photosynthetic eukaryotes (algae) that have not yet been fully explored. Here we describe an interesting coccoid green alga isolated from a soil sample from a forest‐steppe in South Urals (Bashkortostan, Russia) that, based on a phylogenetic analysis of 18S rRNA gene sequence, appears to represent a new phylogenetic lineage related to the genus Leptosira within the class Trebouxiophyceae. This new alga is characterized by uninucleate cells with a shape ranging from spherical to ellipsoid or egg‐like, occurring solitary or more often grouped in irregular masses or colonies. Remarkably, cells with a characteristic pyriform shape are encountered in cultures grown on a solid medium. The cells harbour a single pyrenoid‐lacking parietal chloroplast with the margin undulated or forming finger‐like projections; in mature cells the chloroplast becomes divided by deep incisions into more or less separate lobes. Transmission electron microscopy of vegetative cells revealed an unprecedented structure in the form of a cluster of microfibrils located in the cytoplasm near the plasma membrane, often appressed to the chloroplast. Reproduction takes place via autospores or biflagellated zoospores. The unique suite of characters of our isolate distinguishes it from previously described coccoid green algae and suggests that it should be classified as a new species in a new genus; we propose it be named Chloropyrula uraliensis.

Synura obesa sp. nov. (Synurophyceae) and other silica-scaled chrysophytes from Abisko (Swedish Lapland)

Ten taxa of silica-scaled chrysophytes (Synurophyceae and Chrysophyceae) were found during an investigation of mires and peat bogs in the Abisko region (Swedish Lapland). The chrysophyte flora consisted mainly of acidophilic (Synura echinulata, S. sphagnicola, Chrysosphaerella longispina) or pH indifferent widely distributed taxa. Together with frequently reported taxa the rare Synura petersenii f. bjoerkii and a new species of Synura, S. obesa were found. Mallomonas corcontica was reported for the first time from Sweden. The occurrence of the species is discussed in relation to some environmental factors (particularly pH).