Mechanism of branching morphogenesis inspired by diatom silica formation

The silica-based cell walls of diatoms are prime examples of genetically controlled, species-specific mineral architectures. The physical principles underlying morphogenesis of their hierarchically structured silica patterns are not understood, yet such insight could indicate novel routes toward synthesizing functional inorganic materials. Recent advances in imaging nascent diatom silica allow rationalizing possible mechanisms of their pattern formation. Here, we combine theory and experiments on the model diatom Thalassiosira pseudonana to put forward a minimal model of branched rib patterns-a fundamental feature of the silica cell wall. We quantitatively recapitulate the time course of rib pattern morphogenesis by accounting for silica biochemistry with autocatalytic formation of diffusible silica precursors followed by conversion into solid silica. We propose that silica deposition releases an inhibitor that slows down up-stream precursor conversion, thereby implementing a self-replicating reaction-diffusion system different from a classical Turing mechanism. The proposed mechanism highlights the role of geometrical cues for guided self-organization, rationalizing the instructive role for the single initial pattern seed known as the primary silicification site. The mechanism of branching morphogenesis that we characterize here is possibly generic and may apply also in other biological systems.

A Pseudo-nitzschia metabarcoding approach with a calibrated ITS1 reference sequence database applied in the Taiwan Strait

Pseudo-nitzschia is a cosmopolitan phytoplankton genus of which some species can form blooms and produce the neurotoxin domoic acid (DA). Identification of Pseudo-nitzschia is generally based on field material or strains followed by morphological and/or molecular characterization. However, this process is time-consuming and laborious, and can not obtain a relatively complete and reliable profile of the Pseudo-nitzschia community, because species with low abundance in the field or potentially unavailable for culturing may easily be overlooked. In the present study, specific ITS primer sets were designed and evaluated using in silico matching. The primer set ITS-84F/456R involving the complete ITS1 region was found optimal. Based on matching with a Pseudo-nitzschia ITS1 reference sequence database carefully-calibrated in this study, a metabarcoding approach using annotated amplicon sequence variants (ASV) was applied in the Taiwan Strait of the East China Sea during two cruises in the spring and summer of 2019. In total, 48 Pseudo-nitzschia species/phylotypes including 36 known and 12 novel were uncovered, and verified by haplotype networks, ITS2 secondary structure comparisons and divergence analyses. Correlation analyses revealed that temperature was a key factor affecting the seasonal variation of the Pseudo-nitzschia community. This study provides an overview of the Pseudo-nitzschia community in the Taiwan Strait, with new insights into the diversity. The developed metabarcoding approach may be used elsewhere as a standard reference for accurate annotation of Pseudo-nitzschia.

Spectral Tuning and Excitation-Energy Transfer by Unique Carotenoids in Diatom Light-Harvesting Antenna

The light-harvesting antennae of diatoms and spinach are composed of similar chromophores; however, they exhibit different absorption wavelengths. Recent advances in cryoelectron microscopy have revealed that the diatom light-harvesting antenna fucoxanthin chlorophyll a/c-binding protein (FCPII) forms a tetramer and differs from the spinach antenna in terms of the number of protomers; however, the detailed molecular mechanism remains elusive. Herein, we report the physicochemical factors contributing to the characteristic light absorption of the diatom light-harvesting antenna based on spectral calculations using an exciton model. Spectral analysis reveals the significant contribution of unique fucoxanthin molecules (fucoxanthin-S) in FCPII to the diatom-specific spectrum, and further analysis determines their essential role in excitation-energy transfer to chlorophyll. It was revealed that the specificity of these fucoxanthin-S molecules is caused by the proximity between protomers associated with the tetramerization of FCPII. The findings of this study demonstrate that diatoms employ fucoxanthin-S to harvest energy under the ocean in the absence of long-wavelength sunlight and can provide significant information about the survival strategies of photosynthetic organisms to adjust to their living environment.

Imaging and Quantitative Analysis on the Etching of Diatom Frustules via Digital Holographic Microscopy

Frustules, whose length spans from a few micrometers to more than a hundred micrometers, have been the subject of various modifications to improve their physical properties because of their complex porous silica structure. However, three-dimensional measurements of these changes can be challenging because of the complex 3D architecture and limitations of known methods. In this study, we present a new method that applies digital holographic microscopy (DHM) to analyze controlled etched frustules and observe real-time degradation of frustules at the single-cell level. Frustules obtained from Craspedostauros sp. diatoms were etched in 1 N NaOH for 5 min at 25 and 60 °C, respectively, and the frustule's valve was analyzed using DHM. DHM uses a combination of holography and tomography to reconstruct a 3D refractive index image of the frustule. Measurements of the width, volume, and surface area are achieved. Results showed that at 60 °C of etching, a significant difference with the unetched frustule was observed for all measurements but with high fluctuation values. Finally, real-time observation of the degradation of the frustule is observed when immersed in a high concentration of NaOH. This is the first time the real-time etching of the frustule is observed at the single-cell level. This research provides an easy estimation of the 3D measurements of frustules that may provide new fundamental information and applications.

Biomimetic Diatom Biosilica and Its Potential for Biomedical Applications and Prospects: A Review

Diatom biosilica is an important natural source of porous silica, with three-dimensional ordered and nanopatterned structures referred to as frustules. The unique features of diatom frustules, such as their high specific surface area, thermal stability, biocompatibility, and adaptable surface chemistry, render diatoms valuable materials for high value-added applications. These attributes make diatoms an exceptional cost-effective raw material for industrial use. The functionalization of diatom biosilica surface improves its biophysical properties and increases the potential applications. This review focuses on the potential uses of diatom biosilica including traditional approaches and recent progress in biomedical applications. Not only well-studied drug delivery systems but also promising uses on bone regeneration and wound healing are covered. Furthermore, considerable aspects and possible future directions for the use of diatom biosilica materials are proposed to develop biomedical applications and merit further exploration.

The Art of Exploring Diatom Biosilica Biomaterials: From Biofabrication Perspective

Diatom is a common single-cell microalgae with large species and huge biomass. Diatom biosilica (DB), the shell of diatom, is a natural inorganic material with a micro-nanoporous structure. Its unique hierarchical porous structure gives it great application potential in drug delivery, hemostat materials, and biosensors, etc. However, the structural diversity of DB determines its different biological functions. Screening hundreds of thousands of diatom species for structural features of DB that meet application requirements is like looking for a needle in a seaway. And the chemical modification methods lack effective means to control the micro-nanoporous structure of DB. The formation of DB is a typical biomineralization process, and its structural characteristics are affected by external environmental conditions, genes, and other factors. This allows to manipulate the micro-nanostructure of DB through biological regulation method, thereby transforming the screening mode of the structure function of DB from a needle in a seaway to biofabrication mode. This review focuses on the formation, biological modification, functional activity of DB structure, and its application in biomaterials field, providing regulatory strategies and research idea of DB from the perspective of biofabrication. It will also maximize the possibility of using DB as biological materials.

