An Oil Hyper-Accumulator Mutant Highlights Peroxisomal ATP Import as a Regulatory Step for Fatty Acid Metabolism in Aurantiochytrium limacinum.

Thraustochytrids are marine protists that naturally accumulate triacylglycerol with long chains of polyunsaturated fatty acids, such as ω3-docosahexaenoic acid (DHA). They represent a sustainable response to the increasing demand for these "essential" fatty acids (FAs). Following an attempt to transform a strain of Aurantiochytrium limacinum, we serendipitously isolated a clone that did not incorporate any recombinant DNA but contained two to three times more DHA than the original strain. Metabolic analyses indicated a deficit in FA catabolism. However, whole transcriptome analysis did not show down-regulation of genes involved in FA catabolism. Genome sequencing revealed extensive DNA deletion in one allele encoding a putative peroxisomal adenylate transporter. Phylogenetic analyses and yeast complementation experiments confirmed the gene as a peroxisomal adenylate nucleotide transporter (AlANT1), homologous to yeast ScANT1 and plant peroxisomal adenylate nucleotide carrier AtPNC genes. In yeast and plants, a deletion of the peroxisomal adenylate transporter inhibits FA breakdown and induces FA accumulation, a phenotype similar to that described here. In response to this metabolic event, several compensatory mechanisms were observed. In particular, genes involved in FA biosynthesis were upregulated, also contributing to the high FA accumulation. These results support AlANT1 as a promising target for enhancing DHA production in Thraustochytrids.

Eustigmatophyte strains with potential interest in cancer prevention and treatment: partial chemical characterization and evaluation of cytotoxic and antioxidant activity.

The interest in bioactive compounds from microalgae is increasing since they have medicinal and nutritional areas. The present work aims to evaluate the potential pharmaceutical interest of extracts from three eustigmatophyte strains from the Coimbra Collection of Algae (ACOI): Chlorobotrys gloeothece, Chlorobotrys regularis and Characiopsis aquilonaris. Antioxidant and antiproliferative activities were determined as well as chlorophyll a, carotenoid and phenolic total contents. In addition, major pigments and sterols were identified and quantified. The three strains were grown until the stationary phase and then the biomass was extracted. Antioxidant activity was measured by TEAC, DPPH and FRAP assays and antiproliferative effect was assessed by the MTT method on MCF-7, PC-3 and NHDF cells. The pigment and phenolic total contents were determined by spectrophotometry. Of these strains, C. aquilonaris showed the highest antioxidant activity measured by TEAC and FRAP assays (23.98 ± 0.01 µmol TE eq g-1 DW and 42.57 ± 0.04 µmol TE eq g-1 DW, respectively), a selective effect in reduting MCF-7 cells proliferation and a larger amount of chlorophyll a, carotenoids and phenolic content (18.40 ± 0.00 µg chlorophyll a mg-1 DW, 2.27 ± 0.00 mg carotenoids g-1 DW and 6.23 ± 0.01 mg GAE g-1 DW, respectively). A positive correlation between chlorophyll a and TEAC assay was observed, as well as between carotenoids and TEAC and FRAP assays, suggesting these compounds as important contributors to significant antioxidant activity. Violaxanthin, cholesterol and stigmasterol were present in larger amount in C. aquilonaris while C. regularis showed a higher amount of ß-carotene. These results suggest that these three ACOI eustigmatophytes are promising for applications in the improvement of human health, particularly in cancer prevention and treatment.

Antioxidant Bioprospecting in Microalgae: Characterisation of the Potential of Two Marine Heterokonts from Irish Waters.

