Diatom Strains Research Articles

A comparative analysis of fatty acid composition and fucoxanthin content in six Phaeodactylum tricornutum strains from diff erent origins

Phaeodactylum tricornutum is a potential livestock for the combined production of eicosapentaenoic acid (EPA) and fucoxanthin. In this study, six marine diatom strains identified as P. tricornutum were cultured and their total lipid, fatty acid composition and major photosynthetic pigments determined. It was found that the cell dry weight concentration and mean growth rate ranged between 0.24–0.36 g/L and 0.31–0.33/d, respectively. Among the strains, SCSIO771 presented the highest total lipid content, followed by SCSIO828, and the prominent fatty acids in all strains were C16:0, C16:1, C18:1, and C20:5 (EPA). Polyunsaturated fatty acids, including C16:2, C18:2, and EPA, comprised a significant proportion of the total fatty acids. EPA was markedly high in all strains, with the highest in SCSIO828 at 25.65% of total fatty acids. Fucoxanthin was the most abundant pigment in all strains, with the highest in SCSIO828 as well, at 5.50 mg/g. The collective results suggested that strain SCSIO828 could be considered a good candidate for the concurrent production of EPA and fucoxanthin.

Light and temperature effects on bioactivity in diatoms.

Isolates of five pelagic North Atlantic marine diatoms (Bacillariophyceae): Attheya longicornis, Chaetoceros socialis, Chaetoceros furcellatus, Skeletonema marinoi and Porosira glacialis were cultivated in large photobioreactors at two light and two temperature regimes to test if this affected bioactivity. We screened for bioactivity in assays representing five different therapeutic areas: diabetes II (PTP1b), cancer (melanoma cells, A2058), anti-oxidants (FRAP), immunomodulation (TNFa) and anti-infection (MRSA, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa). All the diatom strains showed activity in two or more assays. We detected differences in bioactivity both between species and within species cultivated with different light and temperature regimes. Our results demonstrate the potential for a more exhaustive exploitation of diatom metabolites that can be obtained by manipulation of the cultivation conditions.

Detection of domoic acid in Mytilus galloprovincialis and Ostrea edulis linked to the presence of Nitzschia bizertensis in Bizerte Lagoon (SW Mediterranean)

Seasonal variation of DA in bivalves was monitored from August 2008 to March 2009 at a shellfish station in Bizerte Lagoon, one of the most important shellfish areas in Tunisia. At the same time, dynamics of potentially toxic diatoms was studied at six stations in the lagoon. Several diatom strains were isolated, maintained in culture and their identification as well as the toxicity was examined.During the study period, domoic acid (DA) was detected in Tunisia, in both mussels (Mytilus galloprovincialis: 0.13–0.86 μg DA g−1 tissue) and oysters (Ostrea edulis: 0.42–1.04 μg DA g−1 tissue). The amount of DA in the two species was below the EU guideline limits for shellfish (20 μg DA g−1).Within the phytoplankton community, potentially toxic diatoms were observed in high densities (104–106 cells l−1). Among the 9 established cultured strains, seven were identified as the recently described species Nitzschia bizertensis sp. nov, which is apparently a commonly occurring species in the Bizerte Lagoon. Among tested five strains of N. bizertensis, four were confirmed to be toxin producers, containing 2–7 × 10−3 pg DA cell−1 during stationary growth phase.Our results indicate for the first time a Nitzschia species, here Nitzschia bizertensis, could be in relation to accumulation of DA in shellfish. Monitoring of DA in phytoplankton and shellfish should be considered for Bizerte Lagoon in order to gain knowledge about the ecology and toxin-production of N. bizertensis and to explore the risk of DA accumulation in the local shellfish industry caused by this species.