Lipidome Plasticity Enables Unusual Photosynthetic Flexibility in Arctic vs. Temperate Diatoms

The diatom lipidome actively regulates photosynthesis and displays a high degree of plasticity in response to a light environment, either directly as structural modifications of thylakoid membranes and protein-pigment complexes, or indirectly via photoprotection mechanisms that dissipate excess light energy. This acclimation is crucial to maintaining primary production in marine systems, particularly in polar environments, due to the large temporal variations in both the intensity and wavelength distributions of downwelling solar irradiance. This study investigated the hypothesis that Arctic marine diatoms uniquely modify their lipidome, including their concentration and type of pigments, in response to wavelength-specific light quality in their environment. We postulate that Arctic-adapted diatoms can adapt to regulate their lipidome to maintain growth in response to the extreme variability in photosynthetically active radiation. This was tested by comparing the untargeted lipidomic profiles, pigmentation, specific growth rates and carbon assimilation of the Arctic diatom Porosira glacialis vs. the temperate species Coscinodiscus radiatus during exponential growth under red, blue and white light. Here, we found that the chromatic wavelength influenced lipidome remodeling and growth in each strain, with P. glacialis showing effective utilization of red light coupled with increased inclusion of primary light-harvesting pigments and polar lipid classes. These results indicate a unique photoadaptation strategy that enables Arctic diatoms like P. glacialis to capitalize on a wide chromatic growth range and demonstrates the importance of active lipid regulation in the Arctic light environment.

Random mutagenesis of Phaeodactylum tricornutum using ultraviolet, chemical, and X-radiation demonstrates the need for temporal analysis of phenotype stability

We investigated two non-ionising mutagens in the form of ultraviolet radiation (UV) and ethyl methanosulfonate (EMS) and an ionising mutagen (X-ray) as methods to increase fucoxanthin content in the model diatom Phaeodactylum tricornutum. We implemented an ultra-high throughput method using fluorescence-activated cell sorting (FACS) and live culture spectral deconvolution for isolation and screening of potential pigment mutants, and assessed phenotype stability by measuring pigment content over 6 months using high-performance liquid chromatography (HPLC) to investigate the viability of long-term mutants. Both UV and EMS resulted in significantly higher fucoxanthin within the 6 month period after treatment, likely as a result of phenotype instability. A maximum fucoxanthin content of 135 ± 10% wild-type found in the EMS strain, a 35% increase. We found mutants generated using all methods underwent reversion to the wild-type phenotype within a 6 month time period. X-ray treatments produced a consistently unstable phenotype even at the maximum treatment of 1000 Grays, while a UV mutant and an EMS mutant reverted to wild-type after 4 months and 6 months, respectively, despite showing previously higher fucoxanthin than wild-type. This work provides new insights into key areas of microalgal biotechnology, by (i) demonstrating the use of an ionising mutagen (X-ray) on a biotechnologically relevant microalga, and by (ii) introducing temporal analysis of mutants which has substantial implications for strain creation and utility for industrial applications.

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

The hierarchical porous structures of diatom biosilica-based hemostat: From selective adsorption to rapid hemostasis

Here, we developed a Ca2+ modified diatom biosilica-based hemostat (DBp-Ca2+) with a full scale hierarchical porous structure (pore sizes range from micrometers to nanometers). The unique porous size in stepped arrangement of DBp-Ca2+give it selective adsorption capacity during coagulation process, resulted in rapid hemorrhage control. Based on in vitro and in vivo studies, it was confirmed that the primary micropores of DBp-Ca2+gave it high porosity to hold water (water absorption: 78.46 ± 1.12 %) and protein (protein absorption: 83.7 ± 1.33 mg/g). Its secondary mesopores to macropores could reduce of water diffusion length to accelerate blood exchange (complete within 300 ms). The tertiary stacking pores of DBp-Ca2+ could absorb platelets and erythrocytes to reduce more than 50 % of thrombosis time, and provided enough contact between Ca active site and coagulation factors for triggering clotting cascade reaction. This work not only developed a novel DBs based hemostat with efficient hemorrhage control, but also provided new insights to study procoagulant mechanism of inorganic hemostat with hierarchical porous structure from selective adsorption to rapid hemostasis.

Polyunsaturated Aldehydes Profile in the Diatom Cyclotella cryptica Is Sensitive to Changes in Its Phycosphere Bacterial Assemblages

Diatoms are responsible for the fixation of ca. 20% of the global CO2 and live associated with bacteria that utilize the organic substances produced by them. Current research trends in marine microbial ecology show which diatom and bacteria interact mediated through the production and exchange of infochemicals. Polyunsaturated aldehydes (PUA) are organic molecules released by diatoms that are considered to have infochemical properties. In this work, we investigated the possible role of PUA as a mediator in diatom-bacteria interactions. To this end, we compare the PUA profile of a newly isolated oceanic PUA producer diatom, Cyclotella cryptica, co-cultured with and without associated bacteria at two phosphate availability conditions. We found that the PUA profile of C. cryptica cultured axenically was different than its profile when it was co-cultured with autochthonous (naturally associated) and non-autochthonous bacteria (unnaturally inoculated). We also observed that bacterial presence significantly enhanced diatom growth and that C. cryptica modulated the percentage of released PUA in response to the presence of bacteria, also depending on the consortium type. Based on our results, we propose that this diatom could use released PUA as a specific organic matter sign to attract beneficial bacteria for constructing its own phycosphere, for more beneficial growth.

Description and Characterization of the Odontella aurita OAOSH22, a Marine Diatom Rich in Eicosapentaenoic Acid and Fucoxanthin, Isolated from Osan Harbor, Korea

Third-generation biomass production utilizing microalgae exhibits sustainable and environmentally friendly attributes, along with significant potential as a source of physiologically active compounds. However, the process of screening and localizing strains that are capable of producing high-value-added substances necessitates a significant amount of effort. In the present study, we have successfully isolated the indigenous marine diatom Odontella aurita OAOSH22 from the east coast of Korea. Afterwards, comprehensive analysis was conducted on its morphological, molecular, and biochemical characteristics. In addition, a series of experiments was conducted to analyze the effects of various environmental factors that should be considered during cultivation, such as water temperature, salinity, irradiance, and nutrients (particularly nitrate, silicate, phosphate, and iron). The morphological characteristics of the isolate were observed using optical and electron microscopes, and it exhibited features typical of O. aurita. Additionally, the molecular phylogenetic inference derived from the sequence of the small-subunit 18S rDNA confirmed the classification of the microalgal strain as O. aurita. This isolate has been confirmed to contain 7.1 mg g-1 dry cell weight (DCW) of fucoxanthin, a powerful antioxidant substance. In addition, this isolate contains 11.1 mg g-1 DCW of eicosapentaenoic acid (EPA), which is one of the nutritionally essential polyunsaturated fatty acids. Therefore, this indigenous isolate exhibits significant potential as a valuable source of bioactive substances for various bio-industrial applications.

Structure of a diatom photosystem II supercomplex containing a member of Lhcx family and dimeric FCPII

Diatoms rely on fucoxanthin chlorophyll a/c-binding proteins (FCPs) for their great success in oceans, which have a great diversity in their pigment, protein compositions, and subunit organizations. We report a unique structure of photosystem II (PSII)-FCPII supercomplex from Thalassiosira pseudonana at 2.68-Å resolution by cryo-electron microscopy. FCPIIs within this PSII-FCPII supercomplex exist in dimers and monomers, and a homodimer and a heterodimer were found to bind to a PSII core. The FCPII homodimer is formed by Lhcf7 and associates with PSII through an Lhcx family antenna Lhcx6_1, whereas the heterodimer is formed by Lhcf6 and Lhcf11 and connects to the core together with an Lhcf5 monomer through Lhca2 monomer. An extended pigment network consisting of diatoxanthins, diadinoxanthins, fucoxanthins, and chlorophylls a/c is revealed, which functions in efficient light harvesting, energy transfer, and dissipation. These results provide a structural basis for revealing the energy transfer and dissipation mechanisms and also for the structural diversity of FCP antennas in diatoms.