Microalgae constitute a heterogeneous and diverse range of organisms capable of accumulating bioactive metabolites, making them promising feedstock for applications in the nutraceutical, functional food, animal feed, biofertilisation or biofuel sectors. There has been renewed interest in recent times in natural sources of antioxidants, particularly as health products and preserving agents. Microalgae strains isolated from aquatic habitats in Ireland were successfully brought into culture. The 91 strains were grown phototrophically in nutrient-enriched media to generate biomass, which was harvested and assessed for antioxidant potential. Extracts were screened for antioxidant activity using a modified volumetric Trolox-ABTS assay and the Folin-Ciocalteu method. Two heterokont marine strains of interest were further studied to ascertain variations in antioxidant capacity across different stages of batch culture growth. The antioxidant activity of extracts of bacillariophyte cf. Stauroneis sp. LACW24 and ocrophyte cf. Phaeothamnion sp. LACW34 increased during growth with a maximum being observed during the late stationary or early death phase (2.5- to 8-fold increases between days 20 and 27). Strains LACW24 and LACW34 contained 5.9 and 3.0 mg g-1 (DW) of the xanthophyll fucoxanthin, respectively. Extracts of strains also showed no cytotoxicity towards mouse cell lines. These results highlight the potential of these strains for biomass valorisation and cultivation upscaling and to be further considered as part of ongoing bioprospecting efforts towards identifying novel species to join the relatively narrow range of commercially exploited marine microalgae species.

Effect of water accommodated fractions of fuel oil on fixed carbon and nitrogen by microalgae: Implication by stable isotope analysis.

Effect of water accommodated fractions (WAF) of #180 fuel oil on fixed carbon and nitrogen in microalgae was studied by stable isotopes. Platymonas helgolandica, Heterosigma akashiwo and Nitzschia closterium were exposed to five WAF concentrations for 96 h. The δ13C value of microalgae was significantly lower than that of the control group, indicated that carbon was limited in the WAF concentrations. The δ13C value of microalgae appeared peak valley at 48 h in control group, corresponding to the enhanced capacity in carbon fixation during microalgae photosynthesis. The physiological acclimation capacity of microalgae was revealed by the occurrence time when the δ13C value was in peak valley, and thus the physiological acclimation capacity of microalgae decreased in the order of Nitzschia closterium > Heterosigma akashiwo > Platymonas helgolandica. Principal component analysis (PCA) were applied to the δ13C value in order to verify the "hormesis" phenomenon in microalgae. The δ13C value could discriminate between stimulatory effects at low doses and inhibitory effects at high doses. In addition, the present study also investigated the effect of the nitrogen on microalgae growth. Because microalgae could still absorb the NO3-N and release of NO2-N and NH4-N in present study, the nitrogen cycle in microalgae was in the equilibrium status. The δ15N value in microalgae exhibited no obvious change with the increasing of WAF concentrations at the same time. However, due to the enrichment of nitrogen, the δ15N value first increased gradually with the time and finally was stable. Overall, the fractionation of carbon and nitrogen stable isotopes illustrated that the effect of carbon on the growth of microalgae was more prominent than nitrogen. Stable isotopes was used to investigate the influence of WAF on fixed carbon and nitrogen in microalgae growth, providing a fundamental theoretical guidance for risk assessment of marine ecological environment.

Multifunctional fluorocarbon photobioreactor system: a novel integrated device for CO2 segregation, O2 collection, and enhancement of microalgae growth and bioproductions.

An enhanced greenhouse effect due to high CO2 emissions has become one of the most concerning issues worldwide. Although plant/algae-mediated approaches have been extensively used for CO2 segregation in the last decades, these methods are generally aimed at environment protection. In contrast, less attention has been given to CO2 manipulation that has regrettably caused a decrease in the commercial availability of the associated technologies. To generate a system for practical use, a synthetic fluorocarbon photobioreactor system (FCPBRS) consisting of a CO2 isolation unit, a gas modulation unit, an O2 collection unit, and a microalgal culture chamber was developed in this study. After injecting a 60%-N2/40%-CO2 gas mixture into the CO2 isolation unit for 10 days, the results showed that the FCPBRS enabled a > 93% CO2 separation efficiency using a fluorocarbon liquid FC-40 as the CO2 adsorbent. In addition, the growth rate of Nannochloropsis oculata was significantly enhanced when cultured with 20 mL min-1 of the FC-40 flow containing 2% CO2 throughout the time course, resulting in 4.7-, 4.6-, and 4.5-fold (P < 0.05 for each) increases in biomass, total lipid, and eicosapentaenoic acid yields, respectively, compared to the aerated group without FC-40. Moreover, approximately 1600 mL of photosynthetic O2 with a ~ 80% collection efficiency was obtained in the O2 collection unit within 10 days of FCPBRS operation. These outcomes indicate that the FCPBRS may provide a feasible means to simultaneously achieve CO2 isolation, O2 collection, and enhanced microalgae bioproductions.