Habitat-specific differences in adaptation to light in freshwater diatoms

The growth and physiological characteristics of eight strains of diatoms isolated from aquatic habitats with differing water column characteristics were studied under varying light intensities to compare adaptations to low and high light intensity. Diatoms isolated from different habitats were grouped into low light-adapted (LLA) and high light-adapted (HLA) diatoms based on their differences in growth and photoacclimation characteristics. LLA diatoms had higher growth rates and higher photosynthetic activity at relatively lower light intensities (2, 12.5, and 25 μmol photons m−2 s−1) compared to relatively higher light intensities (60 and 80 μmol photons m−2 s−1). HLA diatoms had higher growth rates and higher photosynthetic activity at relatively higher light intensities (60 and 80 μmol photons m−2 s−1) compared to relatively lower light intensities (2, 12.5 and 25 μmol photons m−2 s−1). LLA diatoms responded to high light by enhancing non-photochemical quenching (NPQ) while HLA diatoms responded to low light mainly by increasing chlorophyll a content. Habitat-specific differences in adaptation to light in diatoms led to differences in light intensity for the formation of diatom blooms in low-light ecosystems and high-light ecosystems. Based on the results of this study, we suggest that the adaptability of diatoms to local habitat conditions should be considered in order to understand the photosynthetic characteristics of these diatom species.

Quantifying environmental stress-induced emissions of algal isoprene and monoterpenes using laboratory measurements

Abstract. We report here production rates of isoprene and monoterpene compounds (α-pinene, β-pinene, camphene and d-limonene) from six phytoplankton monocultures as a function of irradiance and temperature. Irradiance experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana), prymnesiophyte strains (Pleurochrysis carterae), dinoflagellate strains (Karenia brevis and Prorocentrum minimum), and cryptophyte strains (Rhodomonas salina), while temperature experiments were carried out for diatom strains (Thalassiosira weissflogii and Thalassiosira pseudonana). Phytoplankton species, incubated in a climate-controlled room, were subject to variable light (90 to 900 μmol m−2 s−1) and temperature (18 to 30 °C) regimes. Compared to isoprene, monoterpene emissions were an order of magnitude lower at all light and temperature levels. Emission rates are normalized by cell count and Chlorophyll a (Chl a) content. Diatom strains were the largest emitters, with ~ 2 × 10−17 g(cell)−1h−1 (~ 35 μg (g Chl a)−1 h−1) for isoprene and ~ 5 × 10−19 g (cell)−1 h−1 (~ 1 μg (g Chl a)−1) h−1) for α-pinene. The contribution to the total monoterpene production was ~ 70% from α-pinene, ~ 20% for d-limonene, and < 10% for camphene and β-pinene. Phytoplankton species showed a rapid increase in production rates at low irradiance (< 150 μmol m−2 s−1) and a gradual increase at high (> 250 μmol m−2 s−1) irradiance. Measurements revealed different patterns for time-averaged emissions rates over two successive days. On the first day, most of the species showed a distinct increase in production rates within the first 4 h while, on the second day, the emission rates were overall higher, but less variable. The data suggest that enhanced amounts of isoprene and monoterpenes are emitted from phytoplankton as a result of perturbations in environmental conditions that cause imbalance in chloroplasts and force primary producers to acclimate physiologically. This relationship could be a valuable tool for development of dynamic ecosystem modeling approaches for global marine isoprene and monoterpene emissions based on phytoplankton physiological responses to a changing environment.

