Coagulation and disinfection by-products formation potential of extracellular and intracellular matter of algae and cyanobacteria

Coagulation and flocculation can remove particulate algal cells effectively; however, they are not very effective for removing dissolved algal organic matter (AOM) in drinking water plants. In this work, optimum coagulation conditions using alum for both extracellular and intracellular organic matter of six different algal and cyanobacterial species were determined. Different coagulation conditions such as alum dosage, pH, and initial dissolved organic carbon (DOC) were tested. Hydrophobicity, hydrophilicty, and transphilicity of the cellular materials were determined using resin fractionation method. The removal of DOC by coagulation correlated well with the hydrophobicity of the AOM. The disinfection by-product formation potential (DBPFP) of various fractions of AOM was determined after coagulation. Although, higher removal occurred for hydrophobic AOM during coagulation, specific DBPFP, which varied from 10 to 147 μg/mg-C was higher for hydrophobic AOM. Of all the six species, highest DBPFP occurred for Phaeodactylum tricornutum, an abundant marine diatom species, but is increasingly found in surface water.

Laminarin is a major molecule in the marine carbon cycle

Marine microalgae sequester as much CO2 into carbohydrates as terrestrial plants. Polymeric carbohydrates (i.e., glycans) provide carbon for heterotrophic organisms and constitute a carbon sink in the global oceans. The quantitative contributions of different algal glycans to cycling and sequestration of carbon remain unknown, partly because of the analytical challenge to quantify glycans in complex biological matrices. Here, we quantified a glycan structural type using a recently developed biocatalytic strategy, which involves laminarinase enzymes that specifically cleave the algal glycan laminarin into readily analyzable fragments. We measured laminarin along transects in the Arctic, Atlantic, and Pacific oceans and during three time series in the North Sea. These data revealed a median of 26 ± 17% laminarin within the particulate organic carbon pool. The observed correlation between chlorophyll and laminarin suggests an annual production of algal laminarin of 12 ± 8 gigatons: that is, approximately three times the annual atmospheric carbon dioxide increase by fossil fuel burning. Moreover, our data revealed that laminarin accounted for up to 50% of organic carbon in sinking diatom-containing particles, thus substantially contributing to carbon export from surface waters. Spatially and temporally variable laminarin concentrations in the sunlit ocean are driven by light availability. Collectively, these observations highlight the prominent ecological role and biogeochemical function of laminarin in oceanic carbon export and energy flow to higher trophic levels.

Types and Distribution of Bioactive Polyunsaturated Aldehydes in a Gradient from Mesotrophic to Oligotrophic Waters in the Alborán Sea (Western Mediterranean)

Polyunsaturated aldehydes (PUAs) are bioactive molecules suggested as chemical defenses and infochemicals. In marine coastal habitats, diatoms reach high PUA production levels during bloom episodes. Two fractions of PUA can usually be analyzed: pPUA obtained via artificial breakage of collected phytoplankton cells and dissolved PUA already released to the environment (dPUA). In nature, resource supply arises as a main environmental controlling factor of PUA production. In this work, we monitored the vertical distribution and daily variation of pPUA associated with large-size phytoplankton and dPUA, at three sites located in the Alborán Sea from mesotrophic to oligotrophic waters. The results corroborate the presence of large-size PUA producers in oligotrophic and mesotrophic waters with a significant (58%-85%) diatom biomass. In addition to diatoms, significant correlations between pPUA production and dinoflagellate and silicoflagellate abundance were observed. 2E,4E/Z-Heptadienal was the most abundant aldehyde at the three sites with higher values (17.1 fg·cell-1) at the most oligotrophic site. 2E,4E/Z-Decadienal was the least abundant aldehyde, decreasing toward the oligotrophic site. For the first time, we describe the daily fluctuation of pPUA attributable to cellular physiological state and not exclusively to taxonomical composition. Our results demonstrate the persistence of threshold levels of dPUA deep in the water column, as well as the different chromatographic profiles of dPUA compared with pPUA. We propose different isomerization processes that alter the chemical structure of the released PUAs with unknown effects on their stability, biological function, and potential bioactivity.