Valorisation of the microalgae Nannochloropsis gaditana biomass by proteomic approach in the context of circular economy.

Nannochloropsis gaditana is a non-flagellated microalgae that has been widely used for different purposes, mostly related with the industrial production of biofuels or aquiculture. However, in order to increase the economic viability of the obtained microalgae biomass from a production plant coupled to a coal power plant, a proteomic approach was initiated by using fresh and atomized microalgae samples, as the main used commercial forms. Above 51,000 high quality spectra were obtained per sample in the MS/MS analysis of whole proteome of N. gaditana, yielding above 7,500 peptides, leading the identification of 1,950 proteins, from the N. gaditana protein database, where 655 proteins were presented in all the replicates. The identified proteins were categorized according to gene ontology classification by molecular function and biological process. In this study, it has been described the first proteomic analysis of the microalgae N. gaditana under industrial conditions containing an important number of identified proteins. A significative presence of proteins with a potential role in different agri-food and biomedical applications was detected and studied being the core of future N. gaditana research to expand the current biotechnological applications of this microalga. SIGNIFICANCE OF THE STUDY: Three quarters of the planet earth correspond to seas and oceans, however its potential biotechnological use is still unknown. We described the first proteomic description of the microalgae N. gaditana under industrial conditions. Following the spirit of the EU initiatives of blue growth and the statements of circular economy, CO2 waste from a coal plant power has been transformed in a resource for microalgae biomass production, common product presentations were evaluated by proteomic, and its potential use of identified proteins in Agri-food and Biomedicine has been revealed.

Enhanced production of carotenoids using a Thraustochytrid microalgal strain containing high levels of docosahexaenoic acid-rich oil.

Results to date suggest that microalgal Thraustochytrids family strains can be used to produce high-functional omega-3 rich oil (~ 30-70% of dry cell weight) and carotenoid-based antioxidant pigments simultaneously with value-added bioactive potential. In the present study, we describe the isolation and characterization of a new Thraustochytrid Schizochytrium sp. from the west coastal area of Korea. This newly isolated Thraustochytrid, identified as Schizochytrium sp. through 18S rRNA analysis and named SH104, simultaneously produces high levels of DHA and carotenoid-based antioxidant pigments. An improved Schizochytrium mutant, named SHG104, was obtained from the original host strain by γ-irradiation-induced mutagenesis. Under combined temperature-shift cultivation conditions employing white-light LEDs (light-emitting diodes), Schizochytrium sp. SHG104 yielded 10.8 g L-1 of biomass comprising 45.8% total lipids (32.1% DHA) and 4.6 mg L-1 of astaxanthin. In addition to DHA, the main fatty acids produced by Schizochytrium sp. SHG104 were palmitic acid and a trace of other long-chain fatty acids. The carotenoid profile of SH104 and SHG104 was ß-carotene, astaxanthin, canthaxanthin, pheonicoxanthin and echinenone, which analyzed by HPLC and LC/APCI-MS. Furthermore, genomic analysis of Schizochytrium and Aurantiochytrium microalgae confirmed that the presence of carotenogenesis pathway enzymes and genes including geranylgeranyl diphosphate, phytoene synthase, lycopene cyclase, and cytochrome P450 hydroxylase that necessary for the production of antioxidants via a complete biosynthetic KEGG synthesis pathway. This newly isolated Schizochytrium microalga potentially have wide application as a source of antioxidants for astaxanthin-containing pigments, commercial omega-3 lipids and feed additives, such as nutritional supplements for aquaculture.

Antigastric Cancer Bioactive Aurantiochytrium Oil Rich in Docosahexaenoic Acid: From Media Optimization to Cancer Cells Cytotoxicity Assessment.