五株北极微藻的藻际细菌多样性分析

As an important primary producer in the marine ecosystem,phytoplankton cells excrete organic compounds.These include high proportions of carbohydrates,amino acids and organic acids,including glycolic acid which forms the base of the marine microbial food web,and affects bacterial growth. Bacteria can live free in the phycosphere and also attached to the surface of algal cells,consuming extracellular products and consequently participate in biogeochemical cycling. Phytoplankton-bacteria interactions range from symbiotic to parasitic interactions,which play an important part in the microbial loop. However,research into phytoplankton-bacterium interactions is limited and yet to be published. The object of this study was to determine the specific associations between dominant algae and associated bacteria in the North Polar Region. We analyzed bacterial diversity in the phycosphere of four Arctic marine microalgae isolates( Micromonas sp.,Fragilariopsis sp.,Attheya septentrionalis and Thalassiosira sp.) and one glacial isolate,Chlorella sp.. Fragilariopsis sp.,Attheya septentrionalis,and Thalassiosira sp. belong to Bacillariophyta,while Chlorella sp. and Micromonas sp. belong toChlorophyta. The 16 S rRNA gene of the attached and free bacteria related to these five microalgae during different growth phases was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis. The associated bacterial diversity based on DGGE profiles was rich. These bacteria were clustered into Cyanobacteria, CFB, α-Proteobacteria, β-Proteobacteria,and γ-Proteobacteria. Bacteria in the phycosphere of marine isolates Micromonas sp.,Fragilariopsis sp.,Attheya septentrionalis and Thalassiosira sp. mainly belonged to cyanobacteria,α-Proteobacteria and γ-Proteobacteria. CFB was detected only in the phycosphere of Micromonas sp. and Fragilariopsis sp. With regard to the only glacial isolate Chlorella sp.,cyanobacteria,CFB,α-Proteobacteria,and β-Proteobacteria were detected in the majority. Differences in the dominant bacterial species of each microalgae,were distinguished. Cyanobacteria and α-Proteobacteria were detected in the phycosphere of these microalgae. Cyanobacteria bands from Fragilariopsis sp.,Attheya septentrionalis and Chlorella sp.differed from those of Micromonas sp. and Thalassiosira sp. Sulfitobacter of α-Proteobacteria coexisted with both Fragilariopsis sp. and Thalassiosira sp. β-Proteobacteria was traced only from the glacial isolate Cholrella sp. γ-Proteobacteria was commonly detected in the four marine microalgal cultures except the glacial isolate Chlorella sp..Shewanella was found closely associated with Micromonas sp., Attheya septentrionalis and Fragilariopsis sp., while Pseudoalteromonas was associated with Attheya septentrionalis and Fragilariopsis sp. and Thalassiosira sp. DGGE profiles and clustering analysis showed that the attached and free bacteria associated with Fragilariopsis sp. during the lag phase,exponential phase and stationary phase varied,except that the dominant bacteria was constant. Free bacteria in the phycosphere of the three diatom strains were claded into γ-Proteobacteria,while free bacteria associated with Chlorella sp.was clustered into β-Proteobacteria. Meanwhile,attached bacteria associated with these four microalgae were comprised mainly of cyanobacteria. However,the attached and free bacteria from the other four microalgae strains were invariable,indicating stability of the bacterial community structure in the phycosphere,except for a slight variation in the abundance of the dominant bacteria. The associated bacterial community related to the Arctic microalgae isolations was analyzed and it would help us recognize the mechanism of phytoplankton-bacteria interaction and their coexisting contribution in the Arctic ecosystem.

Taxonomic reference libraries for environmental barcoding: a best practice example from diatom research.

DNA barcoding uses a short fragment of a DNA sequence to identify a taxon. After obtaining the target sequence it is compared to reference sequences stored in a database to assign an organism name to it. The quality of data in the reference database is the key to the success of the analysis. In the here presented study, multiple types of data have been combined and critically examined in order to create best practice guidelines for taxonomic reference libraries for environmental barcoding. 70 unialgal diatom strains from Berlin waters have been established and cultured to obtain morphological and molecular data. The strains were sequenced for 18S V4 rDNA (the pre-Barcode for protists) as well as rbcL data, and identified by microscopy. LM and for some strains also SEM pictures were taken and physical vouchers deposited at the BGBM. 37 freshwater taxa from 15 naviculoid diatom genera were identified. Four taxa from the genera Amphora, Mayamaea, Planothidium and Stauroneis are described here as new. Names, molecular, morphological and habitat data as well as additional images of living cells are also available electronically in the AlgaTerra Information System. All reference sequences (or reference barcodes) presented here are linked to voucher specimens in order to provide a complete chain of evidence back to the formal taxonomic literature.

Kinetic exploration of nitrate-accumulating microalgae for nutrient recovery.