Probing the Fucoxanthin-Chlorophyll a/c-Binding Proteins (FCPs) of the Marine Diatom Fragilariopsis sp. by Resonance Raman Spectroscopy

We report resonance Raman spectra of the light-harvesting fucoxanthin-chlorophyll a/c-binding proteins (FCPs) of marine diatom Fragilariopsis sp. The Raman shifts in the 15N-isotope-enriched diatom provide the first spectroscopic evidence for the characterization of the Ca-N marker bands and, thus, of the penta- and hexacoordinated states of chlorophylls a/c in the FCPs. Under 405 and 442 nm Raman excitations, all of the marker bands of Chl a/c are observed and the isotope-based assignments provide new information concerning the structure of Chls a/c in the FCPs and their interactions with the protein environment. Therefore, the Raman spectrum at 405 nm originates from the π-π* transitions of Chl a/c and not from a different, non π-π* electronic transition, as previously reported (BBA Bioenergetics, 2010, 1797, 1647-1656). Based on the 15N isotope shifts of the Ca-N and in conjunction with other marker bands, two distinct conformations of five- and six-coordinated Chl a and Chl c are observed. In addition, two keto carbonyls were observed at 1679 (strong H-bonded) and 1691 cm-1 (weak H-bonded) in both the 405 and 442 nm Raman spectra, respectively. Collectively, the results provide solid evidence of the nature of the vibrational modes of the active Chl a/c photosynthetic pigments in the FCPs.

Bubble-free diatoms polymerase chain reaction

Polymerase chain reaction (PCR) in small fluidic systems not only improves speed and sensitivity of deoxyribonucleic acid (DNA) amplification but also achieves high-throughput quantitative analyses. However, air bubble trapping and growth during PCR has been considered as a critical problem since it causes the failure of DNA amplification. Here we report bubble-free diatom PCR by exploiting a hierarchically porous silica structure of single-celled algae. We show that femtoliters of PCR solution can be spontaneously loaded into the diatom interior without air bubble trapping due to the surface hydrophilicity and pore structure of the diatom. We discover that a large pressure gradient between air bubbles and nanopores rapidly removes residual air bubbles through the periodically arrayed nanopores during thermal cycling. We demonstrate the DNA amplification by diatom PCR without air bubble trapping and growth. Finally, we successfully detect DNA fragments of SARS-CoV-2 with as low as 10 copies/μl by devising a microfluidic device integrated with diatoms assembly. We believe that our work can be applied to many PCR applications for innovative molecular diagnostics and provides new opportunities for naturally abundant diatoms to create innovative biomaterials in real-world applications.

A novel effective bio-originated methylene blue adsorbent: the porous biosilica from three marine diatom strains of Nanofrustulum spp. (Bacillariophyta)

In the present paper, for the first time the ability of the porous biosilica originated from three marine diatom strains of 'Nanofrustulum spp.' viz. N. wachnickianum (SZCZCH193), N. shiloi (SZCZM1342), N. cf. shiloi (SZCZP1809), to eliminate MB from aqueous solutions was investigated. The highest biomass was achieved under silicate enrichment for N. wachnickianum and N. shiloi (0.98 g L-1 DW and 0.93 g L-1 DW respectively), and under 15 °C for N. cf. shiloi (2.2 g L-1 DW). The siliceous skeletons of the strains were purified with hydrogen peroxide and characterized by SEM, EDS, the N2 adsorption/desorption, XRD, TGA, and ATR-FTIR. The porous biosilica (20 mg DW) obtained from the strains i.e. SZCZCH193, SZCZM1342, SZCZP1809, showed efficiency in 77.6%, 96.8%, and 98.1% of 14 mg L-1 MB removal under pH 7 for 180 min, and the maximum adsorption capacity was calculated as 8.39, 19.02, and 15.17 mg g-1, respectively. Additionally, it was possible to increase the MB removal efficiency in alkaline (pH = 11) conditions up to 99.08% for SZCZP1809 after 120 min. Modelling revealed that the adsorption of MB follows Pseudo-first order, Bangham's pore diffusion and Sips isotherm models.

Diatom-inspired stiffness optimization for plates and cellular solids

Diatoms, a class of aquatic autotrophic microorganisms, are characterized by silicified exoskeletons with highly complex architectures. These morphologies have been shaped by the selection pressure that the organisms have been subjected to during their evolutionary history. Two properties which are highly likely to have contributed to the evolutionary success of current diatom species are lightweightness and structural strength. Thousands of diatom species are present in water bodies today, and although each has its unique shell architecture, a strategy that is common across species is the uneven and gradient solid material distribution across their shells. The aim of this study is to present and evaluate two novel structural optimization workflows inspired by material grading strategies in diatoms. The first workflow mimics theAuliscus intermidusdiatoms' surface thickening strategy and generates continuous sheet structures with optimal boundaries and local sheet thickness distributions when applied to plate models subjected to in-plane boundary conditions. The second workflow mimics theTriceratium sp.diatoms' cellular solid grading strategy, and produces 3D cellular solids with optimal boundaries and local parameter distributions. Both methods are evaluated through sample load cases, and prove to be highly efficient in transforming optimization solutions with non-binary relative density distributions into highly performing 3D models.

Ecological distribution of modern diatom in peatlands in the northern Greater Khingan Mountains and its environmental implications

Relationships between diatom assemblages and environmental variables in peatlands of the northern Greater Khingan Mountains are helpful for understanding the indicative significance of diatoms to environment changes, and potentially provide a reference for environmental monitoring and paleoenvironment reconstruction in the edge of monsoon region. In this study, we analyzed modern diatom assemblages and their relationships with environment factors in 30 surface samples from shrubby-herbaceous and herbaceous peatlands based on ordination analysis. Benthic and epiphytic Pennatae diatoms are mainly ecological types, whereas planktonic Centricae diatoms are relatively fewer. The most diverse genera are Pinnularia and Eunotia. Eunotia paludosa and Achnanthidium minutissimum dominated in shrubby-herbaceous peatlands, while Navicula minima and Fragilaria capucina dominated in herbaceous peatlands. The diatom community structures are different in different vegetation types and the diatom species diversity in herbaceous peatlands is higher than that in shrubby-herbaceous peatlands. COD_Mn and pH are the most important environmental factors affecting diatom species composition and diversity. Eunotia bilunaris, Eunotia mucophila, and Eunotia paludosa can be used as indicators of acidic water environments. Caloneis silicula, Fragilaria capucina, Hantzschia amphioxys, and Navicula radiosa can be applied to indicate the weak alkaline conditions. Eunotia bilunaris and Eunotia paludosa can indicate low conductivity, while Sellaphora pupula indicates the medium-high conductivity. Fragilaria capucina and Navicula radiosa can indicate oligotrophic habitats.