Dietary eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) may have a role in contributing to the prevention or inhibition of some malignancies. DHA, the most important polyunsaturated fatty acid (PUFA) in fish and thraustochytrid oils, is known for its anticancer activity. However, antigastric cancer activity of thraustochytrid microbial oil is still unclear. In this investigation, 45 thraustochytrid strains were screened for the production of antigastric cancer oil. Cytotoxicity of 12 thraustochytrid oils was assessed by 3-(4,5-dimethythiazol- 2-yl)-2,5-diphenyl tetrazolium bromide (MTT) on gastric cancer AGS cells. The most cytotoxic effect was related to the oil extracted from the qe-4 strain with 45% cell cytotoxicity. Therefore, the Taguchi methodology was used to optimize this bioactive microbial oil. The amounts of biomass, oil, and DHA were increased to 10.32 g/L, 3.86 g/L, and 1390 mg/L, respectively. Furthermore, the use of glycerol in low saline medium enhanced the yield of DHA. Then, the cytotoxicity of thraustochytrids oil rich in DHA or C16 (0.5 to 10 mg/mL), was assessed on AGS cells. Only the oil that was rich in DHA showed an inhibitory effect (IC50 ) on AGS cells (same as the standard DHA at 1.26 mg/mL). These new findings revealed that thraustochytrid derived oil rich in DHA, has an inhibitory effect on gastric cancer cells. Phylogenetic analysis showed that qe-4 is related to the genus Aurantiochytrium (AN: KR091914) as a potential candidate for the production of bioactive oil. In conclusion, these results certainly support further investigations on this bioactive microbial oil as an additive for the fortification of food and dairy products. PRACTICAL APPLICATION: Thraustochytrid microbial oil rich in DHA, showed antigastric cancer activity comparable to that of pure DHA; indicating that this microbial bioactive omega-3 oil rich in the very important PUFA (DHA), can be applied as an additive for the fortification of food and dairy products. Also, Aurantiochytrium sp. KR091914, as a GRAS microorganism, is a good producer of this bioactive oil.

Production of docosahexaenoic acid by Aurantiochytrium sp. ATCC PRA-276

Abstract The high costs and environmental concerns associated with using marine resources as sources of oils rich in polyunsaturated fatty acids have prompted searches for alternative sources of such oils. Some microorganisms, among them members of the genus Aurantiochytrium, can synthesize large amounts of these biocompounds. However, various parameters that affect the polyunsaturated fatty acids production of these organisms, such as the carbon and nitrogen sources supplied during their cultivation, require further elucidation. The objective of this investigation was to study the effect of different concentrations of carbon and total nitrogen on the production of polyunsaturated fatty acids, particularly docosahexaenoic acid, by Aurantiochytrium sp. ATCC PRA-276. We performed batch system experiments using an initial glucose concentration of 30 g/L and three different concentrations of total nitrogen, including 3.0, 0.44, and 0.22 g/L, and fed-batch system experiments in which 0.14 g/L of glucose and 0.0014 g/L of total nitrogen were supplied hourly. To assess the effects of these different treatments, we determined the biomass, glucose, total nitrogen and polyunsaturated fatty acids concentration. The maximum cell concentration (23.9 g/L) was obtained after 96 h of cultivation in the batch system using initial concentrations of 0.22 g/L total nitrogen and 30 g/L glucose. Under these conditions, we observed the highest level of polyunsaturated fatty acids production (3.6 g/L), with docosahexaenoic acid and docosapentaenoic acid ω6 concentrations reaching 2.54 and 0.80 g/L, respectively.

Discovery of a resting stage in the harmful, brown-tide-causing pelagophyte, Aureoumbra lagunensis: a mechanism potentially facilitating recurrent blooms and geographic expansion.

To date, the life stages of pelagophytes have been poorly described. This study describes the ability of Aureoumbra lagunensis to enter a resting stage in response to environmental stressors including high temperature, nutrient depletion, and darkness as well as their ability to revert from resting cells back to vegetative cells after exposure to optimal light, temperature, and nutrient conditions. Resting cells became round in shape and larger in size, filled with red accumulation bodies, had smaller and fewer plastids, more vacuolar space, contained lower concentrations of chl a and RNA, displayed reduced photosynthetic efficiency, and lower respiration rates relative to vegetative cells. Analysis of vegetative and resting cells using Raman microspectrometry indicated resting cells were enriched in sterols within red accumulation bodies and were depleted in pigments relative to vegetative cells. Upon reverting to vegetative cells, cells increased their chl a content, photosynthetic efficiency, respiration rate, and growth rate and lost accumulation bodies as they became smaller. The time required for resting cells to resume vegetative growth was proportional to both the duration and temperature of dark storage, possibly due to higher metabolic demands on stored energy (sterols) reserves during longer period of storage and/or storage at higher temperature (20°C vs. 10°C). Resting cells kept in the dark at 10°C for 7 months readily reverted back to vegetative cells when transferred to optimal conditions. Thus, the ability of Aureoumbra to form a resting stage likely enables them to form annual blooms within subtropic ecosystems, resist temperature extremes, and may facilitate geographic expansion via anthropogenic transport.