Within sustainable resource management, the recovery of nitrogen and phosphorus nutrients from waste streams is becoming increasingly important. Although the use of microalgae has been described extensively in environmental biotechnology, the potential of nitrate-accumulating microalgae for nutrient recovery has not been investigated yet. The ability of these marine microorganisms to concentrate environmental nitrate within their biomass is remarkable. The aim of this study was to investigate the application potential of nitrate-accumulating diatoms for nutrient recovery from marine wastewaters. The intracellular nitrate storage capacity was quantified for six marine diatom strains in synthetic wastewater. Amphora coffeaeformis and Phaeodactylum tricornutum stored the highest amount of nitrate with respectively 3.15 and 2.10 g N L(-1) of cell volume, which accounted for 17.3 and 4.6 %, respectively, of the total nitrogen content. The growth and nitrate and phosphate uptake of both diatoms were further analyzed and based on these features P. tricornutum showed the highest potential for nutrient recovery. A mathematical model was developed which included intracellular nitrate storage and the kinetic parameters were derived for P. tricornutum. Furthermore, a simulation study was performed to compare the performance of a proposed microalgal nutrient recovery unit with a conventional denitrification system for marine wastewater treatment. Overall, this study demonstrates the potential application of P. tricornutum for saline wastewater treatment with concurrent nitrogen and phosphorus recycling.

Purification and culture characteristics of 36 benthic marine diatoms isolated from the Solthörn tidal flat (Southern North Sea).

Marine benthic diatoms growing in biofilms on sediment surfaces generally occur associated with heterotrophic bacteria, whereas modern molecular techniques and analyses of species-specific physiology create a demand for axenic cultures. Numerous benthic diatoms were isolated from surface sediments during a monitoring of the Solthörn tidal flat (southern North Sea, Germany) from May 2008 to May 2009. Of these, around 50% could be purified from the accompanying heterotrophic bacteria using different antibiotics combined with physical separation methods (vortexing, ultrasound). Overall, seven different antibiotics were tested at different concentrations, and a best working protocol was developed. The axenic strains were stable on average for only around 15months, indicating a symbiotic interaction between the benthic diatoms and the associated bacteria. While most short-term effects during the purification process were restricted to differences in growth rates among xenic and axenic diatom strains, long-term cultivation led to distinct changes in cell volumes and growth characteristics of the axenic strains.

Combining multiple nutrient stresses and bicarbonate addition to promote lipid accumulation in the diatom RGd-1

Algal biofuels represent a renewable, potentially viable, solution to mitigate transportation fuel demands. A novel diatom strain, RGd-1, isolated from Yellowstone National Park, produces high concentrations of lipids that can be converted to biodiesel. To increase the cell concentration and determine optimal conditions for growth, RGd-1 was grown without added Si, in the presence of four Si concentrations within the soluble range (0.5–2mM), and one above the soluble range (2.5mM). Medium Si concentrations and intracellular triacylglycerol (TAG) content were monitored daily by inductively coupled plasma mass spectrometry and Nile Red fluorescence, respectively (end-point TAG values were measured using gas chromatography). Si depletion with or without combined nitrate (NO3−) limitation was shown to induce TAG accumulation. Additionally, the effects of sodium bicarbonate (NaHCO3) supplementation were examined on cultures grown using two NO3− concentrations (2.94 and 1mM NO3−), which also resulted in increased TAG accumulation. It was determined that utilizing a combination of two independent physiological stresses and HCO3− supplementation resulted in the highest total and per cell TAG accumulation.

The diatom Thalassiosira faurii (Gasse) Hasle in the Ziway–Shala lakes (Ethiopia) and implications for paleoclimatic reconstructions: Case study of the Glacial–Holocene transition in East Africa

The species Thalassiosira faurii (Gasse) Hasle was found dominating the planktonic diatom community during summer 2012 in Lake Langano which is part of the Ziway–Shala alkaline lake system in Ethiopia. In a previous study, the species had been recorded in high abundance in 13.5–12calka old sediments from the neighbor Lake Abiyata. Using a transfer function for conductivity, peaks in abundance had been interpreted as dry spells at the Pleistocene–Holocene transition since the species was considered strictly halophilous.In this study, a strain of Thalassiosira faurii was isolated from Lake Langano and grown in the laboratory. The observation of its morphology and reproduction, and comparison between modern and fossil populations helped to improve the taxonomic definition of the species. The autecology of the species was also investigated through a salinity tolerance test. The results revealed that the species was much more sensitive to salinity than previously believed. A new conductivity optimum was derived from the experiment and incorporated into the transfer function. The reassessment of lake conductivity variations along the core of Lake Abiyata showed that the intensity of the dry periods preceding the onset of the Holocene had been probably over-estimated.The reconsideration of the species relationship to conductivity may have important consequences for paleoclimatic reconstructions in tropical Africa where Thalassiosira faurii has been reported in abundance. The use of experimentation on local diatom strains allows paleoecologists to solve the problems of low representation of some species in modern dataset and of regional autecological variability within morphotypes.