Isolation of anti-algal substances from Cylindrotheca closterium and their inhibition activity on bloom-forming Prorocentrum donghaiense

This paper studied the allelopathic effect of Cylindrotheca closterium on the growth of Prorocentrum donghaiense, the model of harmful algal blooms in aquatic environment, by the co-culture tests and bioassay-guided fraction methods. The growth of P. donghaiense in co-cultures was observably suppressed by C. closterium, and P. donghaiense biomass in C/P = 3: 1 group increased slowly with a low growth rate of 0.18 d^-1 after 4 days. Petroleum ether (PE) extract derived from C. closterium filtrates was isolated by C18 column and the allelopathy of all isolated fractions for P. donghaiense was investigated. After 96 h cultivation, the inhibition ratio of PE-Ⅲ and PE-Ⅷ fractions on P. donghaiense could reach up to 70.2% and 64.3% at the concentration of 10-fold when compared to control, while the other fractions displayed relatively low inhibitory effects on P. donghaiense. PE-Ⅲ and PE-Ⅷ fractions also decreased the chlorophyll content and maximum quantum yield of photosystem II (Fv/Fm) of P. donghaiense cells. The activities of superoxide dismutase (SOD), one of antioxidant enzymes, reduced around 8.3% and 13.7% following exposure to 2-fold PE-Ⅲ and PE-Ⅷ, and was significantly decreased following higher exposure concentrations. After 96 h of 10-fold PE-Ⅲ and PE-Ⅷ treatments, Catalase (CAT) activity reduced to 44.86% and 46.42% of that observed in the control group. At the same time, a significant increase in malondialdehyde (MDA) contents was observed. These findings suggested that PE-Ⅲ and PE-Ⅷ fractions contained main allelochemicals and possibly acted as promising algistatic agents for emergency handling of P. donghaiense blooms.

Ectoine from Bacterial and Algal Origin Is a Compatible Solute in Microalgae

Osmoregulation in phytoplankton is attributed to several highly polar low-molecular-weight metabolites. A widely accepted model considers dimethylsulfoniopropionate (DMSP) as the most important and abundant osmotically active metabolite. Using an optimized procedure for the extraction and detection of highly polar metabolites, we expand the group of phytoplankton osmolytes by identifying ectoine in several microalgae. Ectoine is known as a bacterial compatible solute, but, to the best of our knowledge, was never considered as a phytoplankton-derived product. Given the ability of microalgae to take up zwitterions, such as DMSP, we tested the hypothesis that the algal ectoine is derived from associated bacteria. We therefore analyzed methanol extracts of xenic and axenic cultures of two different species of microalgae and could detect elevated concentrations of ectoine in those that harbor associated bacteria. However, also microalgae without an associated microbiome contain ectoine in smaller amounts, pointing towards a dual origin of this metabolite in the algae from their own biosynthesis as well as from uptake. We also tested the role of ectoine in the osmoadaptation of microalgae. In the model diatoms Thalassiosira weissflogii and Phaeodactylum tricornutum, elevated amounts of ectoine were found when cultivated in seawater with salinities of 50 PSU compared to the standard culture conditions of 35 PSU. Therefore, we add ectoine to the family of osmoadaptive metabolites in phytoplankton and prove a new, potentially synergistic metabolic interplay of bacteria and algae.

Probing the Adhesion of the Common Freshwater Diatom Nitzschia palea at Nanoscale

Freshwater biofilms play an essential ecological role, but they also adversely affect human activities through undesirable biofouling of artificial submerged structures. They form complex aggregates of microorganisms that colonize any type of substratum. In phototrophic biofilms, diatoms dominate in biomass and produce copious amount of extracellular polymeric substances (EPSs), making them efficient early colonizers. Therefore, a better understanding of diatoms adhesive properties is essential to develop new anti-biofouling strategies. In this context, we used atomic force microscopy (AFM) to decipher the topography and adhesive mechanisms of the common freshwater diatom Nitzschia palea. Images taken in physiological conditions revealed typical ultrastructural features with a few nanometers resolution. Using single-cell force spectroscopy, we showed that N. palea strongly adheres to hydrophobic surfaces as compared to hydrophilic ones. Chemical force spectroscopy with hydrophobic tips further confirmed that the adhesion is governed by surface-associated hydrophobic EPS distributed in clusters at the frustule surface, and mostly composed of (glyco)-lipids as revealed by Raman spectroscopy. Collectively, our results demonstrate that AFM-based nanoscopy, combined with Raman spectroscopy, is a powerful tool to provide new insights into the adhesion mechanisms of diatoms.

