The protective effect of Nostoc commune Vauch. polysaccharide on alcohol-induced acute alcoholic liver disease and gut microbiota disturbance in mice.

BACKGROUND: In recent years, the incidence of alcoholic liver disease (ALD) has gradually increased, the development of ALD is attached great attentions. Nostoc commune Vauch. polysaccharide (NCVP) is beneficial to maintain the gut health, but the protective effect of NCVP on the liver has not been reported yet. PURPOSE: To study the protective effect and the underlying mechanisms of NCVP on ALD, a mouse model of acute ALD was established. STUDY DESIGN AND METHODS: We built an acute ALD mouse model and explored the protective effect of NCVP through the detection of cytokines, histological examination, determination of short chain fatty acids, and 16S rRNA analysis of gut microbiota. RESULTS: NCVP had hepatoprotective effects on acute alcohol-induced mice by improving antioxidant capacity, reducing oxidative stress and the serum cytokine levels (IL-1ß, IL-6, and TNF-α). Simultaneously, histopathological changes in liver indicated that NCVP could inhibit local hepatocyte necrosis, cytoplasmic vacuolation and inflammatory cell infiltration induced by alcohol. NCVP also increased the level of total short-chain fatty acids of acute ALD mice. In addition, NCVP could significantly decrease the Firmicutes/Bacteroidetes ratio and the abundance of Patescibacteria, Helicobacter, and Actinomycetes and increase the abundance of Lachospiraceae, Prevotellaceae-UCG-003, Lactobacillaceae, and Desulfovibrio. CONCLUSION: Our study proved that NCVP had in vivo hepatoprotective effect on acute ALD mice and provided scientific evidences that NCVP might be a promising drug candidate for the prevention and treatment of ALD.

Efficient separation of phycocyanin of Nostoc commune by multistep diafiltration using ultra-filtration membrane modules.

Diafiltration (DF) is a separation method used to separate and concentrate macromolecules, such as polysaccharides and proteins. To obtain high-purity target molecules by DF, appropriate conditions should be used. In this study, a mathematical model was developed to suggest appropriate ultra-filtration (UF) membrane modules for the separation of phycocyanin (PC) by multistep DF. PC is a protein produced by microalgae. The contribution of each UF membrane module to PC productivity and purity at each stage of the multistep DF process was quantified by the proposed model. The parameters required as model inputs (k, Fα1, and Fα2) were experimentally determined by permeating PC-containing solution through UF membrane modules (150, 30, and 10 kDa cutoffs). The resulting analytical solutions and those predicted by the model were in close agreement. The PC purity increased from 0.20 to 0.30 when a 10 kDa UF membrane module was used in two-step DF. An orthogonal table was used to determine the combination of UF membrane modules needed to achieve higher purity of PC. The model predicted that the 30 kDa UF membrane module would have the highest contribution to PC productivity and purity at any position in a three-step DF. The developed model can help identify appropriate conditions for separating macromolecules by DF.

Efficient Lead Pb(II) Removal with Chemically Modified Nostoc commune Biomass.

A new biosorbent based on Nostoc commune (NC) cyanobacteria, chemically modified with NaOH (NCM), has been prepared, characterized and tested as an effective biomass to remove Pb(II) in aqueous media. The adsorption capacity of NCM was determined to be qe = 384.6 mg g−1. It is higher than several other biosorbents reported in the literature. Structural and morphological characterization were performed by FTIR, SEM/EDX and point zero of charge pH (pHPZC) measurements. NCM biosorbent showed more porous surfaces than those NC with heterogeneous plates including functional adsorption groups such as OH, C = O, COO−, COH or NH. Optimal Pb(II) adsorption occurred at pH 4.5 and 5.5 with a biomass dose of 0.5 g L−1. The experimental data of the adsorption process were well fitted with the Freundlich-isotherm model and pseudo-2nd order kinetics, which indicated that Pb(II) adsorption was a chemisorption process on heterogeneous surfaces of NCM. According to the thermodynamic parameters, this process was exothermic (∆H0 < 0), feasible and spontaneous (∆G0 < 0). NCM can be regenerated and efficiently reused up to 4 times (%D > 92%). NCM was also tested to remove Pb (%R~98%) and Ca (%R~64%) from real wastewater.

Recombinant water stress protein 1 (Re-WSP1) suppresses colon cancer cell growth through the miR-539/ß-catenin signaling pathway.

