Cyclotella Nana Research Articles

Growth, survival and fatty acid profile of hard clam, Mercenaria mercenaria, juveniles fed live microalgae diets

AbstractChoice of microalgae diet affects production outcomes in bivalve hatcheries. This study aimed to identify an optimal microalgae diet to improve hard clam, Mercenaria mercenaria, juvenile production. Four microalgae species (Tisochrysis lutea, Pavlova lutheri, Chaetoceros gracilis and Cyclotella nana) in six dietary combinations were fed for 6 weeks; then, growth, survival and fatty acid profiles of juveniles were evaluated. The highest numerical growth and survival of juveniles were attained by feeding a tetra‐species microalgae diet, but no statistical difference was found by feeding bi‐ or tri‐species diets that consisted of a mix of flagellate and diatom microalgae. Significant differences in fatty acid profiles were found among clams fed different microalgae diets. A contrasting polyunsaturated fatty acid (PUFA) profile was found in juveniles fed flagellate‐ or diatom‐only diets. Clams fed flagellate‐only diets contained a higher percentage of docosahexaenoic acid (DHA) but a lower percentage of (n‐6) PUFAs, whereas those fed diatom‐only diets had a higher percentage of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) but a lower percentage of DHA. In contrast, the percentage of EPA, DHA and ARA was neither very high nor very low in juveniles fed the tetra‐species diet. The complementary nutritional profile of the tetra‐species microalgae diet resulted in enhanced production and exhibited a more balanced fatty acid profile in clam tissue. The tetra‐species microalgae diet should be a preferable choice for feeding hard clam juveniles, but the cost of producing multiple microalgae species for hatchery/nursery operations should be taken into consideration as bi‐ and tri‐species diets provided statistically similar growth and survival. Results of this study can be used to improve productivity and profitability in M. mercenaria hatcheries.

Conserved gene order and expanded inverted repeats characterize plastid genomes of Thalassiosirales.

Diatoms are mostly photosynthetic eukaryotes within the heterokont lineage. Variable plastid genome sizes and extensive genome rearrangements have been observed across the diatom phylogeny, but little is known about plastid genome evolution within order- or family-level clades. The Thalassiosirales is one of the more comprehensively studied orders in terms of both genetics and morphology. Seven complete diatom plastid genomes are reported here including four Thalassiosirales: Thalassiosira weissflogii, Roundia cardiophora, Cyclotella sp. WC03_2, Cyclotella sp. L04_2, and three additional non-Thalassiosirales species Chaetoceros simplex, Cerataulina daemon, and Rhizosolenia imbricata. The sizes of the seven genomes vary from 116,459 to 129,498 bp, and their genomes are compact and lack introns. The larger size of the plastid genomes of Thalassiosirales compared to other diatoms is due primarily to expansion of the inverted repeat. Gene content within Thalassiosirales is more conserved compared to other diatom lineages. Gene order within Thalassiosirales is highly conserved except for the extensive genome rearrangement in Thalassiosira oceanica. Cyclotella nana, Thalassiosira weissflogii and Roundia cardiophora share an identical gene order, which is inferred to be the ancestral order for the Thalassiosirales, differing from that of the other two Cyclotella species by a single inversion. The genes ilvB and ilvH are missing in all six diatom plastid genomes except for Cerataulina daemon, suggesting an independent gain of these genes in this species. The acpP1 gene is missing in all Thalassiosirales, suggesting that its loss may be a synapomorphy for the order and this gene may have been functionally transferred to the nucleus. Three genes involved in photosynthesis, psaE, psaI, psaM, are missing in Rhizosolenia imbricata, which represents the first documented instance of the loss of photosynthetic genes in diatom plastid genomes.