The Contribution of Carotenoids, Phenolic Compounds, and Flavonoids to the Antioxidative Properties of Marine Microalgae Isolated from Mediterranean Morocco

This study aimed to investigate the potential of four sea water microalgae, isolated and cultivated at M′diq Bay in Morocco, as a new source of natural antioxidants. These microalgae belong to different classes, including Phaedactylium tricornitum (Bacillariophyceae), Nannochloropsis gaditana (Eustigmatophyceae), Nannochloris sp (Trebouxiophyceae), and Tetraselmis suecica (Chlorodendrophycea). The antioxidant properties were screened by the use of in vitro assays, namely 2,2-difenil-1-picrylhydrazyl, Ferric reducing antioxidant power, and Ferrous ions chelating activity, and compoundidentification was carried out in methanol and acetone extracts of both dried and fresh microalgae biomass by HPLC–PDA–MS analysis. Among the investigated microalgae, Phaedactylium tricornutum was the richest one regarding its carotenoid (especially all-E-fucoxanthin) and phenolic (especially protocatechuic acid) contents, as well as antioxidant activity (65.5%), followed by Nannochloris sp, Tetraselmis suicica, and Nannochloropsis gaditana, with antioxidant activity of 56.8%, 54.9%, and 51.1%, respectively.

Effects of light and nitrogen availability on photosynthetic efficiency and fatty acid content of three original benthic diatom strains

Microalgal biotechnology has gained considerable importance in recent decades. Applications range from simple biomass production for food and animal feed to valuable products for fuel, pharmaceuticals, health, biomolecules and materials relevant to nanotechnology. There are few reports of the exploration of wider microalgae biodiversity in the literature on high value microalgal compounds, however, because it is believed that there is little to be gained in terms of biomass productivity by examining new strains. Still, without diversity, innovation in biotechnology applications is currently limited. Using microalgal diversity is a very promising way to match species and processes for a specific biotechnological application. In this context, three benthic marine diatom strains (Entomoneis paludosa NCC18.2, Nitzschia alexandrina NCC33, and Staurosira sp NCC182) were selected for their lipid production and growth capacities. Using PAM fluorometry and FTIR spectroscopy, this study investigated the impact of nitrogen repletion and depletion as well as light intensity (30, 100, and 400 μmol.photons.m^-2.s^-1) on their growth, photosynthetic performance and macromolecular content, with the aim of improving the quality of their lipid composition. Results suggest that under high light and nitrogen limitation, the photosynthetic machinery is negatively impacted, leading cells to reduce their growth and accumulate lipids and/or carbohydrates. However, increasing lipid content under stressful conditions does not increase the production of lipids of interest: PUFA, ARA and EPA production decreases. Culture conditions to optimize production of such fatty acids in these three original strains led to a balance between economic and ecophysiological constraints: low light and no nitrogen limitation led to better photosynthetic capacities associated with energy savings, and hence a more profitable approach.

Monoacylglycerides from the Diatom Skeletonema marinoi Induce Selective Cell Death in Cancer Cells

Microalgae are an excellent source of valuable compounds for nutraceutical and cosmeceutical applications. These photosynthesizing microorganisms are amenable for large-scale production, thus overcoming the bottleneck of biomass supply for chemical and activity characterization of bioactive compounds. This characteristic has recently also prompted the screening of microalgae for potential pharmaceutical applications. Here, we show that monoacylglycerides (MAGs) purified from the marine diatom Skeletonema marinoi have selective cytotoxic activity against the haematological cancer cell line U-937 and colon cancer cell line HCT-116 compared to normal MePR-2B cells. LC-MS analysis of the raw extract revealed that in their natural form, MAGs occur as 2-monoacyl derivatives and include mainly C16 and C20 analogues, but they are converted into the corresponding 1-isomers during purification processes. Pure compounds along with the synthetic 1-monoarachidonoylglycerol tested on HCT-116 and U-937 tumor cell lines induced cell death via apoptosis. The mechanism of action was investigated, and we show that it involves the induction of apoptosis through caspase 3/7 activation. These findings pave the way for the possible use of these molecules as potential anticancer agents or as precursors for the generation of new and more potent and selective compounds against tumor cells.