BACKGROUND: Nostoc commune Vauch. is a nitrogen-fixing blue-green algae that expresses a large number of active molecules with medicinal properties. Our previous study found that a water stress protein (WSP1) from N. commune and its recombinant counterpart (Re-WSP1) exhibited significant anti-colon cancer activity both in vitro and in vivo. This study is to investigate the effects of Re-WSP1 on proliferation of colon cancer cells and to elucidate the relevant mechanisms. METHODS: Real-time quantitative PCR was used to detect the expression of miR-539 in colon cancer HT-29 and DLD1 cells. Colon cancer cells were transfected with miR-539 mimics and negative controls, and cell proliferation were detected by CCK8 and clonogenic assays. The target gene of miR-539 was predicted, and the dual luciferase reporter gene experiment was used to verify the target gene. After colon cancer cells were transfected with miR-539 mimics or inhibitors, the expression of target gene ß-catenin was detected by Western blot. miR-539 inhibitor confirmed cell proliferation. RESULTS: Re-WSP1 inhibited colon cancer cell growth in a dose-dependent manner. Re-WSP1 inhibited the expression of ß-catenin, which was partly reversed by LiCl treatment. Quantitative PCR analysis showed that the expression of miR-539 was significantly upregulated after Re-WSP1 treatment. Moreover, miR-539 negatively regulated the expression of ß-catenin by directly binding to the 3'UTR of ß-catenin mRNA. The cell growth inhibition and the decrease in ß-catenin expression induced by Re-WSP1 were significantly reversed by miR-539 inhibitor. CONCLUSION: Re-WSP1 suppresses colon cancer cell growth via the miR-539/ß-catenin axis.

Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments.

BACKGROUND: The cyanobacterial genus Nostoc includes several species forming centimetre-large gelatinous colonies in nutrient-poor freshwaters and harsh semi-terrestrial environments with extended drought or freezing. These Nostoc species have filaments with normal photosynthetic cells and N2-fixing heterocysts embedded in an extensive gelatinous matrix of polysaccharides and many other organic substances providing biological and environmental protection. Large colony size imposes constraints on the use of external resources and the gelatinous matrix represents extra costs and reduced growth rates. SCOPE: The objective of this review is to evaluate the mechanisms behind the low rates of growth and mortality, protection against environmental hazards and the persistence and longevity of gelatinous Nostoc colonies, and their ability to economize with highly limiting resources. CONCLUSIONS: Simple models predict the decline in uptake of dissolved inorganic carbon (DIC) and a decline in the growth rate of spherical freshwater colonies of N. pruniforme and N. zetterstedtii and sheet-like colonies of N. commune in response to a thicker diffusion boundary layer, lower external DIC concentration and higher organic carbon mass per surface area (CMA) of the colony. Measured growth rates of N. commune and N. pruniforme at high DIC availability comply with general empirical predictions of maximum growth rate (i.e. doubling time 10-14 d) as functions of CMA for marine macroalgae and as functions of tissue thickness for aquatic and terrestrial plants, while extremely low growth rates of N. zetterstedtii (i.e. doubling time 2-3 years) are 10-fold lower than model predictions, either because of very low ambient DIC and/or an extremely costly colony matrix. DIC uptake is limited by diffusion at low concentrations for all species, although they exhibit efficient HCO3(-) uptake, accumulation of respiratory DIC within the colonies and very low CO2 compensation points. Long light paths and light attenuation by structural substances in large Nostoc colonies cause lower quantum efficiency and assimilation number and higher light compensation points than in unicells and other aquatic macrophytes. Extremely low growth and mortality rates of N. zetterstedtii reflect stress-selected adaptation to nutrient- and DIC-poor temperate lakes, while N. pruniforme exhibits a mixed ruderal- and stress-selected strategy with slow growth and year-long survival prevailing in sub-Arctic lakes and faster growth and shorter longevity in temperate lakes. Nostoc commune and its close relative N. flagelliforme have a mixed stress-disturbance strategy not found among higher plants, with stress selection to limiting water and nutrients and disturbance selection in quiescent dry or frozen stages. Despite profound ecological differences between species, active growth of temperate specimens is mostly restricted to the same temperature range (0-35 °C; maximum at 25 °C). Future studies should aim to unravel the processes behind the extreme persistence and low metabolism of Nostoc species under ambient resource supply on sediment and soil surfaces.

Effects of Nostoc commune extract on the cerebral oxidative and neuroinflammatory status in a mice model of schizophrenia.