Timing marine–freshwater transitions in the diatom order Thalassiosirales

With species found throughout both marine and fresh waters, the diatom order Thalassiosirales is one of the most phylogenetically and ecologically diverse lineages of planktonic diatoms. A clear understanding of the timescale of Thalassiosirales evolution would provide novel insights into the rates and patterns of species diversification associated with major habitat shifts, as well as provide valuable context for understanding the age and evolutionary history of the model species, Cyclotella nana (= Thalassiosira pseudonana). The freshwater fossil record for Thalassiosirales is extensive, well characterized, and generally supportive of a Miocene origin for the major freshwater lineages. The marine record is, by comparison, more sparse and in many cases, unverified. The discovery of freshwater thalassiosiroids in Eocene sediments pushed the freshwater fossil record considerably further back in time, highlighting an apparent gap of some 30 million years. An alternative interpretation is that the Miocene and Eocene reports represent competing hypotheses. In the absence of additional independent and decisive fossil data, I explored the relative plausibility of these two scenarios with Bayesian relaxed molecular clock methods under a range of fossil calibration schemes. Although I found no support for the Eocene fossil dates, the two major freshwater colonization events probably occurred much earlier than previously thought—as early as the Paleocene for Cyclotella, followed by an Eocene origin for the cyclostephanoid lineage. Much of the extant freshwater diversity in both lineages traces back to the Miocene, however, giving the impression of a single Miocene origin. Efforts to infer the timescale of Thalassiosirales evolution more accurately would benefit from a systematic reevaluation of the marine fossil record and formal integration of fossil species into existing phylogenetic hypotheses.

The model marine diatom Thalassiosira pseudonana likely descended from a freshwater ancestor in the genus Cyclotella

BackgroundPublication of the first diatom genome, that of Thalassiosira pseudonana, established it as a model species for experimental and genomic studies of diatoms. Virtually every ensuing study has treated T. pseudonana as a marine diatom, with genomic and experimental data valued for their insights into the ecology and evolution of diatoms in the world's oceans.ResultsThe natural distribution of T. pseudonana spans both marine and fresh waters, and phylogenetic analyses of morphological and molecular datasets show that, 1) T. pseudonana marks an early divergence in a major freshwater radiation by diatoms, and 2) as a species, T. pseudonana is likely ancestrally freshwater. Marine strains therefore represent recent recolonizations of higher salinity habitats. In addition, the combination of a relatively nondescript form and a convoluted taxonomic history has introduced some confusion about the identity of T. pseudonana and, by extension, its phylogeny and ecology. We resolve these issues and use phylogenetic criteria to show that T. pseudonana is more appropriately classified by its original name, Cyclotella nana. Cyclotella contains a mix of marine and freshwater species and so more accurately conveys the complexities of the phylogenetic and natural histories of T. pseudonana.ConclusionsThe multitude of physical barriers that likely must be overcome for diatoms to successfully colonize freshwaters suggests that the physiological traits of T. pseudonana, and the genes underlying those traits, might differ from those of strictly marine diatoms. The freshwater ancestry of T. pseudonana might therefore confound generalizations about the physiological and metabolic properties of marine diatoms. The freshwater component of T. pseudonana's history merits careful consideration in the interpretation of experimental data collected for this important model species.

Relationships between phytoplankton occurrence and salinity or water temperature in brackish Lake Nakanoumi, 1979-1986.

The relationships between the occurrence of phytoplankton and salinity or water temperature have been investigated for 8 years from 1979 to 1986 in brackish Lake Nakanoumi. Fourteen species such as Skeletonema costatum, Prorocentrum minimum and Cyclotella nana were dominant in this lake. Five among the 14 species bloomed in conditions of water temperature less than optimal for their growth, whereas every species bloomed in optimum salinity conditions. This fact indicates that the occurrence of dominant species in the lake is more strongly controlled by salinity than water temperature.The result of comparison of weighted mean value of water temperature and salinity for the two periods of 1974-1978 and 1979-1986 also indicated the greater importance of salinity than water temperature.