Silicon Limitation Impairs the Tolerance of Marine Diatoms to Pristine Microplastics

Marine diatoms are currently facing increasing threats from microplastic (MP) pollution that is intertwined with the disturbed nutrient stoichiometry in seawater. The effects of nutrient imbalances such as silicon (Si) limitation on the interactions between diatoms and MPs remain poorly understood. In contrast to previous studies which mainly focused on MP toxicity, this study emphasizes how Si availability affects nano-scale interactions between pristine polystyrene MPs and diatom surfaces. Results showed that Si-starved cells were less tolerant to MP toxicity than the Si-enriched counterparts. Si limitation significantly changed the configuration and chemical composition of the perforated frustules, forming less negatively charged, more adhesive, and mechanically weaker cells. All of these changes facilitated the adsorption and hetero-aggregation between the diatom cells and MPs and compromised the diatoms' resistance to MP attack. Our study provides novel insights into the effects of pristine MPs in the marine environment under the context of dynamic nutrient conditions.

Efficient removal of Cd2+ by diatom frustules self-modified in situ with intercellular organic components

The organic modification of three-dimensional porous diatom frustules (biosilica) and their fossils (diatomite) is promising in heavy metal adsorption. However, the preparation of such materials involves complex processes, high costs, and environmental hazards. In this study, organic-biosilica composites based on in situ self-modification of diatoms were prepared by freeze-drying pretreatment. Freeze-drying resulted in the release of the intercellular organic components of diatoms, followed by loading on the surface of their diatom frustules. The bio-adsorbent exhibits outstanding Cd²⁺ adsorption capacity (up to 220.3 mg/g). The adsorption isotherms fitted the Langmuir model and the maximum adsorption capacity was 4 times greater than that of diatom biosilica (54.1 mg/g). The adsorption kinetics of Cd²⁺ was adequately described by a pseudo-second-order model and reached equilibrium within 30 min. By combining focused ion beam thinning with transmission electron microscopy-energy dispersive X-ray spectroscopy, the internal structure of the composite and the Cd²⁺ distribution were investigated. The results showed that the organic matter of the composite adsorbed approximately 10 times more Cd²⁺ than inorganic biosilica. The adsorption mechanism was dominated by complexation between the abundant organic functional groups (amide, carboxyl, and amino groups) on the surfaces of composite and Cd²⁺. The bio-adsorbent was demonstrated to have wide applicability in the presence of competitive cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) and under a wide range of pH (3-10) conditions. Thus, the self-modification of diatoms offers a promising organic-inorganic composite for heavy metal remediation.

Mechanism of Absorption Wavelength Shift Depending on the Protonation State of the Acrylate Group in Chlorophyll c

Diatoms can use light in the blue-green region because they have chlorophyll c (Chlc) in light-harvesting antenna proteins, fucoxanthin and chlorophyll a/c-binding protein (FCP). Chlc has a protonatable acrylate group (-CH═CH-COOH/COO-) conjugated to the porphyrin ring. As the absorption wavelength of Chlc changes upon the protonation of the acrylate group, Chlc is a candidate component that is responsible for photoprotection in diatoms, which switches the FCP function between light-harvesting and energy-dissipation modes depending on the light intensity. Here, we investigate the mechanism by which the absorption wavelength of Chlc changes owing to the change in the protonation state of the acrylate group, using a quantum mechanical/molecular mechanical approach. The calculated absorption wavelength of the Soret band of protonated Chlc is ∼25 nm longer than that of deprotonated Chlc, which is due to the delocalization of the lowest (LUMO) and second lowest (LUMO+1) unoccupied molecular orbitals toward the acrylate group. These results suggest that in FCP, the decrease in pH on the lumenal side under high-light conditions leads to protonation of Chlc and thereby a red shift in the absorption wavelength.

A new pathway for anaerobic biotransformation of marine toxin domoic acid

Domoic acid (DA) is a harmful algal toxin produced by marine diatom Pseudo-nitzschia and seriously threatens ecosystem and human health. However, the current knowledge on its biotransformation behavior in coastal anaerobic environment is lacking. This study investigated the anaerobic biotransformation of DA by a new marine consortium GH1. The results demonstrated that 90% of DA (1 mg L^-1) was cometabolically biotransformed under sulfate-reducing condition. A new anaerobic biotransformation pathway involving DA hydration, dehydrogenation, and C-C bond cleavage was proposed, where the conjugated double-bond of DA was interrupted, resulting in the corresponding alcohols and ketones, subsequently cleaved hydrolytically, and yielding the lower molecular weight products. Desulfovibrio and Clostridiales were markedly enriched in the anaerobic biotransformation of DA, which might jointly contribute to the elevated bacterial consortium resistance and degradation to DA. This study could deepen understanding of behavior and fate for DA in marine environments.

Response mechanism of microbial community during anaerobic biotransformation of marine toxin domoic acid

Domoic acid (DA) is a potent neurotoxin produced by toxigenic Pseudo-nitzschia blooms and quickly transfers to the benthic anaerobic environment by marine snow particles. DA anaerobic biotransformation is driven by microbial interactions, in which trace amounts of DA can cause physiological stress in marine microorganisms. However, the underlying response mechanisms of microbial community to DA stress remain unclear. In this study, we utilized an anaerobic marine DA-degrading consortium GLY (using glycine as co-substrate) to systematically investigate the global response mechanisms of microbial community during DA anaerobic biotransformation.16S rRNA gene sequencing and metatranscriptomic analyses were applied to measure microbial community structure, function and metabolic responses. Results showed that DA stress markedly changed the composition of main species, with increased levels of Firmicutes and decreased levels of Proteobacteria, Cyanobacteria, Bacteroidetes and Actinobacteria. Several genera of tolerated bacteria (Bacillus and Solibacillus) were increased, while, Stenotrophomonas, Sphingomonas and Acinetobacter were decreased. Metatranscriptomic analyses indicated that DA stimulated the expression of quorum sensing, extracellular polymeric substance (EPS) production, sporulation, membrane transporters, bacterial chemotaxis, flagellar assembly and ribosome protection in community, promoting bacterial adaptation ability under DA stress. Moreover, amino acid metabolism, carbohydrate metabolism and lipid metabolism were modulated during DA anaerobic biotransformation to reduce metabolic burden, increase metabolic demands for EPS production and DA degradation. This study provides the new insights into response of microbial community to DA stress and its potential impact on benthic microorganisms in marine environments.

Ultrastructure of setae of a planktonic diatom, Chaetoceros coarctatus

Silica frustules of most planktonic diatoms have many shallow holes in which the length (L) is smaller than the width (W). The present study focuses on a silica ultrastructure of setae of a planktonic diatom having deep (L/W > 1) holes. Here, we characterized microscopically patterned nanoholes on the silica walls of thick, robust, and hollow setae of a colony of Chaetoceros coarctatus. Basically, tetragonal poroid arrangements with and without a costa pattern are observed on the inner and outer surfaces, respectively, for three kinds of curving hollow setae attached to the anterior, intercalary, and posterior parts of the colony. The seta structures including specific poroid arrangements and continuity of deep nanoholes depend on the location. The deep nanoholes ∼90 nm wide are elongated from 150 to 1500 nm (L/W ∼17) with an increase in the wall thickness of the polygonal tubes of the setae. The inside poroid array, with a period of 190 nm in the extension direction of setae, is lined by parallel plates of the costae. However, the poroid arrangement on the outer surface is disordered, with several holes obstructed with increasing wall thickness of the posterior terminal setae. According to the movement of a colony in a fluid microchannel, the thick curving terminal setae is suggested to involve attitude control and mechanical protection. Using an optical simulation, the patterned deep through-holes on the intercalary setae were suggested to contribute anti-reflection of blue light in the wavelength range of 400 to 500 nm for the promotion of photosynthesis in seawater.