Characterization of the triacylglycerol profile in marine diatoms by ultra performance liquid chromatography coupled with electrospray ionization–quadrupole time-of-flight mass spectrometry

Diatoms are considered to have great potential as new biofuel sources because they can effectively accumulate triacylglycerols (TAGs). Detailed structure information of TAG in diatoms is much needed not only for the assessment of biofuel quality such as fatty acid chain length and unsaturation degree but also for the tracing of biosynthetic precursors because the biosynthesis of TAG is typically completed by utilizing the diacylglycerol acyltransferase in the cytoplasm. In this report, a comprehensive characterization of TAGs in marine diatoms was performed using ultra performance liquid chromatography–electrospray ionization–quadrupole time-of-flight mass spectrometry. Many types of major TAGs were identified for the first time in these diatoms: 12 TAGs in Chaetoceros debilis, 9 TAGs in Phaeodactylum tricornutum Bohlin, 16 TAGs in Nitzschia closterium f. minutissima, 16 TAGs in Thalassiosira weissflogii, 13 TAGs in Thalassiosira sp., 16 TAGs in Stephanodiscus asteaea and 7 TAGs in Skeletonema costatum. Semi-quantification of TAGs in these diatoms was also carried out, and it was found that the contents of individual TAGs ranged from 0.5 ± 0.1 to 217.9 ± 8.1 nmol mg−1 total lipids. In addition, the total lipid contents in diatoms ranged from 143.6 ± 16.3 to 201.1 ± 16.3 mg g−1 dry microalgae and the total TAG contents ranged from 36.8 ± 9.5 to 793.2 ± 54.4 nmol mg−1 total lipids. By comparative analysis of the compositions and concentrations of major TAGs in the seven algal strains, N. closterium f. minutissima with high abundance of TAGs containing the most monounsaturated fatty acids (mainly palmitoleic acid) was considered as one of the most promising diatom strains for microalgal biofuel production. Additionally, based on the information of sn-2 fatty acid obtained (mainly C16 in the sn-2 position), we propose the hypothesis that TAGs in diatoms are mainly derived from lipids in chloroplasts through the prokaryotic biosynthesis pathway, including monogalactosyldiacylglycerol and digalactosyldiacylglycerol.

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) applied to diatom identification: influence of culturing age

Diatom identification is based on classical morphological methods focused on frus- tule shape and ornamentation analysis and possible chain formation. Because many morphologi- cal aspects are common to several species, diatom identification and characterisation are time- consuming and demand significant expertise. Furthermore, the use of advanced microscopy, such as transmission electron microscopy or scanning electron microscopy, is frequently necessary to differentiate these organisms. Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) was used to differentiate diatom taxa, and this report presents a preliminary study of the possibility of using this technique to obtain reliable fingerprinting of diatoms in the range of 2 to 20 kDa. Seminavis robusta, Coscinodiscus sp., Thalassiosira sp. and Cyclotella meneghiniana were used. The influence of culture age on reproducibility was studied. MALDI-TOF MS spectra were shown to vary with culturing time, and the need to consider this when setting up experimental standard conditions in the identification of diatoms was clearly established. One of the most important observations was that each diatom strain presented a specific age when the mass spectrum became reproducible. For all S. robusta strains and for C. meneghiniana, this age was 9 d, and for Thalassiosira sp. and Coscinodiscus sp., this age was 13 d. Even with the limitations of culture aging versus spectra reproducibility, MALDI-TOF MS proved to be a useful complementary tool to identify and characterise diatoms at the genus level. However, it was not possible to distinguish different mating types within the same species, as evidenced by the results obtained with S. robusta isolates.