Occurrence of phosphatidylsulfocholine, the sulfonium analog of phosphatidylcholine in some diatoms and algae

A survey of seven species of diatoms, one Euglena sp. and one dinoflagellate sp. for the presence of phosphatidylsulfocholine (PSC), the sulfonium analog of phosphatidylcholine (PC), was carried out using 1H-NMR spectroscopy and ammonia desorption chemical ionization mass spectrometry. PSC alone was found only in a non-photosynthetic diatom, Nitzschia alba. PSC, together with PC, was found in four of the diatoms ( Nitzschia angularis, Cylindrotheca fusiformis, Phaeodactylum tricornutum and Navicula pelliculosa) in proportions of 6–24% of the total PC + PSC fraction, but little or no PSC (less than 2%) was detected in the remaining two ( Cyclotella nana and Navicula incerta). Little or no PSC (less than 2%) was detected in a Euglena sp. by 1H-NMR but its presence was confirmed by 35S-labeling. The amount of PSC, if any, in the dinoflagellate ( Amphidinium carterae) was below the level of detection by 1H-NMR.

THE MARINE, PLANKTONIC DIATOMS THALASSIOSIRA OCEANICA SP. NOV. AND T. PARTHENEIA1

ABSTRACTThe diatom clone 13–1 isolated from the Sargasso Sea by Dr. R. R. L. Guillard as Cyclotella nana Hust. or Thalassiosira pseudonana Hasle and Heimdal is described as a separate species, Thalassiosira oceanica sp. nov. An amplified diagnosis of Thalassiosira partheneia Schrader is given, and a comparison of the two species is made based on light and electron microscopy. Similarities are present in the apparent distribution pattern, cell size, and girdle structure. Differences are present in the shape of the areolae of the valvocopula and the copula, in the structure of the vela of these bands, in the texture of the external valve surface, in the morphology of the strutted processes, in the location of the labiate process, in the distance between the marginal strutted processes, and by the presence of a marginal ridge in T. oceanica. Fifteen nanoplanktonic (maximum diameter = 20 UmUm) Thalassiosira species are listed, among them T. oceanica and T. partheneia.

The site of β-chitin fibril formation in centric diatoms. I. Pores and fibril formation

The silica valve structures related to β -chitin fibril formation were investigated in the centric diatom algae Cyclotella cryptica, Cyclotella nana, Cyclotella meneghiniana , and Thalassiosira fluviatilis with transmission and scanning electron microscopy. The results for T. fluviatilis are given in detail: The silica valves are characterized by a marginal ring of up to 86 pores and a central, less regular set of pores. The pores are surrounded by a system of chambers and supporting structures. The β -chitin fibrils originate from these pore apparatuses. All pores may function in fibril formation. Normally one, but sometimes two, fibril is seen to be attached in a pore. Each pore may be the source of numerous, sequentially formed fibrils, as judged from the huge number of chitin fibrils, relative to the number of cells, when the fibrils are continually detached from the cells by aerating the cultures. In the investigated Cyclotella species, the situation is very similar with respect to pores and chitin fibrils, with species-specific variations in the architecture of the pore apparatus and the valves. It is concluded that the pores of the investigated centric diatoms are structures specialized for the formation of β -chitin fibrils.

The site of β-chitin fibril formation in centric diatoms. II. The chitin-forming cytoplasmic structures

β-Chitin fibril formation was investigated in the centric diatoms Cyclotella cryptica, Cyclotella nana, Cyclotella meneghiniana, and Thalassiosira fluviatilis with transmission electron microscopy. The pores in the silica valves from which the fibrils originate were examined in serial sectioning to identify the underlying cytoplasmic structures involved in chitin formation. In all species synthesizing chitin, the fibrils originate from special invaginations of the plasma membrane. These invaginations are conical and bear a special coat on their cytoplasmic face. This coat shows a hexagonal arrangement. It is assumed that this coat plays a role in chitin fibril formation, which seems to be a transmembrane event. Kinetic data on fibril formation and calculations on the package density of synthetase molecules which should be localized in the conical plasma membrane invagination are discussed in relation to the special coat subunits. A relationship between the conical invaginations and a chitosome-like type of vesicles was observed only in Thalassiosira.

