AFM imaging of extracellular polymer release by marine diatom Cylindrotheca closterium (Ehrenberg) Reiman & J.C. Lewin

Neuroprotective Effects of Dehydroepiandrosterone Sulphate Against Aβ Toxicity and Accumulation in Cellular and Animal Model of Alzheimer's Disease

Background/Objectives: Beneficial effects of neurosteroid dehydroepiandrosterone sulphate (DHEAS) on cognition, emotions and behavior have been previously reported, suggesting its potential in the prevention and treatment of various neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease (AD). This study aimed to investigate the potential neuroprotective actions of DHEAS against Aβ toxicity in both cellular and animal models of AD. Methods: After optimizing the AD model in vitro, we investigated the DHEAS effects on the viability and death of primary mouse neurons exposed to toxic Aβ42 oligomers for 24 h. In order to extend our research to an in vivo study, we further tested the acute effects of intraperitoneal DHEAS administration on the Aβ plaque density in different brain regions of 3xTg-AD mice, an animal model of AD. Results: In cell culture, DHEAS hampered the decrease in the neuronal viability caused by toxic Aβ oligomers, primarily by influencing mitochondrial function and apoptosis. DHEAS also counteracted the increase in the mRNA expression of selected genes (PI3K, Akt, Bcl2, Bax), induced in neuronal culture by treatment with Aβ42 oligomers. Obtained data suggested the involvement of mitochondria, caspases 3 and 7, as well as the PI3K/Akt and Bcl2 signaling network in the antiapoptotic properties of DHEAS in neurons. Forty-eight hours after DHEAS treatment, a significantly lower number of Aβ plaques was observed in the motor cortex but not in other brain areas of 3xTg-AD mice. Conclusions: Results indicated potential neuroprotective effects of DHEAS against Aβ toxicity and accumulation, suggesting that DHEAS supplementation should be further studied as a novel option for AD prevention and/or treatment.

Investigation of the role of cell hydrophobicity and EPS production in the aggregation of the marine diatom Cylindrotheca closterium under hypo-saline conditions

Aggregation of diatoms is of global importance to understand settling of particulate organic carbon in aquatic systems. In this study, we investigate the aggregation of the marine diatom Cylindrotheca closterium during the exponential growth phase under hypo-saline conditions. The results of the flocculation/flotation experiments show that the aggregation of the diatom depends on the salinity. In favorable growth conditions for marine diatoms (salinity of 35), the highest aggregation is achieved. To explain these observations, we used a surface approach combining atomic force microscopy (AFM) and electrochemical methods to characterize both the cell surface properties and the structure of the extracellular polymeric substances (EPS) cell produce, and to quantify the amount of surface-active organic matter released. At a salinity of 35, the results showed that diatoms are soft, hydrophobic and release only small amounts of EPS organized into individual short fibrils. In contrast, diatoms adapt to a salinity of 5 by becoming much stiffer and more hydrophilic, producing larger amounts of EPS that structurally form an EPS network. Both adaptation responses of diatoms, the hydrophobic properties of diatoms and the release of EPS, appear to play an important role in diatom aggregation and explain the behavior observed at different salinities. This biophysical study provides important evidence allowing to get a deep insight into diatom interactions at the nanoscale, which may contribute to a better understanding of large-scale aggregation phenomena in aquatic systems.

Reconstructed membrane vesicles from the microalga Dunaliella as a potential drug delivery system

The aim of this biophysical study is to characterize reconstructed membrane vesicles obtained from microalgae in terms of their morphology, properties, composition, and ability to transport a model drug. The reconstructed vesicles were either emptied or non-emptied and exhibited a non-uniform distribution of spherical surface structures that could be associated with surface coat proteins, while in between there were pore-like structures of up to 10 nm that could contribute to permeability. The reconstructed vesicles were very soft and hydrophilic, which could be attributed to their composition. The vesicles were rich in proteins and were mostly derived from the cytoplasm and chloroplasts. We demonstrated that all lipid classes of D. tertiolecta are involved in the formation of the reconstructed membrane vesicles, where they play fundamental role to maintain the vesicle structure. The vesicles appeared to be permeable to calcein, impermeable to FITC-ovalbumin, and semipermeable to FITC-concanavalin A, which may be due to a specific surface interaction with glucose/mannose units that could serve as a basis for the development of drug carriers. Finally, the reconstructed membrane vesicles could pave a new way as sustainable and environmentally friendly marine bioinspired carriers and serve for studies on microtransport of materials and membrane-related processes contributing to advances in life sciences and biotechnology.