Toxicity of the Diatom Genus Pseudo-nitzschia (Bacillariophyceae): Insights from Toxicity Tests and Genetic Screening in the Northern Adriatic Sea

Diatoms of the genus Pseudo-nitzschia H.Peragallo are known to produce domoic acid (DA), a toxin involved in amnesic shellfish poisoning (ASP). Strains of the same species are often classified as both toxic and nontoxic, and it is largely unknown whether this difference is also genetic. In the Northern Adriatic Sea, there are virtually no cases of ASP, but DA occasionally occurs in shellfish samples. So far, three species-P. delicatissima (Cleve) Heiden, P. multistriata (H. Takano) H. Takano, and P. calliantha Lundholm, Moestrup, & Hasle-have been identified as producers of DA in the Adriatic Sea. By means of enzme-linked immunosorbent assay (ELISA), high-performance liquid chromatography with UV and visible spectrum detection (HPLC-UV/VIS), and liquid chromatography with tandem mass spectrometry (LC-MS/MS), we reconfirmed the presence of DA in P. multistriata and P. delicatissima and detect for the first time in the Adriatic Sea DA in P. galaxiae Lundholm, & Moestrup. Furthermore, we attempted to answer the question of the distribution of DA production among Pseudo-nitzschia species and strains by sequencing the internal transcribed spacer (ITS) phylogenetic marker and the dabA DA biosynthesis gene and coupling this with toxicity data. Results show that all subclades of the Pseudo-nitzschia genus contain toxic species and that toxicity appears to be strain dependent, often with geographic partitioning. Amplification of dabA was successful only in toxic strains of P. multistriata and the presence of the genetic architecture for DA production in non-toxic strains was thus not confirmed.

Identification of sequence motifs in Lhcx proteins that confer qE-based photoprotection in the diatom Phaeodactylum tricornutum

Photosynthetic organisms in nature often experience light fluctuations. While low light conditions limit the energy uptake by algae, light absorption exceeding the maximal rate of photosynthesis may go along with enhanced formation of potentially toxic reactive oxygen species. To preempt high light-induced photodamage, photosynthetic organisms evolved numerous photoprotective mechanisms. Among these, energy-dependent fluorescence quenching (qE) provides a rapid mechanism to dissipate thermally the excessively absorbed energy. Diatoms thrive in all aquatic environments and thus belong to the most important primary producers on earth. qE in diatoms is provided by a concerted action of Lhcx proteins and the xanthophyll cycle pigment diatoxanthin. While the exact Lhcx activation mechanism of diatom qE is unknown, two lumen-exposed acidic amino acids within Lhcx proteins were proposed to function as regulatory switches upon light-induced lumenal acidification. By introducing a modified Lhcx1 lacking these amino acids into a Phaeodactylum tricornutum Lhcx1-null qE knockout line, we demonstrate that qE is unaffected by these two amino acids. Based on sequence comparisons with Lhcx4, being incapable of providing qE, we perform domain swap experiments of Lhcx4 with Lhcx1 and identify two peptide motifs involved in conferring qE. Within one of these motifs, we identify a tryptophan residue with a major influence on qE establishment. This tryptophan residue is located in close proximity to the diadinoxanthin/diatoxanthin-binding site based on the recently revealed diatom Lhc crystal structure. Our findings provide a structural explanation for the intimate link of Lhcx and diatoxanthin in providing qE in diatoms.

Variability of Omega-3/6 Fatty Acid Obtained Through Extraction-Transesterification Processes from Phaeodactylum tricornutum

The effect of direct transesterification methods on the omega-3/6 composition of extracts from Phaeodactylum tricornutum was studied. The aim of this work was to identify an extraction method which allowed to obtain the most suitable profile of fatty acids in terms of its potential benefits to health, particularly if further used in the food industry. Seven methods using acids, alkalis, and heterogeneous-catalysts, (namely methods from 1 to 7, abbreviated as M1-M7) were performed to determine α-linolenic (ALA), linoleic (LA), docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. The composition of fatty acids was in all cases characterized by the major abundance of palmitic (23.95-34.08%), palmitoleic (30.94-35.56%), oleic acids (3.00-7.41%), and EPA (0.5-6.45%). Unsaturated fatty acids extraction yield was higher with a two-step transesterification process (M6, 63.65%). The total fatty acid methyl ester content (FAME) obtained with acid-transesterification (M1) reached about 21% wt, and 60% w/w total lipids. ALA higher relative content (ALA/LA ratio) was obtained when a lipid pre-extraction step was performed prior to acid-catalysis (M4). The transesterification method based on alkali-catalyst (M3, KOH catalyst) led to obtain higher DHA relative contents (DHA/EPA ratio up to 0.11), although its FAME content was 3.75-fold lower than that obtained with acid-transesterification (M1). Overall, this study shows that direct transesterification with alkali-catalyst (M3) improves the determination of PUFA content from the diatom through a more efficient transesterification-based extraction process, and thus allow to assess the value of the biomass more accurately for application in the food industry.

Structural Contour Map of the Iota Carbonic Anhydrase from the Diatom Thalassiosira pseudonana Using a Multiprong Approach

Carbonic anhydrases (CAs) are a family of ubiquitous enzymes that catalyze the interconversion of CO₂ and HCO₃⁻. The “iota” class (ι-CA) was first found in the marine diatom Thalassiosira pseudonana (tpι-CA) and is widespread among photosynthetic microalgae and prokaryotes. The ι-CA has a domain COG4875 (or COG4337) that can be repeated from one to several times and resembles a calcium–calmodulin protein kinase II association domain (CaMKII-AD). The crystal structure of this domain in the ι-CA from a cyanobacterium and a chlorarachniophyte has been recently determined. However, the three-dimensional organization of the four domain-containing tpι-CA is unknown. Using biophysical techniques and 3-D modeling, we show that the homotetrameric tpι-CA in solution has a flat “drone-like” shape with a core formed by the association of the first two domains of each monomer, and four protruding arms formed by domains 3 and 4. We also observe that the short linker between domains 3 and 4 in each monomer confers high flexibility, allowing for different conformations to be adopted. We propose the possible 3-D structure of a truncated tpι-CA containing fewer domain repeats using experimental data and discuss the implications of this atypical shape on the activity and metal coordination of the ι-CA.

Impact of organic carbon acquisition on growth and functional biomolecule production in diatoms

Diatoms are unicellular photosynthetic protists which constitute one of the most successful microalgae contributing enormously to global primary productivity and nutrient cycles in marine and freshwater habitats. Though they possess the ability to biosynthesize high value compounds like eicosatetraenoic acid (EPA), fucoxanthin (Fx) and chrysolaminarin (Chrl) the major bottle neck in commercialization is their inability to attain high density growth. However, their unique potential of acquiring diverse carbon sources via varied mechanisms enables them to adapt and grow under phototrophic, mixotrophic as well as heterotrophic modes. Growth on organic carbon substrates promotes higher biomass, lipid, and carbohydrate productivity, which further triggers the yield of various biomolecules. Since, the current mass culture practices primarily employ open pond and tubular photobioreactors for phototrophic growth, they become cost intensive and economically non-viable. Therefore, in this review we attempt to explore and compare the mechanisms involved in organic carbon acquisition in diatoms and its implications on mixotrophic and heterotrophic growth and biomolecule production and validate how these strategies could pave a way for future exploration and establishment of sustainable diatom biorefineries for novel biomolecules.