Effects of Grazer Presence on Genetic Structure of a Phenotypically Diverse Diatom Population

Studies of predator-prey systems in both aquatic and terrestrial environments have shown that grazers structure the intraspecific diversity of prey species, given that the prey populations are phenotypically variable. Populations of phytoplankton have traditionally considered comprising only low intraspecific variation, hence selective grazing as a potentially structuring factor of both genetic and phenotypic diversity has not been comprehensively studied. In this study, we compared strain specific growth rates, production of polyunsaturated aldehydes, and chain length of the marine diatom Skeletonema marinoi in both grazer and non-grazer conditions by conducting monoclonal experiments. Additionally, a mesocosm experiment was performed with multiclonal experimental S. marinoi populations exposed to grazers at different levels of copepod concentration to test effects of grazer presence on diatom diversity in close to natural conditions. Our results show that distinct genotypes of a geographically restricted population exhibit variable phenotypic traits relevant to grazing interactions such as chain length and growth rates. Grazer presence affected clonal richness and evenness of multiclonal Skeletonema populations in the mesocosms, likely in conjunction with intrinsic interactions among the diatom strains. Only the production of polyunsaturated aldehydes was not affected by grazer presence. Our findings suggest that grazing can be an important factor structuring diatom population diversity in the sea and emphasize the importance of considering clonal differences when characterizing species and their role in nature.

Pigment Organization Effects on Energy Transfer and Chl a Emission Imaged in the Diatoms C. meneghiniana and P. tricornutum In Vivo: A Confocal Laser Scanning Fluorescence (CLSF) Microscopy and Spectroscopy Study

The (auto)fluorescence from three diatom strains, Cyclotella meneghiniana (Cm), Phaeodactylum tricornutum 1a (Pt1a), and Phaeodactylum UTex (PtUTex), has been imaged in vivo to submicrometer resolution using confocal laser scanning fluorescence (CLSF) microscopy. The diatoms are excited at 473 and 532 nm, energy primarily absorbed by the carotenoid fucoxanthin (Fx) found within the fucoxanthin chlorophyll a/c proteins (FCPs). On the basis of the fluorescence spectra measured in each image voxel, we obtain information about the spatial and energetic distribution of the terminal Chl a emitters, localized in the FCPs and the reaction centers of the PSII protein complexes, and the nature and location of the primary absorbers that are linked to these emitters; 532 nm excites the highly efficient Fx(red) light harvesters, and lesser amounts of Fx(green)s, that are enriched in some FCPs and preferentially transfer energy to PSII, compared to 473 nm, which excites almost equal amounts of all three previously identified sets of Fx--Fx(red), Fx(green) and Fx(blue)--as well as Chl c. The heterogeneous Chl a emission observed from the (C)LSF images indicates that the different Fx's serve different final emitters in P. tricornutum and suggest, at least in C. meneghiniana , a localization of FCPs with relatively greater Fx(red) content at the chloroplast edges, but with overall higher FCP concentration in the interior of the plastid. To better understand our results, the concentration-dependent ensemble-averaged diatom solution spectra are compared to the (auto)fluorescence spectra of individual diatoms, which indicate that pigment packing effects at an intracellular level do affect the diatoms' spectral properties, in particular, concerning a 710 nm emission band apparent under stress conditions. A species-specific response of the spectral signature to the incident light is also discussed in terms of the presence of a silica shell in Cm but not in Pt1a nor PtUTex.