Bacterial surface interactions with organic colloidal particles: Nanoscale hotspots of organic matter in the ocean

Colloidal particles constitute a substantial fraction of organic matter in the global ocean and an abundant component of the organic matter interacting with bacterial surfaces. Using E. coli ribosomes as model colloidal particles, we applied high-resolution atomic force microscopy to probe bacterial surface interactions with organic colloids to investigate particle attachment and relevant surface features. We observed the formation of ribosome films associating with marine bacteria isolates and natural seawater assemblages, and that bacteria readily utilized the added ribosomes as growth substrate. In exposure experiments ribosomes directly attached onto bacterial surfaces as 40–200 nm clusters and patches of individual particles. We found that certain bacterial cells expressed surface corrugations that range from 50–100 nm in size, and 20 nm deep. Furthermore, our AFM studies revealed surface pits in select bacteria that range between 50–300 nm in width, and 10–50 nm in depth. Our findings suggest novel adaptive strategies of pelagic marine bacteria for colloid capture and utilization as nutrients, as well as storage as nanoscale hotspots of DOM.

Nanoplastic-Induced Nanostructural, Nanomechanical, and Antioxidant Response of Marine Diatom Cylindrotheca closterium

The aim of this study was to examine the effect of positively charged (amine-modified) and negatively charged (carboxyl-modified) polystyrene nanoplastics (PS NPs) on the nanostructural, nanomechanical, and antioxidant responses of the marine diatom Cylindrotheca closterium. The results showed that both types of PS NPs, regardless of surface charge, significantly inhibited the growth of C. closterium during short-term exposure (3 and 4 days). However, longer exposure (14 days) to both PS NPs types did not significantly inhibit growth, which might be related to the detoxifying effect of the microalgal extracellular polymers (EPS) and the higher cell abundance per PS NPs concentration. The exposure of C. closterium to both types of PS NPs at concentrations above the corresponding concentrations that resulted in a 50% reduction of growth (EC50) demonstrated phytotoxic effects, mainly due to the excessive production of reactive oxygen species, resulting in increased oxidative damage to lipids and changes to antioxidant enzyme activities. Diatoms exposed to nanoplastics also showed a significant decrease in cell wall rigidity, which could make the cells more vulnerable. Atomic force microscopy images showed that positively charged PS NPs were mainly adsorbed on the cell surface, while both types of PS NPs were incorporated into the EPS that serves to protect the cells. Since microalgal EPS are an important food source for phytoplankton grazers and higher trophic levels, the incorporation of NPs into the EPS and interactions with the cell walls themselves may pose a major threat to marine microalgae and higher trophic levels and, consequently, to the health and stability of the marine ecosystem.

Microrheology reveals microscale viscosity gradients in planktonic systems

At the microscopic scales at which the life of marine microbes unfolds, the physics is dominated by viscosity. Increasing viscosity slows down both the passive transport of solutes and particles and the swimming of motile microorganisms, and thus directly or indirectly affects all aspects of microbial life. Viscosity depends not only on the physical properties of water, but it also varies as a consequence of biological activity, allowing microorganisms some control over their physical landscape. Our use of microrheology allows us to explore how viscosity is structured around phytoplankton cells and marine aggregates and unveils a level of spatial heterogeneity that has implications for the functioning of the microbial food web and hence of marine biogeochemical cycles.

Microbial activity in planktonic systems creates a dynamic and heterogeneous microscale seascape that harbors a diverse community of microorganisms and ecological interactions of global significance. In recent decades great effort has been put into understanding this complex system, particularly focusing on the role of chemical patchiness, while overlooking a physical parameter that governs microbial life and is affected by biological activity: viscosity. Here we reveal spatial heterogeneity of viscosity in planktonic systems by using microrheological techniques that allow measurement of viscosity at length scales relevant to microorganisms. We show the viscous nature and the spatial extent of the phycosphere, the region surrounding phytoplankton. In ∼45% of the phytoplankton cells analyzed we detected increases in viscosity that extended up to 30 µm away from the cell with up to 40 times the viscosity of seawater. We also show how these gradients of viscosity can be amplified around a lysing phytoplankton cell as its viscous contents leak away. Finally, we report conservative estimates of viscosity inside marine aggregates, hotspots of microbial activity, more than an order of magnitude higher than in seawater. Since the diffusivities of dissolved molecules, particles, and microorganisms are inversely related to viscosity, microheterogeneity in viscosity alters the microscale distribution of microorganisms and their resources, with pervasive implications for the functioning of the planktonic ecosystem. Increasing viscosities impacts ecological interactions and processes, such as nutrient uptake, chemotaxis, and particle encounter, that occur at the microscale but influence carbon and nutrient cycles at a global scale.