Yeast β-glucans and microalgal extracts modulate the immune response and gut microbiome in Senegalese sole (Solea senegalensis)

One bottleneck to sustainability of fish aquaculture is the control of infectious diseases. Current trends include the preventive application of immunostimulants and prebiotics such as polysaccharides. The present study investigated how yeast β-glucan (Y), microalgal polysaccharide-enriched extracts (MAe) and whole Phaeodactylum tricornutum cells (MA) modulated the gut microbiome and stimulated the immune system in Senegalese sole (Solea senegalensis) when administered by oral intubation. Blood, intestine and spleen samples were taken at 3 h, 24 h, 48 h and 7 days after treatment. The short-term response (within 48 h after treatment) consisted of up-regulation of il1b and irf7 expression in the gut of the Y treated group. In contrast, administration of MAe decreased expression of tnfa and the chemokine cxc10 in the gut and spleen. Both treatments down-regulated the expression of irf3 with respect to the control group. Lysozyme activity in plasma decreased at 48 h only in the MAe-treated soles. Medium-term response consisted of the up-regulation of clec and irf7 expression in the gut of the Y, MAe and MA groups and of il1b mRNAs in the spleen of the MA group compared to the control group. Microbiome analysis using 16S rDNA gene sequencing indicated that the intestine microbiome was dominated by bacteria of the Vibrio genus (>95%). All the treatments decreased the relative proportion of Vibrio in the microbiome and Y and MAe decreased and MA increased diversity. Quantitative PCR confirmed the load of bacteria of the Vibrio genus was significantly decreased and this was most pronounced in Y treated fish. These data indicate that orally administrated insoluble yeast β-glucans acted locally in the gut modulating the immune response and controlling the Vibrio abundance. In contrast, the MAe slightly reduced the Vibrio load in the intestine and caused a transient systemic anti-inflammatory response. The results indicate that these polysaccharides are a promising source of prebiotics for the sole aquaculture industry.

Verification of the Saccharina japonica Translocon Tic20 and its Localization in the Chloroplast Membrane in Diatoms

Tic20 is an important translocon protein that plays a role in protein transport in the chloroplast. The sequence of Tic20 was determined in the lower brown alga Saccharina japonica. Structural analysis of SjTic20 revealed a noncanonical structure consisting of an N-terminal non-cyanobacterium-originated EF-hand domain (a helix-loop-helix structural domain) and a C-terminal cyanobacterium-originated Tic20 domain. Subcellular localization and transmembrane analysis indicated that SjTic20 featured an "M"-type Nin-Cin-terminal orientation, with four transmembrane domains in the innermost membrane of the chloroplast in the microalga Phaeodactylum tricornutum, and the EF-hand domain was entirely extruded into the chloroplast stroma. Our study provides information on the structure, localization, and topological features of SjTic20, and further functional analysis of SjTic20 in S. japonica is needed.

Trophic importance of microphytobenthos and bacteria to meiofauna in soft-bottom intertidal habitats: A combined trophic marker approach

Meiofauna can play an important role in the carbon fluxes of soft-bottom coastal habitats. Investigation of their feeding behavior and trophic position remains challenging due to their small size. In this study, we determine and compare the food sources used by nematodes and benthic copepods by using stable isotope compositions, fatty acid profiles and compound specific isotope analyses of fatty acids in the mudflats, seagrass beds and a sandflat of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany. Suspended particulate organic matter was much more ¹³C-depleted than other food sources and meiofauna, highlighting its poor role in the different studied habitats. The very low proportions of vascular plant fatty acid markers in meiofauna demonstrated that these consumers did not rely on this food source, either fresh or detrital, even in seagrass beds. The combined use of stable isotopes and fatty acids emphasized microphytobenthos and benthic bacteria as the major food sources of nematodes and benthic copepods. Compound specific analyses of a bacteria marker confirmed that bacteria mostly used microphytobenthos as a substrate.