Effects of light intensity on photosynthesis and dark respiration in six species of marine phytoplankton

Using an oxygen polarographic electrode, the shapes of photosynthetic curves and the effects of light on dark respiration in 6 species of marine phytoplankton wer examined. The species used were Skeletonema costatum, Ditylum brightwellii, Cyclotella nana (Thalassiosira pseudonana) (all Bacillariophyceae), Dunaliella tertiolecta (Chlorophyceae), Isochrysis galbana (Haptophyceae), and Gonyaulax tamarensis (Dinophyceae). A hysteresis was observed in all species examined with respect to increasing and decreasing light. Compensation light intensities varied by over 4 orders of magnitude, suggesting that the 1% light depth is an ambiguous measure of the euphotic zone. The data suggest that dark respiration accounts for ca. 25% of gross photosynthesis, but is species-dependent. In addition, respiration versus cell size does not describe an inverse exponential function over the size scales examined.

In vivo fluorescence determinations of phytoplankton chlorophyll a

The in vivo fluorescence yield of chlorophyll a in Chlorella pyrenoidosa is shown to vary with the availability of nitrate, trace elements, and with the presence of mercury. The fluorescence yield of Phaeodactylum tricornutum also varies with culture conditions and comparisons of Cyclotella nana and Chaetoceros galvestonensis show a species‐dependent variation. Both types of yield fluctuations are eliminated when photosynthetic electron transport is blocked by adding 3‐(3,4dichlorophenyl)‐1,1‐dimethylurea (DCMU) to phytoplankton: the in vivo fluorescence yield becomes maximal and a constant function of cellular chlorophyll a, regardless of growth conditions or of the species examined. Preliminary observations of samples from the Caribbean Sea also indicate a constant in vivo fluorescence yield in the presence of DCMU.

Effect of germanic acid on developing cell walls of diatoms

The effects of 0.1 and 1.0 germanic acid/silicic acid concentrations on wall development inNitzschia alba, Navicula pelliculosa, Cylindrotheca fusiformis, and Cyclotella nana are described. Valve development and differentiation are interrupted, and sometimes completely blocked. Girdle band formation is also affected.N. alba produces multiple walls (at 0.1 [Ge]/[Si]) and dense cytoplasmic granules (at 1.0 [Ge]/[Si]).

Examination of diatom type material:Nitzschia delicatissimaCleve,Thalassiosira minusculaKrasske, andCyclotella nanaHustedt

Type material of Thalassiosira minuscula Krasske and material identified by the respective authors as Nitzschia delicatissima Cleve and Cyclotella nana Hustedt (= Thalassiosira pseudonana Hasle et Heimdal) have been examined in light and electron microscopes. It is suggested that the slide labelled “Nitzschia delicatissima Helder 7/5–97” is accepted as neotype of the species since the original material must be regarded as lost, and that Thalassiosira pseudonana is identical to the diatom isolated by Guillard as clone 3-H. Nitzschia actydrophila Hasle and Thalassiosira monoporocyclus Hasle are rejected as separate species, the first being conspecific with N. delicatissima and the second with T. minuscula. The question is raised whether more emphasis should be laid on iconotypes of small diatom species identifiable only in the electron microscope than on real individuals.

Experimental culture of the estuarine ectoproct Conopeum tenuissimum from Chesapeake Bay.

1. The pattern and form of colony growth in the ectoproct Conopeum tenuissimum was found to be diet-dependent.2. Poorly nourished colonies were characterized by their straggling shape and low zooid number to generation number ratios. These colonies apparently attempted to maximize substrate covered, facilitating location of a more favorable nutrient regime.3. Well fed colonies were rounded in shape and characterized by high zooid number to generation number ratios. These colonies maximized the number of zooids produced in their already favorable area, creating colony reserves, and preparing for reproduction.4. Initial growth in all colonies was exponential, but after a few days of culture growth, rates varied with food used. The chlorophyte flagellate Dunaliella tertiolecta and the dinoflagellate Gymnodinium simplex were good foods, supporting growth to more than 1,000 zooids and sexual maturation within the 42 day culture period. The chrysophyte flagellate Monochrysis lutheri and Va-12 (an un-named chrysophyte flagellate) proved to be fair foods, supporting moderate growth, but no sexual maturation. The blue-green alga Anacystis marinus, the chlorophyte Nannochloris occulata, and the diatom Cyclotella nana supported little or no growth, while bacterial food did not support growth of Conopeum cultures.5. Combinations of algal food produced good colony growth. A three-species mixture was better than a two-species mixture, suggesting differential yet additive nutritional contributions by each algal species.6. Increased food concentrations supported increased growth only up to a certain concentration. This growth response varied with salinity.