The Impact of Antarctic Ice Microalgae Polysaccharides on D-Galactose-Induced Oxidative Damage in Mice

Antarctic ice microalgae (Chlamydomonas sp.) are a polysaccharide-rich natural marine resource. In this study, we evaluated the impact of Antarctic ice microalgae polysaccharides (AIMP) on D-galactose-induced oxidation in mice. We conducted biological and biochemical tests on tissue and serum samples from mice treated with AIMP. We found that AIMP administration was associated with improved thymus, brain, heart, liver, spleen, and kidney index values. We also found that AIMP treatment inhibited the reduced aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, superoxide dismutase, glutathione peroxidase, and glutathione levels as well as the increased serum, splenic, and hepatic nitric oxide and malondialdehyde levels arising from oxidation in these animals. Pathological examination revealed that AIMP also inhibited D-galactose-induced oxidative damage to the spleen, liver, and skin of these animals. AIMP was additionally found to promote the upregulation of neuronal nitric oxide synthase, endothelial nitric oxide synthase, cuprozinc-superoxide dismutase, manganese superoxide dismutase, catalase, heme oxygenase-1, nuclear factor erythroid 2-related factor 2, γ-glutamylcysteine synthetase, and NAD(P)H dehydrogenase [quinone] 1 as well as the downregulation of inducible nitric oxide synthase in these animals. High-performance liquid chromatography analysis revealed AIMP to be composed of five monosaccharides (mannitol, ribose, anhydrous glucose, xylose, and fucose). Together, these results suggest that AIMP can effectively inhibit oxidative damage more readily than vitamin C in mice with D-galactose-induced oxidative damage, which underscores the value of developing AIMP derivatives for food purposes.

Thermal Niche Differentiation in the Benthic Diatom Cylindrotheca closterium (Bacillariophyceae) Complex

Coastal waters are expected to undergo severe warming in the coming decades. Very little is known about how diatoms, the dominant primary producers in these habitats, will cope with these changes. We investigated the thermal niche of Cylindrotheca closterium, a widespread benthic marine diatom, using 24 strains collected over a wide latitudinal gradient. A multi-marker phylogeny in combination with a species delimitation approach shows that C. closterium represents a (pseudo)cryptic species complex, and this is reflected in distinct growth response patterns in terms of optimum growth temperature, maximum growth rate, and thermal niche width. Strains from the same clade displayed a similar thermal response, suggesting niche conservation between closely related strains. Due to their lower maximum growth rate and smaller thermal niche width, we expect the polar species to be particularly sensitive to warming, and, in the absence of adaptation, to be replaced with species from lower latitudes.

Can diatom girdle band pores act as a hydrodynamic viral defense mechanism?

Diatoms are microalgae encased in highly structured and regular frustules of porous silica. A long-standing biological question has been the function of these frustules, with hypotheses ranging from them acting as photonic light absorbers to being particle filters. While it has been observed that the girdle band pores of the frustule of Coscinodiscus sp. resemble those of a hydrodynamic drift ratchet, we show using scaling arguments and numerical simulations that they cannot act as effective drift ratchets. Instead, we present evidence that frustules are semi-active filters. We propose that frustule pores simultaneously repel viruses while promoting uptake of ionic nutrients via a recirculating, electroosmotic dead-end pore flow, a new mechanism of "hydrodynamic immunity".