Host genome integration and giant virus-induced reactivation of the virophage mavirus.

Endogenous viral elements are increasingly found in eukaryotic genomes, yet little is known about their origins, dynamics, or function. Here we provide a compelling example of a DNA virus that readily integrates into a eukaryotic genome where it acts as an inducible antiviral defence system. We found that the virophage mavirus, a parasite of the giant Cafeteria roenbergensis virus (CroV), integrates at multiple sites within the nuclear genome of the marine protozoan Cafeteria roenbergensis. The endogenous mavirus is structurally and genetically similar to eukaryotic DNA transposons and endogenous viruses of the Maverick/Polinton family. Provirophage genes are not constitutively expressed, but are specifically activated by superinfection with CroV, which induces the production of infectious mavirus particles. Virophages can inhibit the replication of mimivirus-like giant viruses and an anti-viral protective effect of provirophages on their hosts has been hypothesized. We find that provirophage-carrying cells are not directly protected from CroV; however, lysis of these cells releases infectious mavirus particles that are then able to suppress CroV replication and enhance host survival during subsequent rounds of infection. The microbial host-parasite interaction described here involves an altruistic aspect and suggests that giant-virus-induced activation of provirophages might be ecologically relevant in natural protist populations.

An Improved Quantitative Real-Time PCR Assay for the Enumeration of Heterosigma akashiwo (Raphidophyceae) Cysts Using a DNA Debris Removal Method and a Cyst-Based Standard Curve.

The identification and quantification of Heterosigma akashiwo cysts in sediments by light microscopy can be difficult due to the small size and morphology of the cysts, which are often indistinguishable from those of other types of algae. Quantitative real-time PCR (qPCR) based assays represent a potentially efficient method for quantifying the abundance of H. akashiwo cysts, although standard curves must be based on cyst DNA rather than on vegetative cell DNA due to differences in gene copy number and DNA extraction yield between these two cell types. Furthermore, qPCR on sediment samples can be complicated by the presence of extracellular DNA debris. To solve these problems, we constructed a cyst-based standard curve and developed a simple method for removing DNA debris from sediment samples. This cyst-based standard curve was compared with a standard curve based on vegetative cells, as vegetative cells may have twice the gene copy number of cysts. To remove DNA debris from the sediment, we developed a simple method involving dilution with distilled water and heating at 75°C. A total of 18 sediment samples were used to evaluate this method. Cyst abundance determined using the qPCR assay without DNA debris removal yielded results up to 51-fold greater than with direct counting. By contrast, a highly significant correlation was observed between cyst abundance determined by direct counting and the qPCR assay in conjunction with DNA debris removal (r2 = 0.72, slope = 1.07, p < 0.001). Therefore, this improved qPCR method should be a powerful tool for the accurate quantification of H. akashiwo cysts in sediment samples.

Gas Transfer Controls Carbon Limitation During Biomass Production by Marine Microalgae.

This study presents the first in-depth analysis of CO2 limitation on the biomass productivity of the biofuel candidate marine microalga Nannochloropsis oculata. Net photosynthesis decreased by 60% from 125 to 50 µmol O2 L(-1)h(-1) over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the photo-bioreactor. Gas exchange determined the degree of carbon limitation experienced by the algae. Carbon limitation was confirmed by delivering more CO2 , which increased net photosynthesis back to its steady-state maximum. This study highlights the importance of maintaining replete carbon concentrations in photo-bioreactors and other culturing facilities, either by constant pH operation or preferably by designing a feedback loop based on the dissolved O2 concentration.