The effect of mass transport on biostimulation of algal growth

A model is proposed to account for mass transport limitation to the uptake of major nutrients. A thin film diffusion resistance layer is hypothesized. In an example using Cyclotella nana (a diatom), diffusion resistance was calculated to result in a maximum decrease of 40% in phosphorus uptake rate. Transport limitation was demonstrated experimentally. The growth of Chlorella pyrenoidosa (a green alga) was found to be stimulated by shaking the cultures. Using similar mathematical techniques, the internal resistance to the uptake of nutrients in algal cell aggregates was also modeled.

L‐THREONINE DEAMINASE IN MARINE PLANKTONIC ALGAE. V. KINETIC EVALUATION OF FEEDBACK EFFECTS FROM STRUCTURAL ANALOGS OF l‐ISOLEUCINE ON THE DEAMINASE ACTIVITY OF SEVEN UNICELLULAR SPECIES AND ELUCIDATION OF THE ALLOSTERIC BASIS FOR ANOMALOUS FEEDBACK CONTROL SHOWN BY A DIATOM AND A CRYPTOMONAD1,2

SUMMARYThe biosynthetic l‐threonine deaminase of 2 cyanophytes, 1 rhodophyte, 2 cryptomonads, and 1 chlorophyte showed sensitive and powerful feedback inhibition from l‐isoleucine, which effect was closely duplicated by its isosteric structural analog l‐O‐methylthreonine. The l‐isoleucine inhibition was maximal in the pH range 7.0–8.5 and was rapidly weakened with more alkaline pH. Glycine, l‐alanine, and d‐isoleucine had no effect, while l‐α‐amino‐n‐butyric acid, l‐norvaline, l‐leucine, and l‐valine caused insensitive partial inhibitions detectable only at high concentration (100‐fold greater than l‐isoleucine). Tests of these analogs at low concentration revealed the specific capacity of l‐valine to invoke sensitive stimulation of enzyme activity from all the algal strains, and this effect was markedly enhanced by decrease in substrate concentration. Valine also counteracted the inhibitory influence of isoleucine. It was concluded from the reaction kinetics observed with these effectors that the algal threonine deaminases conform to Monad's K system of allosteric enzymes. The activity from the cryptomonad Hemiselmis virescens was exceptional in showing 2 closely spaced pH optima, which were related to marked difference in effects from isoleucine and valine at these pH values. It was inferred from various pH‐related tests that this cryptomonad may contain 2 enzymes basically similar in biosynthetic function but differing only in pH optima and sensitivity to feedback regulation.The enzyme of the diatom Cyclotella nana was unique in showing insignificant feedback reaction from l‐isoleucine and its structural analogs, excepting l‐valine, which caused the strongest stimulation among the algae surveyed. It was concluded from the reaction kinetics that this deaminase is also of the biosynthetic type but that its feedback‐inhibition site is modified or unavailable, presumably from having this site already filled by endogenous isoleucine from the diatom.

NITROGEN ASSIMILATION OF AN OCEANIC DIATOM IN NITROGEN‐LIMITED CONTINUOUS CULTURE1

SUMMARYThe oceanic diatomThalassiosira pseudonanaHasle and Heimdal (formerlyCyclotella nana) was grown with 12L:12D illumination cycles in nitrogen‐limited continuous culture with a mixture of ammonium and nitrate as the N source. Measurements included, at 3 different growth rates (degrees of N limitation), cell concentration, cell carbon, nitrogen, and chlorophyllacontents, cell volume, photosynthetic carbon assimilation vs. irradiance, short‐term uptake of ammonium and nitrate vs. their ambient concentrations, andin vitroactivities of the assimilatory enzymes nitrate reductase and glutamic dehydrogenase.The various parameters showed either an increase (patterna) or a decrease (patternb) with increasing N limitation. Those following patternawere nitrate reductase activity and the capacity to assimilate nitrate and ammonium. Those following patternbwere glutamic dehydrogenase activity, photosynthetic rate, nitrogen:carbon and chlorophylla:carbon composition ratios. Results are discussed in terms of the interpretation such measurement for natural phytoplankton and effects of circadian periodicity.