Cyanobacterium Nostoc commune has long been used to alleviate various diseases. This research examines the effects of Nostoc commune extract (NCE) against behavioral disorders, cerebral oxidative stress, and inflammatory damage in the ketamine-induced schizophrenia model. Oral NCE administration (70 and 150 mg/kg/d) is performed after intraperitoneal ketamine injection (20 mg/kg) for 14 consecutive days. The forced swimming and open field tests are used to assess schizophrenia-like behaviors. After the behavioral test, dopamine (DA) level, oxidative stress markers, as well as the interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) expression are measured in the cerebral cortex. The results show that NCE treatment ameliorates KET-induced anxiety and depressive-like behaviors in OFT and FST, respectively. NCE considerably decreases the malondialdehyde (MDA) and DA levels and IL-6 and TNF-α expressions in mice with schizophrenia-like symptoms. Also, a significant increase is observed in the glutathione (GSH) level and catalase (CAT), superoxide dismutase (SOD), and glutathione reductase (GRx) activity in cerebral tissue. The present study shows that NCE treatment effectively improves KET-induced schizophrenia-like behaviors and oxidative and inflammatory damage. Therefore, NCE, via its bioactive constituents, could have strong neuroprotective effects in the schizophrenia-like model.

Ultrasonic-assisted extraction of a low molecular weight polysaccharide from Nostoc commune Vaucher and its structural characterization and immunomodulatory activity.

In the current study, a novel crude polysaccharide (cNCEP) was extracted from N. commune Vaucher utilizing ultrasonic-assisted extraction (UAE) with 60 % ethanol, employing response surface methodology. The optimal yield of cNCEP was determined to be 8.07 ± 0.08 mg/g, achieved through ultrasonic-assisted extraction under the conditions of a material-to-liquid ratio of 1:22, temperature of 56 °C, power of 570 W, and duration of 147 min. Subsequent purification of NCEP via Sephadex G75 resulted in a novel polysaccharide with a molecular weight of 20.466 kDa. NCEP exhibited significant scavenging activites against DPPH and hydroxyl radicals, as well as notable in vitro immunomodulatory properties. Furthermore, the mechanisms underlying the immunomodulatory effects of NCEP, involving enhancement of immunity, were investigated, revealing potential regulation of MAPK and TLR4-IRF7-NF-κB signaling pathways through RNA-Seq and Western blot analyses. These findings highlight the promising potential of NCEP as an organic immunomodulatory agent and functional food ingredient.

Isolation of biocrust cyanobacteria and evaluation of Cu, Pb, and Zn immobilisation potential for soil restoration and sustainable agriculture.

Soil contamination by heavy metals represents an important environmental and public health problem of global concern. Biocrust-forming cyanobacteria offer promise for heavy metal immobilisation in contaminated soils due to their unique characteristics, including their ability to grow in contaminated soils and produce exopolysaccharides (EPS). However, limited research has analysed the representativeness of cyanobacteria in metal-contaminated soils. Additionally, there is a lack of studies examining how cyanobacteria adaptation to specific environments can impact their metal-binding capacity. To address this research gap, we conducted a study analysing the bacterial communities of cyanobacteria-dominated biocrusts in a contaminated area from South Sardinia (Italy). Additionally, by using two distinct approaches, we isolated three Nostoc commune strains from cyanobacteria-dominated biocrust and we also evaluated their potential to immobilise heavy metals. The first isolation method involved acclimatizing biocrust samples in liquid medium while, in the second method, biocrust samples were directly seeded onto agar plates. The microbial community analysis revealed Cyanobacteria, Bacteroidota, Proteobacteria, and Actinobacteria as the predominant groups, with cyanobacteria representing between 13.3 % and 26.0 % of the total community. Despite belonging to the same species, these strains exhibited different growth rates (1.1-2.2 g L-1 of biomass) and capacities for EPS production (400-1786 mg L-1). The three strains demonstrated a notable ability for metal immobilisation, removing up to 88.9 % of Cu, 86.2 % of Pb, and 45.3 % of Zn from liquid medium. Cyanobacteria EPS production showed a strong correlation with the removal of Cu, indicating its role in facilitating metal immobilisation. Furthermore, differences in Pb immobilisation (40-86.2 %) suggest possible environmental adaptation mechanisms of the strains. This study highlights the promising application of N. commune strains for metal immobilisation in soils, offering a potential bioremediation tool to combat the adverse effects of soil contamination and promote environmental sustainability.