TRIGLYCERIDE COMPOSITION OF SIXTEEN STRAINS OF MARINE DIATOM

Trigliceride or triacylglicerol (TAG) composition in crude oil of sixteen strain of marine diatom has been detected by spectra analyses on an Electrospray - Ion Trap – Mass Spectrometry (ESI-IT-MS) HCT Bruker-Daltonic GmbH instrument with AgNO3 used as coordination ionization agent. Biomass samples of each microalga strain were taken from early and late stationary cultures in f/2 enriched seawater and algal oils were extracted according to Bligh and Dyer. Results from spectra analysis showed that P-Pt-P (C16:0-C16:1-C16:0) were distinguished in TAG from diatom strains Chaetoceros sp.1, Chaetoceros sp.2, Thalasiossira sp.1, Thalasiossira sp.2, Thalasiossira sp.3, Navicula sp. 1, Navicula sp. 2, Navicula sp. 3, Navicula sp. 4, Nitzschia sp. 2 and Amphora sp. In contrast, TAGs in Melosira sp. included P-P-P (C16:0-C16:0-C16:0) and P-P-O (C16:0-C16:0-C18:1) were identified. TAGs from Chaetoceros sp. were the most varies among samples, i.e. P-Pt-P (C16:0-C16:1-C16:0), A-P-M (C20:4-C16:0-C14:0), P-Pt-Lt (C16:0-C16:1-C18:3), P-Pt-A (C16:0-C16:1-C20:4), D-P-P (C22:6-C16:0-C16:0), A-Ln-P (C20:4-C18:2-C16:0). Various TAGs were also detected in Nitzschia sp.2, i.e. P-Pt-M (C16:0-C16:1-C14:0), P-Pt-P (C16:0-C16:1-C16:0), P-Pt-S (C16:0-C16:1-C18:0), P-Pt-A (C16:0-C16:1-C20:4). TAGs composition in Skeletonema strains that similar to those in Nitzschia sp.1 has longer carbon, i.e. P-P-O (C16:0-C16:0-C18:1), P-O-O (C16:0-C18:1-C18:1) and O-O-O (C18:1-C18:1-C18:1). TAGs with longer carbon chain and more double bond including highly unsaturated fatty acid C20:4 were increased with culture age in diatoms Chaetoceros sp.1, Chaetoceros sp.2, Thalasiossira sp.2, Navicula sp.1 and Nitzschia sp. 2.Keywords: diatom, TAG, ESI-IT-MS, f/2, early and late stationary

TRIGLYCERIDE COMPOSITION OF SIXTEEN STRAINS OF MARINE DIATOM

<p>Trigliceride or triacylglicerol (TAG) composition in crude oil of sixteen strain of marine diatom has been detected by spectra analyses on an Electrospray - Ion Trap – Mass Spectrometry (ESI-IT-MS) HCT Bruker-Daltonic GmbH instrument with AgNO3 used as coordination ionization agent. Biomass samples of each microalga strain were taken from early and late stationary cultures in f/2 enriched seawater and algal oils were extracted according to Bligh and Dyer. Results from spectra analysis showed that P-Pt-P (C16:0-C16:1-C16:0) were distinguished in TAG from diatom strains Chaetoceros sp.1, Chaetoceros sp.2, Thalasiossira sp.1, Thalasiossira sp.2, Thalasiossira sp.3, Navicula sp. 1, Navicula sp. 2, Navicula sp. 3, Navicula sp. 4, Nitzschia sp. 2 and Amphora sp. In contrast, TAGs in Melosira sp. included P-P-P (C16:0-C16:0-C16:0) and P-P-O (C16:0-C16:0-C18:1) were identified. TAGs from Chaetoceros sp. were the most varies among samples, i.e. P-Pt-P (C16:0-C16:1-C16:0), A-P-M (C20:4-C16:0-C14:0), P-Pt-Lt (C16:0-C16:1-C18:3), P-Pt-A (C16:0-C16:1-C20:4), D-P-P (C22:6-C16:0-C16:0), A-Ln-P (C20:4-C18:2-C16:0). Various TAGs were also detected in Nitzschia sp.2, i.e. P-Pt-M (C16:0-C16:1-C14:0), P-Pt-P (C16:0-C16:1-C16:0), P-Pt-S (C16:0-C16:1-C18:0), P-Pt-A (C16:0-C16:1-C20:4). TAGs composition in Skeletonema strains that similar to those in Nitzschia sp.1 has longer carbon, i.e. P-P-O (C16:0-C16:0-C18:1), P-O-O (C16:0-C18:1-C18:1) and O-O-O (C18:1-C18:1-C18:1). TAGs with longer carbon chain and more double bond including highly unsaturated fatty acid C20:4 were increased with culture age in diatoms Chaetoceros sp.1, Chaetoceros sp.2, Thalasiossira sp.2, Navicula sp.1 and Nitzschia sp. 2.</p><p>Keywords: diatom, TAG, ESI-IT-MS, f/2, early and late stationary</p>

Next‐generation sequencing to inventory taxonomic diversity in eukaryotic communities: a test for freshwater diatoms