A composite sponge based on alkylated chitosan and diatom-biosilica for rapid hemostasis

Rapid control of bleeding is of great significance in military trauma and traffic accidents. In this study, alkylated chitosan (AC) and diatom biosilica (DB) were combined to develop a safe and effective hemostatic composite sponge (AC-DB sponge) for hemorrhage control. Due to the procoagulant chemical structure of AC-DB sponge, it exhibited rapid hemostatic ability in vitro (clotting time was shortened by 78% than that of control group), with favorable biocompatibility (hemolysis ratio < 5%, no cytotoxicity). The strong interface effect between AC-DB sponge and blood induced the erythrocyte and platelets activation, deformation and aggregation, intrinsic coagulation pathway activation, resulting in significant coagulation acceleration. AC-DB sponge had excellent performance in in vivo assessments with shortest clotting time (106.2 s) and minimal blood loss (328.5 mg). All above results proved that AC-DB sponge had great potential to be a safe and rapid hemostatic material.

Influence of Algae Supplementation on the Concentration of Glutathione and the Activity of Glutathione Enzymes in the Mice Liver and Kidney

Algae are potential and natural source of long-chain polyunsaturated fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The diatom Pinnularia borealis accumulates high levels of EPA and may be considered as a source for commercial production of dietary supplements. In this study we asked the question whether diet supplementation with P. borealis may augment antioxidant defense and ameliorate risk factors for cardiovascular diseases. We fed mice (Mus musculus) with lyophilized diatom solutions of different concentrations (1%, 3%, and 5%) for 7 days. Then we measured glutathione content and the activity of glutathione redox system enzymes, total cholesterol and triacylglycerol concentrations, and malondialdehyde concentration in the liver and kidney. We found that cholesterol and triacylglycerol concentrations in the liver and kidneys were the lowest in mice who were fed with the highest concentration of Pinnularia borealis, suggesting protective properties of algae. Additionally, the lowest concentration of Pinnularia borealis was sufficient to improve antioxidant capacity. Our results suggest that P. borealis may be used as a source for dietary supplements rich in EPA, but the amount supplied to the organism should be limited.

In vitro intestinal digestion of lipids from the marine diatom Porosira glacialis compared to commercial LC n-3 PUFA products

Marine sources of long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are in high demand for use in health supplements. Mass cultivated marine microalgae is a promising and sustainable source of LC n-3 PUFA, which relieves pressure on natural fish stocks. The lipid class profile from cultivated photosynthetic algae differ from the marine organisms currently used for the production of LC n-3 PUFA. The objective of this study was to compare in vitro intestinal digestion of oil extracted from the cold-adapted marine diatom Porosira glacialis with commercially available LC n-3 PUFA supplements; cod liver oil, krill oil, ethyl ester concentrate, and oil from the copepod Calanus finmarchicus (Calanus® oil). The changes in the free fatty acids and neutral and polar lipids during the enzymatic hydrolysis were characterized by liquid and gas chromatography. In Calanus® oil and the Ethyl ester concentrate, the free fatty acids increased very little (4.0 and 4.6%, respectively) during digestion. In comparison, free fatty acids in Krill oil and P. glacialis oil increased by 14.7 and 17.0%, respectively. Cod liver oil had the highest increase (28.2%) in free fatty acids during the digestion. Monounsaturated and saturated fatty acids were more easily released than polyunsaturated fatty acids in all five oils.

Diatom Silica/Polysaccharide Elastomeric Hydrogels: Adhesion and Interlocking Synergy

The addition of particles during the sol-to-gel conversion process generally enhances the mechanical properties of the resulting hydrogels. However, the impact of the addition of porous particles during such a process remains an open question. Herein, we report hydrogel-to-elastomer conversions by natural porous particles called diatom frustule silica, namely, Melosira nummuloides. The surface pores provide mechanical interlocking points for polymers that are reinforced by gelation. The most critical aspect when choosing polymeric materials is the presence of water-resistant adhesion moieties, such as catechol, along a polymer chain, such as chitosan. Without catechol, no sol-to-gel conversion is observed; thus, no elastomeric hydrogel is produced. The resulting hybrid gel reveals reversible compressibility up to a 60% strain and high stretchability even up to ∼400% in area. Further, in vivo study demonstrates that the hybrid composite gel can be used as a therapeutic for pressure-induced ulcers. The synergy of chemical adhesion and physical chain entanglement via pores provides a way to fabricate a new class of 100% water-based elastomeric materials.

Amphora algae with low-level ionizing radiation exposure ameliorate D-galactosamine-induced inflammatory impairment in rat kidney

d-Galactosamine (d-GalN) is a well-known toxin that causes many metabolic and morphological abnormalities resulting in advanced renal failure and liver damage. Occupational exposure to low-level ionizing radiation (<1 Gy) was shown to enhance cell protection via attenuating an established inflammatory process. The present study was therefore aimed to investigate the protective impact of Amphora coffaeiformis extract and low dose gamma radiation against d-GalN induced renal damage in rats. Forty-eight adult male Swiss albino rats were distributed equally into eight groups. The measurements included antioxidants activities (superoxide dismutase, catalase and glutathione peroxidase) as well as lipid peroxidation level in kidney tissue. Also, kidney function tests and inflammatory markers (tumor necrosis factor alpha and nuclear factor kappa-light-chain-enhancer of activated B cells) were measured. Additionally, relative quantification of kidney nuclear factor erythroid 2-related factor 2 (Nrf-2) gene was estimated. Histopathological examination was also performed in kidney tissue. The results revealed decreases in antioxidant activities and downregulation of Nrf-2 expression accompanied by increases in lipid peroxidation level, kidney function tests and inflammatory markers in d-GaIN group. The treatment with Amphora algal extract and low dose gamma radiation ameliorated the previous measurements which were harmony with histopathological findings. In conclusion, A coffaeiformis extract and low dose gamma radiation provided marked functional and histological effects in the treating acute renal damage induced by d-GalN in rats.

Therapeutic attributes and applied aspects of biological macromolecules (polypeptides, fucoxanthin, sterols, fatty acids, polysaccharides, and polyphenols) from diatoms - A review

Diatoms are ubiquitous, biologically widespread, and have global significance due to their unique silica cell wall composition and noteworthy applied aspects. Diatoms are being extensively exploited for environmental monitoring, reconstruction, and stratigraphic correlation. However, considering all the rich elements of diatoms biology, the current literature lacks sufficient information on the therapeutic attributes and applied aspects of biological macromolecules from diatoms, hampering added advances in all aspects of diatom biology. Diatoms offer numerous high-value compounds, such as fatty acids, polysaccharides, polypeptides, pigments, and polyphenols. Diatoms with a high content of PUFA's are targets of transformation into high-value products through microalgal technologies due to their wide application and growing market as nutraceuticals and food supplements. Diatoms are renewable biomaterial, which can be used to develop drug delivery systems due to biocompatibility, surface area, cost-effective ratio, and ease in surface modifications. Innovative approaches are needed to envisage cost-effective ways for the isolation of bioactive compounds, enhance productivity, and elucidate the detailed mechanism of action. This review spotlights the notable applications of diatoms and their biologically active constituents, such as fucoxanthin and omega 3 fatty acids, among others with unique structural and functional entities.

