David R. A. Hill

Cryptomonad nuclear and nucleomorph 18S rRNA phylogeny

Nuclear and nucleomorph 18S ribosomal RNA genes from six cryptomonads were amplified by the polymerase chain reaction and sequenced. Phylogenetic trees were constructed by distance, parsimony, and maximum likelihood methods for all available cryptomonad nuclear and nucleomorph 18S rRNA sequences. Nuclear and nucleomorph trees are largely congruent and clearly disprove the idea of polyphyletic origins for cryptomonad chloroplasts. Both show the leucoplast-containing Chilomonas as the sister to all photosynthetic cryptomonads. Using 11 cryptomonad nucleomorph sequences gives more convincing evidence than before that cryptomonad nucleomorphs originated from a red alga and are not specifically related to Chlorarachnion nucleomorphs. Both trees show as a clade the genera with nucleomorphs embedded in a chloroplast-envelope invagination into the pyrenoid (Storeatula, Rhinomonas, Rhodomonas). This monophyly of embedded nucleomorphs supports the recent creation of the order Pyrenomonadales for such cryptomonads. ...

Goniomonas: rRNA sequences indicate that this phagotrophic flagellate is a close relative of the host component of cryptomonads

The nucleotide sequence of the polymerase chain reaction (PCR)-amplified small subunit ribosomal RNA gene of Goniomonas truncata was determined. Addition of the Goniomonas sequence to the eukaryotic phylogenetic tree revealed this heterotrophic flagellate to be the sister taxon of photosynthetic cryptomonads. The molecular phylogeny supports morphological data suggesting that Goniomonas diverted from the cryptomonad lineage prior to their acquisition of a plastid through endosymbiosis of a eukaryote. Goniomonas, which is phagotrophic, may thus represent an extant relative of the host component of cryptomonad algae.

A Taxonomic Survey of Cyst-producing Dinoflagellates from Recent Sediments of Victorian Coastal Waters, Australia

Forty-two types of cysts representing fourteen dinoflagellate genera were identified in Recent coastal sediments from Victoria, Australia. The most common were those of Scrippsiella trochoidea, Gonyaulax spinifera, Protoperidinium subinerme, Zygabikodinium lenticulatum, Polykrikos schwartzii and Protoperidinium punctulatum. Cysts belonging to the toxic dinoflagellate Gymnodinium catenation were identified in several sediment samples, constituting the first records of G. catenatüm for both Victoria and the Australian mainland, and introducing a new aspect to the regional distribution of G. catenatum. As a result of cyst incubation experiments, twenty-three cyst-theca relationships are described of which five were previously unknown (Protoperidinium cf. achromaticum, P. obtusum, Lebouraia minuta, Gyrodinium undulans and Gyrodinium impudicum).

CRYPTOMONAD EVOLUTION: NUCLEAR 18S rDNA PHYLOGENY VERSUS CELL MORPHOLOGY AND PIGMENTATION1

A nuclear18S rDNA phylogeny for cryptomonad algae is presented, including 11 species yet to be investigated by molecular means. The phylogenetic positions of the cryptomonad genera Campylomonas and Plagioselmis are assessed for the first time. Campylomonas groups most closely with morphologically similar species with the same accessory pigment from the genus Cryptomonas. Plagioselmis groups with the genera Teleaulax and Geminigera forming a clade whose members are united by unusual thylakoid arrangement. Nuclear 18S rDNA phylogeny divides cryptomonads into seven major lineages, two of which consist of the monospecific genera Proteomonas and Falcomonas. Analysis of nuclear18S rDNA sequence supports suggestions that a Falcomonas‐like cryptomonad gave rise to all other blue‐green cryptomonads. New sequence from the plastid‐lacking cryptomonad genus Goniomonas is also included, and the order of divergence of the major cryptomonad lineages is discussed. The morphology, number, and pigmentation of the cryptomonad plastidial complex are congruent with nuclear 18S rDNA phylogenies. Host cell features, such as periplast type, furrow/gullet system, and cell shape, can be more variable and may be markedly different in species that are closely related by nuclear 18S rDNA phylogeny. Conversely, some species that are not closely related by molecular phylogeny may display a very similar, possibly primitive, periplast and furrow morphology.

Lipid profile remodeling in response to nitrogen deprivation in the microalgae Chlorella sp. (Trebouxiophyceae) and Nannochloropsis sp. (Eustigmatophyceae).