Cultivation of marine microalgae using shale gas flowback water and anaerobic digestion effluent as the cultivation medium.

The potential of shale gas flowback water and anaerobic digestion (AD) effluent to reduce the water and nutrient requirements for marine microalgae cultivation was evaluated with the following strains: Nannochloropsis salina, Dunaliella tertiolecta, and Dunaliella salina. N. salina and D. tertiolecta achieved the highest biomass productivity in the medium composed of flowback water and AD effluent (6% v/v). Growth in the above unsterilized medium was found to be comparable to that in sterilized commercial media with similar initial inorganic nitrogen concentrations, salinity, and pH levels. Specific growth rates of 0.293 and 0.349 day(-1) and average biomass productivities of 225 and 275 mg L(-1)day(-1) were obtained for N. salina and D. tertiolecta, respectively. The lipid content and fatty acid profile of both strains in the medium were also comparable to those obtained with commercial nutrients and salts.

Large-scale biodiesel production using flue gas from coal-fired power plants with Nannochloropsis microalgal biomass in open raceway ponds.

The potential use of microalgal biomass as a biofuel source has raised broad interest. Highly effective and economically feasible biomass generating techniques are essential to realize such potential. Flue gas from coal-fired power plants may serve as an inexpensive carbon source for microalgal culture, and it may also facilitate improvement of the environment once the gas is fixed in biomass. In this study, three strains of the genus Nannochloropsis (4-38, KA2 and 75B1) survived this type of culture and bloomed using flue gas from coal-fired power plants in 8000-L open raceway ponds. Lower temperatures and solar irradiation reduced the biomass yield and lipid productivities of these strains. Strain 4-38 performed better than the other two as it contained higher amounts of triacylglycerols and fatty acids, which are used for biodiesel production. Further optimization of the application of flue gas to microalgal culture should be undertaken.

Unravelling the matrix effect of fresh sampled cells for in vivo unbiased FTIR determination of the absolute concentration of total lipid content of microalgae.

Over the past years, the substitution of the classical biochemical quantification techniques by Fourier transform infrared (FTIR) spectroscopy has been widely studied on microalgae because of its tremendous application potential for bioprocess monitoring. In the present work, mandatory aspects that have never been approached by FTIR end-users working onto fresh biomass were assessed. We demonstrated first that fresh cells' FTIR spectra main characteristics could be severely and unspecifically altered when the properties of the sampled biomass were not monitored. Microscopy indicated that important cell reorganization could occur when diminishing the cells density of the sample. Molecular probing approach suggested that such a modification could provoke an alteration of the hydrogen-bonding network of the sample. The sample heterogeneity was found to impact also the shape and intensity of the recorded FTIR bands, participating then to a matrix effect uncharacterized until now. In the second part of our study, we selected FTIR spectra not influenced by this matrix effect and the corresponding accurate calibration data obtained by the whole cell analytical procedure to elaborate an optimized total lipid quantification PLS-R model. Results demonstrated that our strategy could provide a small volume sampling (1 mL of fresh culture), rapid (within minutes), robust (physiological condition independent), and accurate (as accurate as the reference method could be) FTIR absolute quantification method to determine the fresh microalgae intracellular total lipid content. To validate our unbiased FTIR approach, a photobioprocess monitoring pipeline was developed and allowed assessing the effect of light attenuation on total lipid production by the marine microalga Nannochloropsis oculata.

Undocumented water column sink for cadmium in open ocean oxygen-deficient zones.