Cell carbon content and biomass assessments of dinoflagellates and diatoms in the oceanic ecosystem of the Southern Gulf of Mexico

This study assessed the cell carbon content and biomass for genera of dinoflagellates and diatoms in the oceanic ecosystem of the Southern Gulf of Mexico. Carbon content estimates were based on biovolume calculations derived from linear dimension measurements of individual cells and the approximate geometric body shape of each genus. Then, biomass assessments were performed for both groups in two gulf regions (Perdido and Coatzacoalcos) using these carbon content factors and cell abundances. After four seasonal cruises, 11,817 cells of dinoflagellates and 3,412 cells of diatoms were analyzed. Diverse body shapes and cell sizes were observed among 46 dinoflagellate genera and 37 diatom genera. Nano-cells of dinoflagellates (68% <20 μm) and micro-cells of diatoms (77% 20-200 μm, mostly 50-75 μm) were predominant. According to this cell-size structure, on average, diatoms contained 40% more carbon per cell than dinoflagellates. Contrasting carbon content estimates were observed within the genera of both microalgae. Large carbon averages (>10,000 pg C cell-1) were attributed to Gonyaulacal and some occasional genera of dinoflagellates (e.g., Pyrocystis and Noctiluca) and centric diatoms. In contrast, values up to 3 orders of magnitude lower were found for Peridinial and Gymnodinial dinoflagellates and pennate diatoms. Based on these carbon content estimates, which can be considered representative for most of this oceanic ecosystem, seasonal and regional differences were found in the biomass assessments conducted for these functional groups. Overall, dinoflagellates (mostly low-carbon Gymnodinales) had larger depth-integrated biomass than diatoms (mainly rich-carbon centric forms) within the euphotic zone. An exception to it was the late-summer cruise at the Coatzacoalcos region when a surface bloom of centric diatoms was observed in stations influenced by river runoff. This work contributes useful reference information for future ecological studies and models for understanding the biogeochemical functioning of this open-ocean ecosystem.

Adsorption of sulfonamides to marine diatoms and arthropods

Sulfonamides are frequently detected in the environment, where these compounds adsorb to soil particles and are retained in the environment. However, adsorption of sulfonamides to planktonic particles in the sea is not known. Here we demonstrate that sulfonamides adsorb to a diatom (Chaetoceros) and an arthropod (Artemia), albeit at low levels, under laboratory conditions. In both plankton, sulfamethazine (SMT) was more readily adsorbed than was sulfamethoxazole (SMX). The adsorption occurred quickly and the concentration on the plankton was stable for at least 24 h (Chaetoceros) or 5 h (Artemia). These data suggest that marine plankton may retain sulfonamides, although the adsorbed concentration per cell or individual is not high.

Diatom Bio-Silica and Cellulose Nanofibril for Bio-Triboelectric Nanogenerators and Self-Powered Breath Monitoring Masks

The application of biodegradable and biocompatible materials to triboelectric nanogenerators (TENGs) for harvesting energy from motions of the human body has been attracting significant research interest. Herein, we report diatom bio-silica as a biomaterial additive to enhance the output performance of cellulose nanofibril (CNF)-based TENGs. Diatom frustules (DFs), which are tribopositive bio-silica having hierarchically porous three-dimensional structures and high surface area, have hydrogen bonds with CNFs, resulting in enhanced electron-donating capability and a more roughened surface of the DF-CNF composite film. Hence, DFs were applied to form a tribopositive composite film with CNFs. The DF-CNF biocomposite film is mechanically strong, electron-rich, low-cost, and frictionally rough. The DF-CNF TENG showed an output voltage of 388 V and time-averaged power of 85.5 mW/m² in the contact-separation mode with an efficient contact area of 4.9 cm², and the generated power was sufficient for instantaneous illumination of 102 light-emitting diodes. In addition, a cytotoxicity study and biocompatibility tests on rabbit skin suggested that the DF-CNF composite was biologically safe. Moreover, a practical application of the DF-CNF TENG was examined with a self-powered smart mask for human breathing monitoring. This study not only suggests high output performance of biomaterial-based TENGs but also presents the diverse advantages of the DFs in human body-related applications such as self-powered health monitoring masks, skin-attachable power generators, and tactile feedback systems.

Visualization of elemental distributions and local analysis of element-specific chemical states of an Arachnoidiscus sp. frustule using soft X-ray spectromicroscopy

Using soft X-ray (SX) spectromicroscopy, we show maps of the spatial distribution of constituent elements and local analysis of the density of states (DOS) related to the element-specific chemical states of diatom frustules, which are composed of naturally grown nanostructured hydrogenated amorphous silica. We applied X-ray photoemission electron microscopy (X-PEEM) as well as microprobe X-ray fluorescence (μXRF) analysis to characterize the surfaces of diatom frustules by means of X-ray absorption spectroscopy (XAS) and X-ray emission spectroscopy (XES). We successfully demonstrated that SX spectromicroscopy is able to participate in potential observation tools as a new method to spectroscopically investigate diatom frustules.

Effects of Extraction Methods and Conditions on Bioactive Compounds Extracted from Phaeodactylum tricornutum

The effect of homogenization, ultrasound and microwave extraction methods and conditions on fucoxanthin content, total phenolic content and antioxidant activity of extracts obtained from Phaeodactylum tricornutum were investigated in this study. The solvent/biomass ratio was the most effective parameter on fucoxanthin content, total phenolic content and antioxidant activity. The maximum fucoxanthin content (5.60 ± 0.06 mg/g) and antioxidant activity (763.00 ± 15.88 EC50 ?g/mL extract) were obtained with the homogenization extraction method whose optimum conditions were 1.93% biomass/solvent ratio, ~5200 rpm homogenization rate and 14.2 min extraction time. Although the ultrasonic extraction method has reached the approximately same level of fucoxanthin content (5.24 ± 0.07 mg/g)), TPC (67.68 ± 1.58 mg gallic acid/L) and antioxidant activity (619.90 ± 17.16 EC50 ?g/mL extract) at an amplitude of 55.72%, a higher biomass/ solvent ratio (2.72%) and a longer extraction time (17.37 min) have been required. The lowest fucoxanthin content, total phenolic content and antioxidant activity were determined for the microwave extraction method.

Trimethylation of the R5 Silica-Precipitating Peptide Increases Silica Particle Size by Redirecting Orthosilicate Binding

The unmodified R5 peptide from silaffin in the diatom Cylindrotheca fusiformis rapidly precipitates silica particles from neutral aqueous solutions of orthosilicic acid. A range of post-translational modifications found in R5 contribute toward tailoring silica morphologies in a species-specific manner. We investigated the specific effect of R5 lysine side-chain trimethylation, which adds permanent positive charges, on silica particle formation. Our studies revealed that a doubly trimethylated R5K3,4me3 peptide has reduced maximum activity yet, surprisingly, generates larger silica particles. Molecular dynamics simulations of R5K3,4me3 binding by the precursor orthosilicate anion revealed that orthosilicate preferentially associates with unmodified lysine side-chain amines and the peptide N terminus. Thus, larger silica particles arise from reduced orthosilicate association with trimethylated lysine side chains and their redirection to the N terminus of the R5 peptide.