The protective mechanism of a novel polysaccharide from Lactobacillus-fermented Nostoc commune Vauch. on attenuating cadmium-induced kidney injury in mice.

A novel polysaccharide (NCVP-F) from Lactobacillus-fermented Nostoc commune Vauch. was obtained to investigate its underlying mechanism in cadmium-induced kidney injury. Results indicated that in comparison with NCVP, NCVP-F with lower molecular weight of 365.369 kDa, exhibited higher mole percentage of Man and Glc-UA, whereas slightly lower mole percentage of other monosaccharides. NCVP-F is a α-pyran polysaccharide similar to NCVP. Meanwhile, NCVP-F can more effectively alleviate hepatorenal injury (ALT, AST, TG, BUN and SCr) and kidney tissue lesions in Cd-injured mice model by increasing antioxidant enzyme activity (SOD, GSH and GSH-Px), inhibiting cytokines levels (IL-6, IL-1ß, TNF-α and IL-18). In addition, NCVP-F effectively inhibited apoptosis proteins (Bax, cytochrome c, a-caspase-9 and a-caspase-3) and enhanced anti-apoptotic protein (Bcl-2) probably via activating PI3K/AKT/mTOR pathway in the Cd-injury kidney. Furthermore, 16S rRNA sequencing results indicated that NCVP-F better enriched Lachnospiraceae, reduced Muribaculaceae, Alloprevotella and Blautia to regulate Cd-induced gut microbiota disorders, which was probably down-regulated 7 pathways including apoptosis and lipopolysaccharide biosynthesis, and up-regulated 63 pathways, such as carbohydrate metabolism and lipid metabolism. This study suggested that applying functional NCVP-F prepared by biotransformation with low molecular weight might be more beneficial.

Application of composite coating of Nostoc commune Vauch polysaccharides and sodium carboxymethyl cellulose for preservation of salmon fillets.

The spoilage of fish products and the growth of pathogenic bacteria cause great economic loss and serious harm to human health, so fish preservation is very important issue. In this study, Nostoc commune Vauch polysaccharides (NVP) was added into sodium carboxymethyl cellulose (CMC) to form a mixed coating to prepare an active packaging material. The antibacterial and antioxidant activities of NVP, physicochemical properties of the mixed coating, and preservative effects of the coating on salmon fillets were evaluated. The results showed that NVP had good antibacterial and antioxidant activities. Physical characterization of the coating solution showed that when the ratio of NVP to CMC was 1:3, the coating had the best dispersion, denser structure and strongest hydrogen bond. On this basis, NVP/CMC coating can significantly prolong the shelf life of salmon fillets during cold storage by reducing pH, improving the color and texture, delaying the oxidation of fat and protein, inhibiting the growth of microorganisms. At the same time, the coated salmon fillets had good sensory acceptance. The results showed that the edible coating has a broad application prospect in the preservation of fish products.

Effects of in vitro digestion and fermentation of Nostoc commune Vauch. polysaccharides on properties and gut microbiota.

Nostoc commune Vauch. polysaccharides (NCVP) was extracted from Nostoc commune Vauch. with strong biological properties. The molecular weight of NCVPs (NCVP, NCVP-S, NCVP-G, and NCVP-I) exhibited a downward trend, and the molar ratio of constituent monosaccharides of NCVPs significantly changed, implying that NCVP could be degraded under in vitro simulated digestion. The antioxidant activities of NCVPs were significantly improved during in vitro digestion. In addition, NCVPs had a prebiotic effect on Lactobacillus strain. During in vitro fermentation, NCVP was degraded and utilized by the gut microbiota, and a variety of short-chain fatty acids (SCFAs) were formed. Functional gene prediction of 16S rDNA sequencing data inferred that NCVP could promote gut metabolism and improve the body's defense mechanism. Overall, these findings emphasized that NCVP is beneficial by maintaining the gut health and can be used as potential prebiotics in the functional foods and medicine industries.

Structure and enzymatic degradation of the polysaccharide secreted by Nostoc commune.