Windows into Microbial Seascapes: Advances in Nanoscale Imaging and Application to Marine Sciences

Geochemical cycles of all nonconservative elements are mediated by microorganisms over nanometer spatial scales. The pelagic seascape is known to possess microstructure imposed by heterogeneous distributions of particles, polymeric gels, biologically important chemicals, and microbes. While indispensable, most traditional oceanographic observational approaches overlook this heterogeneity and ignore subtleties, such as activity hot spots, symbioses, niche partitioning, and intrapopulation phenotypic variations, that can provide a deeper mechanistic understanding of planktonic ecosystem function. As part of the movement toward cultivation-independent tools in microbial oceanography, techniques to examine the ecophysiology of individual populations and their role in chemical transformations at spatial scales relevant to microorganisms have been developed. This review presents technologies that enable geochemical and microbiological interrogations at spatial scales ranging from 0.02 to a few hundred micrometers, particularly focusing on atomic force microscopy, nanoscale secondary ion mass spectrometry, and confocal Raman microspectroscopy and introducing promising approaches for future applications in marine sciences.

Live diatoms facing Ag nanoparticles: surface enhanced Raman scattering of bulk cylindrotheca closterium pennate diatoms and of the single cells

Live diatoms exposed to AgNPs revealed SERS mechanism dependent on the nanoparticles type while the SERS output allowed detection of extracellular substances.

Self-assembly of polysaccharides gives rise to distinct mechanical signatures in marine gels

Marine-gel biopolymers were recently visualized at the molecular level using atomic force microscopy (AFM) to reveal fine fibril-forming networks with low to high degrees of cross-linking. In this work, we use force spectroscopy to quantify the intra- and intermolecular forces within the marine-gel network. Combining force measurements, AFM imaging, and the known chemical composition of marine gels allows us to identify the microscopic origins of distinct mechanical responses. At the single-fibril level, we uncover force-extension curves that resemble those of individual polysaccharide fibrils. They exhibit entropic elasticity followed by extensions associated with chair-to-boat transitions specific to the type of polysaccharide at high forces. Surprisingly, a low degree of cross-linking leads to sawtooth patterns that we attribute to the unraveling of polysaccharide entanglements. At a high degree of cross-linking, we observe force plateaus that arise from unzipping, as well as unwinding, of helical bundles. Finally, the complex 3D network structure gives rise to force staircases of increasing height that correspond to the hierarchical peeling of fibrils away from the junction zones. In addition, we show that these diverse mechanical responses also arise in reconstituted polysaccharide gels, which highlights their dominant role in the mechanical architecture of marine gels.

Marine polysaccharides from algae with potential biomedical applications

There is a current tendency towards bioactive natural products with applications in various industries, such as pharmaceutical, biomedical, cosmetics and food. This has put some emphasis in research on marine organisms, including macroalgae and microalgae, among others. Polysaccharides with marine origin constitute one type of these biochemical compounds that have already proved to have several important properties, such as anticoagulant and/or antithrombotic, immunomodulatory ability, antitumor and cancer preventive, antilipidaemic and hypoglycaemic, antibiotics and anti-inflammatory and antioxidant, making them promising bioactive products and biomaterials with a wide range of applications. Their properties are mainly due to their structure and physicochemical characteristics, which depend on the organism they are produced by. In the biomedical field, the polysaccharides from algae can be used in controlled drug delivery, wound management, and regenerative medicine. This review will focus on the biomedical applications of marine polysaccharides from algae.

Algal and microbial exopolysaccharides: new insights as biosurfactants and bioemulsifiers

Currently, efforts are being made to utilize more natural biological systems as alternatives as a way to replace fossil forms of carbon. There is a growing concern at global level to have nontoxic, nonhazardous surface-active agents; contrary to synthetic surfactants, their biological counterparts or biosurfactants play a primary function, facilitating microbial presence in environments dominated by hydrophilic-hydrophobic interfaces. Algal and microbial biosurfactants/bioemulsifiers from marine and deep-sea environments are attracting major interest due to their structural and functional diversity as molecules actives of surface and an alternative biomass to replace fossil forms of carbon. Algal and microbial surfactants are lipid in nature and classified as glycolipids, phospholipids, lipopeptides, natural lipids, fatty acids, and lipopolysaccharides. These metabolic bioactive products are applicable in a number of industries and processes, viz., food processing, pharmacology, and bioremediation of oil-polluted environments. This chapter presents an update of the progress and potentialities of the principal producers of exopolysaccharide (EPS)-type biosurfactants and bioemulsifiers, viz., macro- and microalgae (cyanobacteria and diatoms) and bacteria from marine and extreme environments. Particular interest is centered into new sources and applications, viz., marine and deep-sea environments and promissory uses of these EPSs as biosurfactants/emulsifiers and other polymeric roles. The enormous benefits of these molecules encourage their discovery, exploitation, and development of new microbial EPSs that could possess novel industrial importance and corresponding innovations.