Harmful phytoplankton in the Beagle Channel (South America) as a potential threat to aquaculture activities

The Beagle Channel is a remote subantarctic environment where mussel aquaculture initiatives have existed since the early 1990s. Here we analyze phytoplankton biomass and composition, and the occurrence of harmful microalgae species and their toxins at three sites during the period 2015-2016. The occurrence of potentially harmful algae was observed throughout the study period, including toxigenic dinoflagellates such as Alexandrium catenella (Group I of the A. tamarense complex), A. ostenfeldii, Dinophysis acuminata, Gonyaulax spinifera, Azadinium sp., and the diatoms Pseudo-nitzschia australis and P. fraudulenta. Toxic dinoflagellates were detected in low densities whereas a Pseudo-nitzschia bloom was observed in late February. Isolates of A. catenella and P. delicatissima sensu stricto were phylogenetically characterized. The toxin profile of A. catenella was dominated by GTX4, while P. delicatissima sensu stricto showed no production of the neurotoxin domoic acid in culture conditions. The results provide base-line information for the management of harmful algal blooms in this little explored subantarctic area.

Phytosterol biosynthesis and production by diatoms (Bacillariophyceae)

Diatoms are abundant unicellular marine photosynthetic algae that have genetically diversified their physiology and metabolism while adapting to numerous environments. The metabolic repertoire of diatoms presents opportunities to characterise the biosynthesis and production of new and potentially valuable microalgal compounds, including sterols. Sterols of plant origin, known as phytosterols, have been studied for health benefits including demonstrated cholesterol-lowering properties. In this review we summarise sterol diversity, the unique metabolic features of sterol biosynthesis in diatoms, and prospects for the extraction of diatom phytosterols in comparison to existing sources. We also review biotechnological efforts to manipulate diatom biosynthesis, including culture conditions and avenues for the rational engineering of metabolism and cellular regulation.

Toxicity and Metabolic Fate of the Fungicide Carbendazim in the Typical Freshwater Diatom Navicula Species

Fungicides are frequently detected in natural water and have gained increasing attention as a result of their potential toxicity to non-target aquatic organisms. Carbendazim (CAR), a commonly used fungicide, was selected to explore its toxicity and biodegradation in a typical freshwater diatom Navicula sp. Results showed that the growth of Navicula sp. was inhibited by CAR, with a 24 h EC₅₀ value of 2.18 mg L^-1. Although the algal growth rate was recovered after 72 h of exposure, the chlorophyll a content remained significantly decreased when the concentration of CAR was above 0.5 mg L^-1. Moreover, Navicula sp. had a negative effect on the removal of CAR, and the acute toxicity by CAR was likely due to its rapid accumulation in algal cells. Mass spectrometric data revealed the transformation products of CAR from hydroxylation, methylation, decarboxylation, demethylation, and deamination in algal cultures. These results provide a better understanding of the environmental risks of CAR in water and point to the need for additional studies on the potential adverse biological effects of its intermediates.

Polyphenols obtained from Didymosphenia geminata (Lyngbye) Schmith altered the viability and proliferation of salmonids cells lines SHK-1 and CHSE-214

Didymosphenia geminata (Lyngbye) Schmidt, also referred to as Didymo, is an invasive diatom that forms nuisance mats. Since it was first reported in our country in approximately 2010, Didymo has expanded and colonized different rivers in the Zona Austral region of Chile. Its biology and effects on ecosystems are still being studied because Didymo is an invasive algal mat that forms in a range of systems from oligotrophic austral rivers to more subtropical systems. We aimed to evaluate the viability of two salmonid cell lines, CHSE-214 and SHK-1 (somatic and embryonic cell lines, respectively), in dilutions of river water alone and in river water contaminated with Didymo or polyphenols extracted from Didymo under controlled conditions. We developed an artificial river system (2 aquariums/replicate) from five different rivers from the central area (Bio-Bio) and Patagonia area (Futaleufú) of Chile to maintain Didymo in the benthic phase. The Didymo populations were maintained for six months in the water from the rivers, after which samples were obtained. Following the extraction of polyphenols from the Didymo samples maintained in the artificial rivers, toxicity assays (10 assays) were performed to determine cell viability. Our results indicated that the CHSE-214 cells were highly sensitive to increasing concentrations of Didymo extracts. We observed a 50% reduction in cell viability after 24 h of exposure to a 0.01 V/V dilution, and this treatment further reduced the proliferative capacity by 70% after 120 h. The SHK-1 cells were less responsive, showing only a 20% decrease in viability at 24 h and a lower cell proliferation rate (45%) after 120 h, which remained higher than that of the CHSE-214 cells. We conclude that certain cell types are sensitive to Didymo in rivers, suggesting that there are chronic effects on several aquatic species following exposure to these diatom substances. These effects should be further studied using this laboratory model to understand the full impact of Didymo on river ecosystems.