ERK1/2 Pathway Is Involved in the Enhancement of Fatty Acids from Phaeodactylum tricornutum Extract (PTE) on Hair Follicle Cell Proliferation

Extractions from Phaeodactylum tricornutum have been widely studied and evaluated to various biological effects. The aim of this study was to investigate the promotional effect of P. tricornutum extract (PTE) on the ERK1/2 signaling pathway involved in hair follicle cell proliferation. In order to illuminate the enhancement of PTE on hair growth by promoting proliferation of hair follicle cells, the activities of human hair follicle outer root sheath cell (HFORSC), human hair follicle germinal matrix cells (HFGMC), and hair epithelial melanocytes (HEM) were observed under PET treatment. Levels of keratins, PKCζ, ERK1/2, and p38 MAPK in hair follicle cells were determined by Western blotting to illustrate the mechanisms of PTE effects on hair growth. Analyzed by GC-MS, the main polyunsaturated fatty acids which were 9.43% of total fatty acids in PTE were linolenic acid, linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid. Melanin content and tyrosinase activity in HEM were measured. The results showed that PTE exhibited remarkable enhancement on cell proliferation. Melanin production was inhibited by PTE treatment, while keratin-14, keratin-15, and keratin-17 levels on hair follicle cells were elevated at different concentrations. The promotions of ERK1/2 and p38 MAPK levels indicated that the ERK1/2 signaling pathway is involved in the proliferation of hair follicle cells. These results are the evidence that PTE potentially deserves further study as a new natural candidate for hair care applications.

Improved Extraction Efficiency of Antioxidant Bioactive Compounds from Tetraselmis chuii and Phaedoactylum tricornutum Using Pulsed Electric Fields

Pulsed electric fields (PEF) is a promising technology that allows the selective extraction of high-added value compounds by electroporation. Thus, PEF provides numerous opportunities for the energy efficient isolation of valuable microalgal bioactive substances (i.e., pigments and polyphenols). The efficiency of PEF-assisted extraction combined with aqueous or dimethyl sulfoxide (DMSO) solvents in recovering pigments and polyphenols from microalgae Tetraselmis chuii (T. chuii) and Phaeodactylum tricornutum (P. tricornutum) was evaluated. Two PEF treatments were applied: (1 kV/cm/400 pulses, 3 kV/cm/45 pulses), with a specific energy input of 100 kJ/kg. The total antioxidant capacity (TAC) was positively influenced by the use of DMSO. The highest TAC in the T. chuii culture was achieved at a lower extraction time and electric field than for P. tricornutum. The use of DMSO only improved the polyphenols' extraction for P. tricornutum, whereas the PEF and extraction time were more important for T. chuii. Carotenoids and chlorophyll a were more efficiently extracted using DMSO, while chlorophyll b levels were higher following aqueous extraction for both microalgae. In P. tricornutum, the TAC and pigment extraction efficiency were in general higher at lower extraction times. It can be concluded that PEF may be a promising alternative for the enhancement of the selective extraction of antioxidant bioactive compounds from microalgae.

In-cell infrared difference spectroscopy of LOV photoreceptors reveals structural responses to light altered in living cells

Proteins are usually studied in well-defined buffer conditions, which differ substantially from those within a host cell. In some cases, the intracellular environment has an impact on the mechanism, which might be missed by in vitro experiments. IR difference spectroscopy previously has been applied to study the light-induced response of photoreceptors and photoenzymes in vitro Here, we established the in-cell IR difference (ICIRD) spectroscopy in the transmission and attenuated total reflection configuration to investigate the light-induced response of soluble proteins in living bacterial cells. ICIRD spectroscopy on the light, oxygen, or voltage (LOV) domains of the blue light receptors aureochrome and phototropin revealed a suppression of the response of specific secondary structure elements, indicating that the intracellular environment affects LOV photoreceptor mechanisms in general. Moreover, in-cell fluorescence spectroscopy disclosed that the intracellular environment slows down the recovery of the light-induced flavin adduct. Segment-resolved ICIRD spectroscopy on basic-region leucine zipper (bZIP)-LOV of aureochrome 1a from the diatom Phaeodactylum tricornutum indicated a signal progression from the LOV sensor to the bZIP effector independent of unfolding of the connecting A'α-helix, an observation that stood in contrast to in vitro results. This deviation was recapitulated in vitro by emulating the intracellular environment through the addition of the crowding agent BSA, but not by sucrose polymers. We conclude that ICIRD spectroscopy is a noninvasive, label-free approach for assessing conformational changes in receptors in living cells at ambient conditions. As demonstrated, these near-native responses may deviate from the mechanisms established under in vitro conditions.

Ambient temperature and algal prey type affect essential fatty acid incorporation and trophic upgrading in a herbivorous marine copepod

The essential fatty acids (EFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are critical nutrients for all organisms, and the temperature sensitivity of their trophic transfer in marine systems is of concern because of rising ocean temperatures. Laboratory-reared copepodites of the marine calanoid Calanus finmarchicus were used to test the effects of temperature (at 6°C, 12°C and increasing temperature stress) and prey type (the dinoflagellate Heterocapsa triquetra and the diatom Thalassiosira weissflogii) on the extent and efficiency of dietary EPA and DHA incorporation from phytoplankton to copepods in a set of feeding experiments using 13C labelling. Temperature was a significant determinant of C. finmarchicus copepodites' EFA incorporation and gross growth efficiency, defined as the fraction of ingested EFA retained in copepod tissue. Ingestion and incorporation of both EFA were higher at warmer temperature, except in the case of DHA in copepods feeding on diatoms. DHA-associated growth efficiency was higher at the higher temperature for copepodites consuming the dinoflagellate, but temperature-related variation in algal EFA content was also a predictive factor. Moreover, our results strongly suggest that copepodites are capable of synthesizing EPA when consuming an EPA-depleted diet. Our study implies that the copepod link of marine food webs is resilient in terms of EFA transfer when confronted with alterations of ambient temperature and prey type availability. Measurements presented here are critical for estimating how EFA transfer dynamics respond to intra- and interannual environmental variability. This article is part of the theme issue 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Diatom-Derived Polyunsaturated Aldehydes Activate Similar Cell Death Genes in Two Different Systems: Sea Urchin Embryos and Human Cells

Programmed cell death, such as apoptosis and autophagy, are key processes that are activated early on during development, leading to remodelling in embryos and homeostasis in adult organisms. Genomic conservation of death factors has been largely investigated in the animal and plant kingdoms. In this study, we analysed, for the first time, the expression profile of 11 genes involved in apoptosis (extrinsic and intrinsic pathways) and autophagy in sea urchin Paracentrotus lividus embryos exposed to antiproliferative polyunsaturated aldehydes (PUAs), and we compared these results with those obtained on the human cell line A549 treated with the same molecules. We found that sea urchins and human cells activated, at the gene level, a similar cell death response to these compounds. Despite the evolutionary distance between sea urchins and humans, we observed that the activation of apoptotic and autophagic genes in response to cytotoxic compounds is a conserved process. These results give first insight on death mechanisms of P. lividus death mechanisms, also providing additional information for the use of this marine organism as a useful in vitro model for the study of cell death signalling pathways activated in response to chemical compounds.

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.

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.