Marine polysaccharide networks and diatoms at the nanometric scale

Despite many advances in research on photosynthetic carbon fixation in marine diatoms, the biophysical and biochemical mechanisms of extracellular polysaccharide production remain significant challenges to be resolved at the molecular scale in order to proceed toward an understanding of their functions at the cellular level, as well as their interactions and fate in the ocean. This review covers studies of diatom extracellular polysaccharides using atomic force microscopy (AFM) imaging and the quantification of physical forces. Following a brief summary of the basic principle of the AFM experiment and the first AFM studies of diatom extracellular polymeric substance (EPS), we focus on the detection of supramolecular structures in polysaccharide systems produced by marine diatoms. Extracellular polysaccharide fibrils, attached to the diatom cell wall or released into the surrounding seawater, form distinct supramolecular assemblies best described as gel networks. AFM makes characterization of the diatom polysaccharide networks at the micro and nanometric scales and a clear distinction between the self-assembly and self-organization of these complex systems in marine environments possible.

Underwater locomotion strategy by a benthic pennate diatom Navicula sp

The mechanism of diatom locomotion has been widely researched but still remains a hypothesis. There are several questionable points on the prevailing model proposed by Edgar, and some of the observed phenomena cannot be completely explained by this model. In this paper, we undertook detailed investigations of cell structures, locomotion, secreted mucilage, and bending deformation for a benthic pennate diatom Navicula species. According to these broad evidences, an updated locomotion model is proposed. For Navicula sp., locomotion is realized via two or more pseudopods or stalks protruded out of the frustules. The adhesion can be produced due to the pull-off of one pseudopod or stalk from the substratum through extracellular polymeric substances. And the positive pressure is generated to balance the adhesion because of the push-down of another pseudopod or stalk onto the substratum. Because of the positive pressure, friction is generated, acting as a driving force of locomotion, and the other pseudopod or stalk can detach from the substratum, resulting in the locomotion. Furthermore, this model is validated by the force evaluation and can better explain observed phenomena. This updated model would provide a novel aspect on underwater locomotion strategy, hence can be useful in terms of artificial underwater locomotion devices.

Bioactivity and applications of sulphated polysaccharides from marine microalgae

Marine microalgae have been used for a long time as food for humans, such as Arthrospira (formerly, Spirulina), and for animals in aquaculture. The biomass of these microalgae and the compounds they produce have been shown to possess several biological applications with numerous health benefits. The present review puts up-to-date the research on the biological activities and applications of polysaccharides, active biocompounds synthesized by marine unicellular algae, which are, most of the times, released into the surrounding medium (exo- or extracellular polysaccharides, EPS). It goes through the most studied activities of sulphated polysaccharides (sPS) or their derivatives, but also highlights lesser known applications as hypolipidaemic or hypoglycaemic, or as biolubricant agents and drag-reducers. Therefore, the great potentials of sPS from marine microalgae to be used as nutraceuticals, therapeutic agents, cosmetics, or in other areas, such as engineering, are approached in this review.

A novel type of colony formation in marine planktonic diatoms revealed by atomic force microscopy

Diatoms have evolved a variety of colonial life forms in which cells are connected by organic threads, mucilage pads or silicate structures. In this study, we provide the first description of a novel strategy of colony formation among marine planktonic diatoms. Bacteriastrum jadranum forms loose but regular chains with distinct heterovalvate terminal cells. The colonial cells and their siliceous projections, the setae, are not in direct contact; instead, they are enclosed within the optically transparent organic matrix. This cell jacket structure was detected by staining procedure with Alcian Blue, which showed that the polysaccharides are predominant matrix constituents and revealed that the jacket reaches the span of the setae. The scanning electron microscopy (SEM) observations showed distinguishable fibrillar network firmly associated with cells. Using atomic force microscopy (AFM), we were able to visualise and characterise the cell jacket structure at molecular resolution. At nanoscale resolution, the cell jacket appears as a cross-linked fibrillar network organised into a recognisable structure. The circular patches of self-repeating pattern (hexagonal pores with openings of 8-100 nm) are connected through thicker surrounding fibrils and reinforced by branching fibrils. The pore-forming fibrils within the patches are only 0.6-1.6 nm high, the surrounding fibrils connecting patches are 2.0-2.8 nm high, and the branching fibrils are considerably wider but not higher than 4.0 nm. The discovered polysaccharide fibrillar network is highly organised and delicately structured with a monomolecular fibril height of 0.6 nm. We conclude that the Bacteriastrum polysaccharide jacket represents an essential part of the cell, as the conjunction of the polymer network with the frustule appears to be extremely tight and such specific and unique patterns have never been found in self-assembled polysaccharide gel networks, which are usually encountered in the marine environment.