Phytoplankton community structure in relation to environmental factors and ecological assessment of water quality in the upper reaches of the Genhe River in the Greater Hinggan Mountains

Phytoplankton assemblages were investigated in 2015 along the seasonal changes of the Genhe River in the Greater Hinggan Mountains. The survey was performed in June (spring), August (summer), and October (autumn) at nine sampling stations to study the community composition, abundance, and biodiversity. The results showed that 61 species belonging to 16 genera were identified, including Bacillariophyta of 31 species, Dinophyta 2 species, Cyanophyta 2 species, Chlorophyta 20 species, Chrysophyta 2 species, and Cryptophyta 1 species; Besides, Bacillariophyta are dominant species. Shannon-Wiener (H') and Pielou (J') indices indicated that phytoplankton community was stable. And these two indices were significantly lower in summer than in spring and autumn. Phytoplankton abundance and biomass show significant differences in each season. The total phytoplankton abundance (1122.3 × 104 ind/L) and biomass (6.5709 mg/L) in summer are much higher than that in spring and autumn. There were few species and low abundance and biomass in the upper reaches of Genhe River; this fact can be explained by the cold climate in the Greater Higgnan Mountains region. Canonical correspondence analysis (CCA) was used to analyze the data. It revealed that Fe³⁺, Cu²⁺, pH, and water temperature (WT) were responsible for most of the variation in space in the phytoplankton community. These environmental parameters play an essential role in the community structure variation of phytoplankton in the upper reaches of Genhe River, the strong association between phytoplankton community structure and ecological factors is varied in each season.

Variation in allelopathy of extracellular compounds produced by Cylindrotheca closterium against the harmful-algal-bloom dinoflagellate Prorocentrum donghaiense

Allelopathy between algae is an ecological strategy that can facilitate or inhibit the occurrence of algal blooms. The role of allelopathic effects of marine microalgae Cylindrotheca closterium in other phytoplankton population dynamics are still limited. In the current study, the effects of cell-free filtrates of diatom Cylindrotheca closterium on two common dinoflagellates (Prorocentrum donghaiense and Prorocentrum cordatum), a chrysophyceae (Isochrysis galbana) and a diatom (Chaetoceros curvisetus) were investigated within controlled laboratory experiments. It was observed that the growth of P. donghaiense was significantly suppressed and approximately 80% cells disappeared after 8-d exposure, while the other three algae was less sensitive. P. donghaiense was very sensitive to the exudates of C. closterium from the stationary phase by comparing various percentage (10, 30, 50, 70 and 100%) of filtrates. In addition, the allelopathic effects of extracellular compounds of C. closterium extracted by three different organic solvents (ethyl acetate, chloroform and petroleum ether) on P. donghaiense were explored by determining cell density, chlorophyll content and maximum photosystem II (PSII) quantum yield (F_v/F_m). It was found that the compounds extracted by ethyl acetate and chloroform appeared to exhibit less toxicity on P. donghaiense than that of petroleum ether. The present results indicated that the allelochemicals released by C. closterium might be concentrated effectively in the petroleum ether extraction phase, which provided a new perspective for controlling the red tides of P. donghaiense in the East China Sea by means of the ecological inhibitors extracted.