Many species of microalgae produce greatly enhanced amounts of triacylglycerides (TAGs), the key product for biodiesel production, in response to specific environmental stresses. Improvement of TAG production by microalgae through optimization of growth regimes is of great interest. This relies on understanding microalgal lipid metabolism in relation to stress response in particular the deprivation of nutrients that can induce enhanced TAG synthesis. In this study, a detailed investigation of changes in lipid composition in Chlorella sp. and Nannochloropsis sp. in response to nitrogen deprivation (N-deprivation) was performed to provide novel mechanistic insights into the lipidome during stress. As expected, an increase in TAGs and an overall decrease in polar lipids were observed. However, while most membrane lipid classes (phosphoglycerolipids and glycolipids) were found to decrease, the non-nitrogen containing phosphatidylglycerol levels increased considerably in both algae from initially low levels. Of particular significance, it was observed that the acyl composition of TAGs in Nannochloropsis sp. remain relatively constant, whereas Chlorella sp. showed greater variability following N-deprivation. In both algae the overall fatty acid profiles of the polar lipid classes were largely unaffected by N-deprivation, suggesting a specific FA profile for each compartment is maintained to enable continued function despite considerable reductions in the amount of these lipids. The changes observed in the overall fatty acid profile were due primarily to the decrease in proportion of polar lipids to TAGs. This study provides the most detailed lipidomic information on two different microalgae with utility in biodiesel production and nutraceutical industries and proposes the mechanisms for this rearrangement. This research also highlights the usefulness of the latest MS-based approaches for microalgae lipid research.

A Quantitative Analysis of Microalgal Lipids for Optimization of Biodiesel and Omega-3 Production

The lipid characteristics of microalgae are known to differ between species and change with growth conditions. This work provides a methodology for lipid characterization that enables selection of the optimal strain, cultivation conditions, and processing pathway for commercial biodiesel production from microalgae. Two different microalgal species, Nannochloropsis sp. and Chlorella sp., were cultivated under both nitrogen replete and nitrogen depleted conditions. Lipids were extracted and fractionated into three major classes and quantified gravimetrically. The fatty acid profile of each fraction was analyzed using GC–MS. The resulting quantitative lipid data for each of the cultures is discussed in the context of biodiesel and omega‐3 production. This approach illustrates how the growth conditions greatly affect the distribution of fatty acid present in the major lipid classes and therefore the suitability of the lipid extracts for biodiesel and other secondary products. Biotechnol. Bioeng. 2013; 110: 2096–2104.

Quantitative evaluation of the ease of rupture of industrially promising microalgae by high pressure homogenization.

The susceptibility to rupture of the microalgae Nannochloropsis sp., Chlorella sp. and Tetraselmis suecica by high pressure homogenization was compared quantitatively to the yeast Saccharomyces cerevisiae. Methods for quantifying cell rupture were investigated including cell counting, turbidity, metabolite release and particle sizing. Cell counting was the only reliable method for quantitative comparisons of all microalgae, with turbidity complicated by agglomeration of cell debris for T. suecica, and measurement of metabolite release affected by degradation occurring for all microalgae after significant rupture. The rupture of all microalgae followed exponential decay as a function of number of passes. The pressure required to achieve rupture of 50% of the cells per pass was determined to be 170, 1070, 1380, and ca. 2000 bar for Tetraselmis sp., Chlorella sp., S. cerevisiae, and Nannochloropsis sp., respectively. These results extend the criteria for selecting microalgae for industrial applications beyond consideration of growth and compositional attributes.

CHROOMONAS AND OTHER BLUE-GREEN CRYPTOMONADS1

Examination of four selected Chroomonas species indicates significant structural diversity within the genus. The concept of Chroomonas is reviewed, and new observations are presented on C. collegionis sp. nov. and C. coerulea (Geitler) Skuja. Examination of two other species, Chroomonas caudata Geitler and Chroomonas daucoides Conrad et Kufferath, forms the basis for the description of two new genera, Komma and Falcomonas. The generic taxonomy is based on the nature of the furrow‐gullet system, periplast structure, and features of the plastidial complex. Certain nomenclatural treatments were required: Cyanomonas americana (Davis) Oltmanns is transferred to Chroomonas, C. rosenbergiae Huber‐Pestalozzi is relegated to synonymy with C. coerulea (Geitler) Skuja, and the descriptions of Butchers species C. mesostigmatica sp. nov. and C. collegionis sp. nov. are completed.

CELLULAR MOVEMENT IN THE CENTRIC DIATOM ODONTELLA SINENIS1

Cultured, actively growing cells of Odentella sinensis secrete mucilage, forming gelatinous masses; the mucilage can be visualised with Alcian Blue. When examined live with the light microscope, many cells exhibited continuous small shuffing and rocking movements that could last for long periods (30‐40 min); the cells, however, were not translocated and remained relatively fixed in position with respect to their neighbours.

ACTIVE GLIDING MOTILITY IN AN ARAPHID MARINE DIATOM, ARDISSONEA (FORMERLY SYNEDRA) CRYSTALLINA1

Active gliding movement over long distances was observed and filmed in the marine pennate diatom Ardissonea (Synedra) crystallina (Agardh) Kütz. Typical speeds measured ca. 1–2 μm‐s−1. Motion wax often smooth and steady; however, discontinuous jerky motions and rolling movements were common. Motion, was associated with secretion of twin or, less commonly, single straight trails of mucilage from one end of the cell. In a few instances, reversal in direction was related to cessation of mucilage secretion at one end and commencement at the other. Temporary cessation of movement due to an obstruction was accompanied by a build‐up of mucilage at one end of the cell. Mucilage was apparently secreted at two specific sites at each end of the cell and was stained by alcian blue.