Toxin-producing Ostreopsis cf. ovata are likely to bloom undetected along coastal areas

Mass appearances of the toxic dinoflagellate genus Ostreopsis are known to cause dangerous respiratory symptoms in humans exposed to aerosols. The outbreaks can appear in shallow marine waters of temperate regions around the globe. We followed a massive bloom event on a public beach on the northern Adriatic coast near Rovinj, Croatia. We identified the responsible species and the produced toxins as well as the dynamics of the event with respect to environmental conditions. Ostreopsis cf. ovata appeared in masses from September through October 2010 on a public beach near Rovinj, Croatia but stayed undetected by public health organizations. Respiratory symptoms were observed whenever humans were exposed to substrate samples containing large numbers of Ostreopsis cells. During the mass abundance of O. cf. ovata also exposure to the aerosols on the beach evoked respiratory symptoms in humans. Our measurements showed high cell abundances and high toxin contents with a stable relative contribution of putative Palytoxin and Ovatoxins a-e. Artificial beach structures proved to dramatically reduce settling of the observed Ostreopsis biofilm. Blooms like those reported herein have a high potential to happen undetected with a high potential of affecting the health of coastal human populations. Increased monitoring efforts are therefore required to understand the ecology and toxicology of those bloom events and reduce their negative impact on coastal populations.

QUANTITATIVE NANOMECHANICAL MAPPING OF MARINE DIATOM IN SEAWATER USING PEAK FORCE TAPPING ATOMIC FORCE MICROSCOPY(1)

It is generally accepted that a diatom cell wall is characterized by a siliceous skeleton covered by an organic envelope essentially composed of polysaccharides and proteins. Understanding of how the organic component is associated with the silica structure provides an important insight into the biomineralization process and patterning on the cellular level. Using a novel atomic force microscopy (AFM) imaging technique (Peak Force Tapping), we characterized nanomechanical properties (elasticity and deformation) of a weakly silicified marine diatom Cylindrotheca closterium (Ehrenb.) Reimann et J. C. Lewin (strain CCNA1). The nanomechanical properties were measured over the entire cell surface in seawater at a resolution that was not achieved previously. The fibulae were the stiffest (200 MPa) and the least deformable (only 1 nm). Girdle band region appeared as a series of parallel stripes characterized by two sets of values of Young's modulus and deformation: one for silica stripes (43.7 Mpa, 3.7 nm) and the other between the stripes (21.3 MPa, 13.4 nm). The valve region was complex with average values of Young's modulus (29.8 MPa) and deformation (10.2 nm) with high standard deviations. After acid treatment, we identified 15 nm sized silica spheres in the valve region connecting raphe with the girdle bands. The silica spheres were neither fused together nor forming a nanopattern. A cell wall model is proposed with individual silica nanoparticles incorporated in an organic matrix. Such organization of girdle band and valve regions enables the high flexibility needed for movement and adaptation to different environments while maintaining the integrity of the cell.

Polymer networks produced by marine diatoms in the northern Adriatic sea

Using high resolution molecular technique of atomic force microscopy, we address the extracellular polymer production of Adriatic diatom Cylindrotheca closterium analyzed at the single cell level and the supramolecular organization of gel phase isolated from the Northern Adriatic macroaggregates. Our results revealed that extracellular polysaccharides freshly produced by marine diatoms can self-assemble directly to form gel network characteristics of the macroscopic gel phase in the natural aquatorium. Based on the experiments performed with isolated polysaccharide fractions of C. closterium and of macroaggregates gel phase, we demonstrated that the polysaccharide self-assembly into gel network can proceed independent of any bacterial mediation or interaction with inorganic particles.