Photorespiration in diatoms. The oxidation of glycolic acid in Thallassiosira pseudonana (Cyclotella nana).

A glycolate dehydrogenase found in the marine diatom Thallassiosira pseudonana differs significantly from that occurring in other algal systems. It is insensitive to cyanide and prefers the l-isomer of lactic acid although the d-isomer is oxidized slowly. Its specific activity is comparatively high; substrate affinity is rather low (glycolate K m 1.6×10-2 and l(+)lactate K m 2.2×10-2); optimal activity occurs at pH 8.7. It appears to be indirectly linked to oxygen via a system of electron carriers; it is insensitive to metal complexing agents but is partially inactivated by sulfhydryl inhibitors. Attempts to identify possible cofactors were unsuccessful.

KINETICS OF SILICON‐LIMITED GROWTH IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA HASLE AND HEIMDAL (=CYCLOTELLA NANA HUSTEDT)1,2

SUMMARYThe half‐saturation constant (K8) for growth and the maximum growth rate (μmax) were determined for 2 clones of Thalassiosira pseudonana (=Cyclotella nana) under conditions in which external silicon concentrations controlled growth. The estuarine clone (3H) had a higher half‐saturation constant and maximum growth rate (K8= 0.98 μM Si; μmax= 3.6 divisions/day) than the clone from the Sargasso Sea (K8= 0.19 μM Si; μmax= 2.1 divisions/day). The K8 values for each clone are such that the silicate levels found at certain times in both the Sargasso Sea and the coastal regions are rate limiting to growth, hence can be of significance to plant production and to species succession. The yield data are consistent with the concept that growth rate and cellular silicon content vary together in silicon‐limited cultures.

Comparison of rates of feeding and biodeposition of the American oyster, Grassostrea virginica Gmelin, fed different species of phytoplankton

The feeding and biodeposition rates of small (2.4 cm) and large (5.2 cm) Crassostrea virginica were differently affected in experiments using flowing systems by moderate (292 μ C/1 sea water) and high (487 μ C/1 sea water) concentrations of the following phytoplankton: the diatoms, Thalassiosira pseudonana (Hasle & Heindal) ( Cyclotella nana), Skeletonema costatum (Greville) Cleve, Nitzschia closterium (Ehrenberg) Wm. Smith, and the green alga, Dunaliella tertiolecta Butcher. The average feeding rate of the oysters on the different phytoplankton was: Dunaliella < Nitzschia < Skeletonema < Thalassiosira. In contrast, oysters fed on Thalassiosira had the lowest rate of biodeposition (1.626 × 10 −3 g ash-free dry wt/g dry flesh wt per day) but oysters cultured on Nitzschia showed the highest rate of biodeposition (2.952 × 10 −3 units). The response of the feeding rate of the two sizes of oysters to food concentration differed according to the algal food source. Oysters fed on Thalassiosira and Skeletonema exhibited a higher feeding rate at a higher food level: in contrast, oysters fed on Nitzschia showed no significant differences and those cultured on Dunaliella a depressed feeding rate at the higher food concentration. We observed no differences in feeding rate between small and large oysters fed on Skeletonema and Dunaliella, but small oysters had a higher feeding rate than large oysters when cultured on Thalassiosira and a lower feeding rate when fed on Niitzschia. The smaller size of Thalassiosira and larger size of Nitzschia might account for these differences in the feeding efficiency of small oysters. The biodeposition rates of both sizes of oysters were also affected by food concentration of the different algae. At the high food concentration with Skeletonema, Nitzschia, and Dunaliella, all oysters showed a marked increase in the rate of biodeposition, but oysters fed on Thalassiosira exhibited no great change. On all species of phytoplankton, the larger oysters produced greater biodeposition than the smaller oysters. These differences in response of feeding and biodeposition rates are important to our knowledge of food chain dynamics and may be used to optimize aquaculture systems.