Noctoc commune is a cyanobacterium living in various and extreme environments. Its ability to survive in desert, on ice or high altitude is explained by its exceptional metabolism and its capacity to resist to desiccation. N. commune cells are embedded in a gelatinous matrix made of polysaccharides which fixes water and participates in maintaining the cells in hydrated conditions. The structure of the polysaccharide of N. commune harvested in Saint Martin d'Uriage (France) and the oligosaccharides obtained after its enzymatic degradation were determined. The repeating unit of the main chain is a tetra-saccharide: [→4)-ß-D-Glcp-(1 â†’ 4)-ß-D-Xylp-(1 â†’ 4)-ß-D-Glcp-(1 â†’ 4)-α-D-Galp-(1→], branched at position 6 of a glucose residue by a ß-linked pyruvated glucuronic acid residue. About 30% of the Xylp residues were branched with a Xylf residue. Comparison of this structure with the polysaccharides secreted by other Nostoc species and strains suggest a strong selection pressure on the structure in agreement with its important biological role.

Anti-Obesity Effect of Nostoc commune Ethanol Extract In Vitro and In Vivo.

Nostoc commune is an edible terrestrial blue-green alga. It has shown many beneficial effects on human health. This study aimed to investigate the phytochemical assay of N. commune ethanol extract (NEE) and its anti-obesity effects. The effect of a high-calorie diet on lipid accumulation in 3T3-L1 preadipocytes is investigated, and a Wistar rat model is used to demonstrate the anti-obesity effect of NEE and its mechanism. The results showed that the NEE has phytochemical compounds, such as total polyphenol, total flavonoids, and total terpenoids. NEE was also shown to suppress cell proliferation and lipid accumulation (26.9%) in 3T3-L1 preadipocytes. Furthermore, NEE reduced the body weight (13.5%), fat tissue weight (13.3%), and the serum FFA (19.4%), TG (14.2%), TC (11.8%), and LDL-C (16.4%) of rats. In histopathology, NEE was shown to diminish the size of adipocytes and hepatic lipid droplets. The NEE downregulated the mRNA expression of adipogenesis (PPAR-γ, SREBP-1c) and lipid lysis-related genes (ATGL, HSL) in epididymal adipose tissue. The NEE also upregulated the mRNA expression of ß-oxidation related genes (AMPK, CPT-1, PPAR-α) in the liver. Overall, this study suggests NEE has the potential to be developed as a functional food for anti-obesity.

Structural characteristics of polysaccharide microcapsules fromNostoc commune,and their applications in skin wound healing and pathological repair.

In this study, the extraction conditions ofNostoc communeVauch polysaccharide (NCVP) were optimized by single factor and orthogonal experiments. Then, the NCVP microcapsules (NCVPM) were prepared. After analyzing the microcapsule structural and thermal characteristics, the skin wound healing ability was studied by establishing back trauma rat models. Results showed that the NCVP yield was 10.37% under the following optimum conditions: 210 min extraction time, solid-liquid ratio of 1:50 and extraction temperature of 90 °C. The overall performance of the microcapsule was the best when the concentration of sodium alginate, calcium chloride and chitosan was 2%, 3% and 0.3%, respectively. NCVPM had spherical morphology, typical microcapsule structural characteristics and good thermal stability, and NCVP was dispersed in the microcapsules. NCVPM showed good biocompatibility and biodegradability, which met the requirements for slow-release polymer materials. After 14 days of treatment, the wound healing rate was 92.4%, the cells were arranged neatly and regularly, the cell nucleus became large and elliptical, the cell had a tendency to divide, and the fibers and microvessel were significantly more. By evaluating the mechanism, NCVPM could increase the content of hydroxyproline and glutathione to protect cells from oxidative damage, leading in turn to accelerated wound healing and shorter wound healing times. It could also accelerate cell division, collagen and microvascular production by increasing transcription levels of vascular endothelial growth factor mRNA and miRNA-21.

Molecular α-relaxation process of exopolysaccharides extracted from Nostoc commune cyanobacteria.

Broadband dielectric spectroscopy was used to investigate the molecular α-relaxation of the exopolysaccharides (EPS) extracted from Nostoc commune cyanobacteria. The EPS were modified in different ways. EPS were carboxymethylated to obtain carboxymethyl-exopolysaccharides (CEPS). EPS and CEPS were doped with ammonium iodide and 1-butyl-3-methylimidazolium chloride. An α relaxation process was observed for all specimens. The temperature dependence of the relaxation times for pure and doped, EPS and CEPS polymers exhibited non-Arrhenius behavior. This relaxation process was associated with the glass transition of the complex heteropolysaccharides produced by the cyanobacteria. The molecular mobility at the glass transition, Tg, was affected by both the carboxymethylation treatment and the doping. The fragility index also decreased for the doped specimens, which may be attributed to an increase in the mobility of the polymer chains due to the plasticizing effect of the doping agents.