Hippos (Hippopotamus amphibius): The animal silicon pump

While the importance of grasslands in terrestrial silicon (Si) cycling and fluxes to rivers is established, the influence of large grazers has not been considered. Here, we show that hippopotamuses are key actors in the savannah biogeochemical Si cycle. Through a detailed analysis of Si concentrations and stable isotope compositions in multiple ecosystem compartments of a savannah-river continuum, we constrain the processes influencing the Si flux. Hippos transport 0.4 metric tons of Si day^-1 by foraging grass on land and directly egesting in the water. As such, they bypass complex retention processes in secondary soil Si pools. By balancing internal processes of dissolution and precipitation in the river sediment, we calculate that hippos affect up to 76% of the total Si flux. This can have a large impact on downstream lake ecosystems, where Si availability directly affects primary production in the diatom-dominated phytoplankton communities.

Comparison of Diatoms and Dinoflagellates from Different Habitats as Sources of PUFAs

Recent studies have clearly shown the importance of omega-3 (ω-3) and omega-6 (ω-6) polyunsaturated fatty acids (PUFAs) for human and animal health. The long-chain eicosapentaenoic acid (EPA; 20:5ω-3) and docosahexaenoic acid (DHA; 22:6ω-3) are especially recognized for their nutritional value, and ability to alleviate many diseases in humans. So far, fish oil has been the main human source of EPA and DHA, but alternative sources are needed to satisfy the growing need for them. Therefore, we compared a fatty acid profile and content of 10 diatoms and seven dinoflagellates originating from marine, brackish and freshwater habitats. These two phytoplankton groups were chosen since they are excellent producers of EPA and DHA in aquatic food webs. Multivariate analysis revealed that, whereas the phytoplankton group (46%) explained most of the differences in the fatty acid profiles, habitat (31%) together with phytoplankton group (24%) explained differences in the fatty acid contents. In both diatoms and dinoflagellates, the total fatty acid concentrations and the ω-3 and ω-6 PUFAs were markedly higher in freshwater than in brackish or marine strains. Our results show that, even though the fatty acid profiles are genetically ordered, the fatty acid contents may vary greatly by habitat and affect the ω-3 and ω-6 availability in food webs.

A Sample Preparation Technique Using Biocompatible Composites for Biomedical Applications

Infectious diseases, especially pathogenic infections, are a growing threat to public health worldwide. Since pathogenic bacteria usually exist in complex matrices at very low concentrations, the development of technology for rapid, convenient, and biocompatible sample enrichment is essential for sensitive diagnostics. In this study, a cucurbit[6]uril (CB) supermolecular decorated amine-functionalized diatom (DA) composite was fabricated to support efficient sample enrichment and in situ nucleic acid preparation from enriched pathogens and cells. CB was introduced to enhance the rate and effectiveness of pathogen absorption using the CB-DA composite. This novel CB-DA composite achieved a capture efficiency of approximately 90% at an Escherichia coli concentration of 10⁶ CFU/mL within 3 min. Real-time PCR analyses of DNA samples recovered using the CB-DA enrichment system showed a four-fold increase in the early amplification signal strength, and this effective method for capturing nucleic acid might be useful for preparing samples for diagnostic systems.

Molecular and Morphological Toxicity of Diatom-Derived Hydroxyacid Mixtures to Sea Urchin Paracentrotus lividus Embryos

Oxylipins such as polyunsaturated aldehydes (PUAs) and hydroxyacids (HEPEs) are signaling molecules derived from the oxidation of polyunsaturated fatty acids. They are common in diatoms that constitute a major group of microalgae in freshwater and oceanic ecosystems. Although HEPEs represent the most common oxylipins produced by diatoms, little information is available on their effects on marine invertebrates, and most of the information has been obtained by testing individual HEPEs. Our previous studies reported that four hydroxyacids, i.e., 5-, 9-, 11-, and 15-HEPE, were able to induce malformations and a marked developmental delay in sea urchin Paracentrotus lividus embryos, which had not been reported for other oxylipins. Here, we tested a mixture of 5-, 9-, 11-, and 15-HEPE at different concentrations for the first time. The results showed that mixtures of HEPEs have synergistic effects that are much more severe compared to those of individual HEPEs: The HEPE mixtures induced malformations in sea urchin embryos at lower concentrations. Increasing HEPE mixture concentrations induced a marked increase in the number of delayed embryos, until all embryos were delayed at the highest concentration tested. At the molecular level, the HEPE mixtures induced variations in the expression of 50 genes involved in different functional processes, mainly down-regulating these genes at the earliest stages of embryonic development. These findings are ecologically significant, considering that during diatom blooms, sea urchins could accumulate HEPEs in concentrations comparable to those tested in the present study.