The recent emergence of barcoding approaches coupled to those of next-generation sequencing (NGS) has raised new perspectives for studying environmental communities. In this framework, we tested the possibility to derive accurate inventories of diatom communities from pyrosequencing outputs with an available DNA reference library. We used three molecular markers targeting the nuclear, chloroplast and mitochondrial genomes (SSU rDNA, rbcL and cox1) and three samples of a mock community composed of 30 known diatom strains belonging to 21 species. In the goal to detect methodological biases, one sample was constituted directly from pooled cultures, whereas the others consisted of pooled PCR products. The NGS reads obtained by pyrosequencing (Roche 454) were compared first to a DNA reference library including the sequences of all the species used to constitute the mock community, and second to a complete DNA reference library with a larger taxonomic coverage. A stringent taxonomic assignation gave inventories that were compared to the real one. We detected biases due to DNA extraction and PCR amplification that resulted in false-negative detection. Conversely, pyrosequencing errors appeared to generate false positives, especially in case of closely allied species. The taxonomic coverage of DNA reference libraries appears to be the most crucial factor, together with marker polymorphism which is essential to identify taxa at the species level. RbcL offers a high resolving power together with a large DNA reference library. Although needing further optimization, pyrosequencing is suitable for identifying diatom assemblages and may find applications in the field of freshwater biomonitoring.

Species-dependent silicon isotope fractionation by marine diatoms

Fractionation of silicon (Si) isotopes was measured in seven species (nine strains) of polar and sub-polar marine diatoms grown in semi-continuous unialgal cultures under optimal irradiance and temperature for each diatom strain. Results from this work provide the first evidence that Si isotope fractionation by diatoms is species-dependent. The greatest difference in the Si isotope fractionation factor (ε) was observed between two Southern Ocean diatoms, Fragilariopsis kerguelensis (−0.54‰, average for two strains) and Chaetoceros brevis (−2.09‰). The ε for the other species, both polar and sub-polar, ranged from −0.72‰ to −1.21‰. The two remaining polar diatoms had ε values of −0.74±0.05‰ for Thalassiosira antarctica, and −1.21±0.04‰ for Thalassiosira nordenskioeldii, while the sub-polar species had ε values of −0.72±0.04‰ for Thalassiosira weissflogii, −0.88±0.06‰ for Thalassiosira pseudonana (CCCM58), −0.97±0.14‰ for Thalassiosira pseudonana (CCMP1014), and −1.15±0.03‰ for Porosira glacialis. The range in ε for the diatoms evaluated in this study may be large enough to significantly impact the Si isotope composition measured in diatom opal (δ30Si-bSiO2) from marine sediments and its subsequent interpretation. To test the influence of diatom taxonomic composition on δ30Si-bSiO2, we developed a model that considered the relative abundance of diatom species and the ε values (from this study) for each species present within the sediment core (i.e. weighted-average ε). The model was applied to records from a Southern Ocean sediment core (TN057-13) where both diatom abundance and δ30Si-bSiO2 data were available. The analysis indicated that 67% of the variation in δ30Si-bSiO2 could be explained by species-dependent Si isotope fractionation. We suggest that future work should assess phytoplankton taxonomic composition when using δ30Si-bSiO2 as a proxy for Si utilization.

<p class="HeadingRunIn"><strong>Small diatoms (Bacillariophyta) in cultures from the Styx River, New Zealand, including descriptions of three new species</strong></p>

We obtained morphological and molecular data for 12 strains of small culturable diatoms from the Styx River, a semi-urban catchment in Christchurch, New Zealand, associated with high nutrient levels and increasing development pressure. Sellaphora styxii, Planothidium victori, and Eolimna krummensis are described as new to science, and material referable to the Nitzschia palea complex is genetically distinctive and would represent a new species if the genus was revised. E. krummensis had already been sequenced (but not described or named) from Europe. The other strains, Planothidium frequentissimum, Gomphonema parvulum, Fistulifera saprophila, Navicula cryptocephala, N. veneta, Craticula molestiformis, and Cyclotella meneghiniana are well known from the Northern Hemisphere; thus 3 of the 12 strains are presently known only from New Zealand. It is difficult to evaluate the likelihood of their endemism, but we expect that they will ultimately be found to be cosmopolitan. Infraspecific distribution patterns could be evaluated with molecular data, but would require the widespread sequencing of more variable gene regions.