Kinetic modeling of the ultrasonic-assisted extraction of polysaccharide from Nostoc commune and physicochemical properties analysis.

Based on the theory of extraction and diffusion of Chinese herbal medicine, the dynamic model of ultrasonic-assisted extraction process of polysaccharide from Nostoc commune Vauch. was established according to the second law of Fick, and further verified at different solid-liquid ratio (1/40-1/80 g/mL), temperature (313.15-353.15 K), ultrasonic power (240-600 W) and extraction time (0-25 min), the dynamic parameters including rate constant and relative extraction rate were respectively analyzed. The rate constant (k) gradually increased with the increase of temperature at different solid-liquid ratio. The maximum concentration of polysaccharide (NCVP) from N. commune was obtained with an optimal extraction condition at solid-liquid ratio of 1:50, extraction temperature of 353.15 K, ultrasonic power of 540 W and extraction time of 25 min. NCVP, the non reducing sugar with typical infrared spectrum characteristics of polysaccharide, dissolves in water but not dissolved in ethanol, acetone and petroleum ether and displays a good stability and smooth surface. The results provide the basis for NCVP in depth theoretical study of polysaccharide extraction processing.

Growth of cyanobacterial soil crusts during diurnal freeze-thaw cycles.

Various Nostoc spp. and related cyanobacteria are able to survive extreme temperatures and are among the most successful colonists of high-elevation sites being exposed due to glacial retreat. It is unclear, however, if cyanobacteria can grow during the extreme freeze-thaw cycles that occur on a year-round basis at high-elevation, peri-glacial sites or if they only grow during the rare periods when freeze-thaw cycles do not occur. We conducted several experiments to determine if cyanobacteria that form biological soil crusts (BSCs) at high-elevation sites (> 5,000 m.a.s.l.) in the Andes can grow during diurnal freeze-thaw cycles on a par with those that occur in the field. Here we show that a soil crust that had been frozen at -20°C for five years was able to increase from 40% to 100% soil coverage during a 45-day incubation during which the soil temperature cycled between -12°C and 26°C every day. In a second, experiment an undeveloped soil with no visible BSCs showed a statistically significant shift in the bacterial community from one containing few cyanobacterial sequences (8% of sequences) to one dominated (27%) by Nostoc, Microcoleus, and Leptolyngbya phylotypes during a 77-day incubation with daily freeze-thaw cycles. In addition, counts of spherical Nostoc-like colonies increased significantly on the soil surface during the experiment, especially in microcosms receiving phosphorus. Taken together these results show that freeze-thaw cycles alone do not limit the growth of BSCs in high-elevation soils, and provide new insight into how life is able to thrive in one of the most extreme terrestrial environments on Earth.

Healthy efficacy of Nostoc commune Vaucher.

Nostoc commune Vaucher, a macroscopic cyanobacterium, has long been appreciated as a healthy food and traditional medicine worldwide. Accumulated evidence has demonstrated that it possesses a wide range of remarkably protective physiological and pharmacological activities, largely based on animal and in vitro studies. In this review, we summarise and update evidence regarding the chemical composition and nutritional characteristics of Nostoc commune Vaucher, and comprehensively discuss the recent studies on the antioxidative, anti-inflammatory, anti-carcinogenic and immune regulation properties of Nostoc commune Vaucher and Nostoc commune Vaucher-derived extracts. The available results demonstrate the potential of it to act as a functional food for the amelioration of human associated diseases. More details from human clinical trials should be a matter of further investigation.

Unusual reversible elastomeric gels from Nostoc commune.

Nostoc commune cyanobacteria grow in extreme conditions of desiccation and nutrient-poor soils. Their colonies form spherical gelatinous bodies are composed of a variety of polysaccharides that allow them to store water and nutrients. In this paper, we study this type of biological gel that shows characteristics of both chemical and physical gels. The structure of this gel was assessed by means of scanning electron microscopy, plate-plate rheometry, Fourier transform infrared spectroscopy and absorption/desorption tests. The storage modulus of this gel was found to be frequency independent, as is usual for chemical gels. The stress sweeps showed a reversible stress softening behaviour that was explained in terms of the physical nature of the interactions of this network. The high density of physical crosslinks probably allows this physical network to behave as a highly elastomeric chemical network, limiting the relaxation of individual chains. On the other hand, reversibility is associated with the physical nature of its bonds.