Biological monitoring in southern Africa: A review of the current status, challenges and future prospects

Biological monitoring programmes have gained popularity around the world particularly in southern Africa as they are fast, integrative and cost-effective approaches for assessing the effects of environmental stressors on aquatic ecosystems. This article reviews current efforts that have been made to use bioindicators (i.e. macroinvertebrates, diatoms and fish) in monitoring water resources and to summarise the challenges in employing these biological monitoring tools in southern Africa. In South Africa, macroinvertebrate (South African Scoring System (SASS)) and diatom based indices (e.g. South African diatom index (SADI)) have demonstrated their utility in identifying sources of impairment and determining the extent of impacts thus giving natural resource managers a scientifically defensible rationale for developing guidelines for conservation and management. Despite this advancement in South Africa, however, developing regionally appropriate quantitative tools for diagnosing ecosystem health is a pressing need for several other southern African countries. Together with sound scientific research, it is imperative for southern African countries to develop specific legislation and have mandated agencies, with proper training and funding to implement biomonitoring and bioassessments. We recommend for the advancement and adoption of biological criteria as an integrated approach to assessing the impact of human activities in riverine ecosystems of the southern African region.

UPLC⁻MS/MS Identification of Sterol Sulfates in Marine Diatoms

Diatoms are unicellular eukaryotic organisms that play a key ecological and biogeochemical role in oceans as major primary producers. Recently, these microalgae have also attracted interest as a promising source of functional products with widespread relevance. Progress in the knowledge of cell and molecular biology of diatoms is envisaged as a key step to understanding regulation of their life cycle in marine environments as well as facilitating their full and profitable exploitation by biotechnological platforms. Recently, we identified sterol sulfates (StS) as regulatory molecules of cell death in the diatom Skeletonema marinoi. As these compounds may have a general role in diatom physiology and chemical signals in aquatic systems, we investigated a suitable tool for their analysis in laboratory and field samples. Herein, we describe a sensitive, fast, and efficient ultra performance liquid chromatography–mass spectrometry (UPLC–MS) method for qualitative and quantitative analysis of StS from crude extract of diatoms and other microalgae. The method was applied to 13 different strains of our collection of marine protists. This first study suggested a species-specific distribution of StS and identified the sulfated derivatives of 24-methylene cholesterol and 24-methyl cholesterol as the most common members in diatoms.

The stresses of allelochemicals isolated from culture solution of diatom Phaeodactylum tricornutum Bohlin on growth and physiology of two marine algae

The allelopathic effects of extracts isolated from the culture filtrate of diatom Phaeodactylum triconutum Bohlin on typical marine microalgae Prorocentrum donghaiense Lu and Dunaliella salina Teodoresco were investigated by determining different physiological and biochemical parameters, such as growth rate, membrane systems and esterase activity under controlled laboratory conditions. The growth of P. donghaiense was significantly inhibited immediately after exposure to the allelochemicals, while the algae density of D. salina was less sensitive. Chlorophyll-a content, membrane systems, as well as esterase activity were simultaneously investigated by flow cytometry with particular fluorescent markers and exhibited changeable sensitivities. The results demonstrated that the membrane systems of P. donghaiense were suppressed by the allelochemicals directly, causing loss of integrity and membrane penetration. Esterase activity was the most sensitive indicator as that of P. donghaiense cells significantly increased in short time and was inhibited subsequently. However, the membrane of D. salina remained intact still after exposure to the extracts and the esterase activity was only inhibited on last day during experiment period. Membrane potential and chlorophyll-a content of the two marine algae also showed somewhat different changes, as that of P. donghaiense cells were impaired after 5 day exposure to all volume conditions while these two characteristics of D. salina was only suppressed by exposure to high volume of the allelochemicals on day 6. The present results indicated that the inhibition of culture filtrate of P. triconutum on P. donghaiense was algicidal whereas the effect on D. salina appeared to be algistatic.