Cadmium (Cd) is a micronutrient and a tracer of biological productivity and circulation in the ocean. The correlation between dissolved Cd and the major algal nutrients in seawater has led to the use of Cd preserved in microfossils to constrain past ocean nutrient distributions. However, linking Cd to marine biological processes requires constraints on marine sources and sinks of Cd. Here, we show a decoupling between Cd and major nutrients within oxygen-deficient zones (ODZs) in both the Northeast Pacific and North Atlantic Oceans, which we attribute to Cd sulfide (CdS) precipitation in euxinic microenvironments around sinking biological particles. We find that dissolved Cd correlates well with dissolved phosphate in oxygenated waters, but is depleted compared with phosphate in ODZs. Additionally, suspended particles from the North Atlantic show high Cd content and light Cd stable isotope ratios within the ODZ, indicative of CdS precipitation. Globally, we calculate that CdS precipitation in ODZs is an important, and to our knowledge a previously undocumented marine sink of Cd. Our results suggest that water column oxygen depletion has a substantial impact on Cd biogeochemical cycling, impacting the global relationship between Cd and major nutrients and suggesting that Cd may be a previously unidentified tracer for water column oxygen deficiency on geological timescales. Similar depletions of copper and zinc in the Northeast Pacific indicate that sulfide precipitation in ODZs may also have an influence on the global distribution of other trace metals.

Biomass composition, lipid characterization, and metabolic profile analysis of the fed-batch fermentation process of two different docosahexanoic acid producing Schizochytrium sp. strains.

Growth and fermentation characteristics, biomass composition, lipid characterization and metabolic profiling analysis of two different Schizochytrium sp. strains, the original strain and the industrial adaptive strain, were investigated in the fed-batch fermentation process. The final cell biomass, total lipids content, docosahexanoic acid (DHA) content and DHA productivity of the adaptive strain were much higher than those of the original strain. The metabolic distinctions which extensively existed between these two strains were revealed by the score plot of principal component analysis. In addition, potential biomarkers responsible for discriminating different strains were identified as myo-inositol, histidine, alanine, asparagine, cysteine, and oxalic acid. These findings provided new insights into the industrial strain screening and further improvement of DHA production by Schizochytrium sp.

Growth-phase dependent variation in photosynthetic activity and cellular protein expression profile in the harmful raphidophyte Chattonella antiqua.

This study investigated temporal variations in the potential maximum quantum yield of photosystem II (F(v)/F(m) ratio) and growth-phase dependent cellular protein expressions of Chattonella antiqua under laboratory conditions. Despite the culture conditions, significant positive correlations between the F(v)/F(m) ratio and daily growth rate were observed. Threshold F(v)/F(m) ratios associated with positive cell growth were calculated to be >0.44, >0.44, and >0.37, and those associated with active cell growth (growth rate >0.5 div. d(-1)) were >0.58, >0.60, and >0.49 under control culture, low nutrient and intense light conditions, respectively. Proteome profiles obtained by two-dimensional gel electrophoresis (2-DE) indicated that 42 protein spots were differentially expressed at various growth phases of C. antiqua, which indicates changes in cellular physiological status throughout the growth cycle, and suggests that oxygen evolving enhancer 1 and 2-cysteine peroxiredoxin play roles in maintaining the positive growth of C. antiqua.

Toxicity of the xenoestrogen nonylphenol and its biodegradation by the alga Cyclotella caspia.

Alkylphenols (APs), the breakdown products of alkylphenol polyethoxylates that are widely used as surfactants, have been proven to exert estrogenic effects. With industrial development, higher concentrations of APs are discharged into aquatic environments. Nonylphenol (NP), the most noxious AP, is included in the blacklist of several countries. The toxicity of NP to the alga Cyclotella caspia and the biodegradation of NP by C. caspia were studied in the laboratory. The median effective concentration at 96 hr (96 hr EC50) of NP for C. caspia was found to be 0.18 mg/L. Five toxicity and three degradation indices were selected for toxicity and biodegradation experiments, respectively, in five or three concentrations of NP set by the 96 hr EC50 of NP. The algal growth rate and chlorophyll a contents decreased as NP concentration increased. The main manifestations of morphological deformity of the cells included volume expansion and the presence of cytoplasmic inclusions (lipid droplets). The abnormality rate of the cells increased with NP concentration and time, and was 100% at 0.22 and 0.26 mg/L of NP after 192 hr of culture. Superoxide dismutase activity initially increased and then declined at a higher NP toxicity of greater than 0.18 mg/L. After 192 hr of culture, the biodegradation rates of NP by C. caspia with initial concentrations of 0.14, 0.18, and 0.22 mg/L were 37.7%, 31.7%, and 6.5%, respectively. The kinetic equation of C. caspia biodegradation on NP was correlated with algal growth rate and initial NP concentration.