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Branched architecture of fucoidans (sulfated fucose-rich polysaccharides) gained considerable interest in recent years in view of the effect of this branching on fucoidan’s biological activity. The aim of this work was to characterize the branching architecture of the pristine and hydrolyzed fucoidan macromolecules of the marine seaweed Fucus vesiculosus. We studied the influence of the duration of acidic hydrolysis on the fucoidan macromolecules. The structure-sensitive ratios of macromolecular radii, obtained by dynamic and static (SLS) light scattering, and capillary viscometry corresponded to spherical form of the macromolecules, indicating their branched architecture. The structure-sensitive ratios were analyzed with respect to the molecular weight distributions obtained by size-exclusion chromatography. The Kratky representation of the angular dependences of SLS intensity provided a spectacular evidence for the fucoidans’ branching. For the first time, the fucoidans’ branching was characterized quantitatively by fitting the scattering form factor developed for hyperbranched macromolecules. Under acidic hydrolysis, the molecular mass and size of the fucoidan macromolecules decreased, but the globular form of macromolecules remained unchanged. Upon increasing the time of the acidic hydrolysis, the ζ-potential of the fucoidans changed from − 14 to − 27 mV. The hydrolyzed fucoidans, in turn, exhibited pronounced polyelectrolyte expansion in aqueous solutions when compared with the unhydrolyzed one.

Simple Summary The continuous emergence of new pathogenic strains of bacteria resistant to antibiotics highlights the importance of search for the new natural sources of antimicrobial compounds. Fucoidans, sulfated polysaccharides from the cell walls of brown algae, attract the attention of many researchers due to their wide range of biological activities. Being natural and practically non-toxic, they are considered as a promising antimicrobial component that could, where possible, replace the use of strong chemical antiseptics and modern antibiotics. Natural fucoidans are polydisperse polysaccharides whose composition can vary greatly depending on the species, habitat, as well as on the way of purification. In this work, we investigate the structure and antibacterial properties of fucoidans from the brown algae Fucus vesiculosus gathered in the littoral of the Barents Sea. These fucoidans appear to have a significant bacteriostatic effect on the growth of four tested bacterial strains. Such an effect was more pronounced for crude fucoidan samples that did not undergo additional steps of purification. Abstract Fucoidans, sulfated polysaccharides found in cell walls of brown algae, are considered as a promising antimicrobial component for various applications in medicine and the food industry. In this study, we compare the antibacterial properties of two fractions of fucoidan from the brown algae Fucus vesiculosus gathered in the littoral of the Barents Sea and sampled at different stages of purification. The crude fraction of fucoidan was isolated from algae by extraction with aqueous ethanol and sonication. The purified fraction was obtained by additional treatment of the crude fraction with a solution of calcium chloride. The structural features of both fractions were characterized in detail and their antibacterial effects against several Gram-positive and Gram-negative bacteria were compared by photometry, acridine orange staining assay, and atomic force microscopy. Fucoidan inhibited growth in all of the above microorganisms, showing a bacteriostatic effect with minimum inhibitory concentrations (MIC) in the range between 4 and 6 mg/mL, with E. coli being the most sensitive to both fractions. Changes in the chemical composition after treatment of the crude fraction with a solution of calcium chloride led to a decrease in the content of sulfates and uronic acids and diminished antibacterial activity.

The aim of this study was to compare the effects of sulfated fucopolysaccharides isolated from Fucus vesiculosus on HeLa G-63, Hep G2, and Chang liver cells. Native fucoidan F3 and two fractions (F3-0.5 and F3-1) obtained by anion-exchange chromatography were analyzed using chemical methods and IR spectroscopy. It was demonstrated that F3 and F3-1 are characterized by a higher content of sulfates, location of sulfo groups mostly at the C4 atom of fucose residue, and low content of uronic acids inhibited cell proliferation. Human liver carcinoma Hep G2 appeared to be the most sensitive to fucoidan, whereas nonmalignant human Chang liver cells were the least sensitive.

Enzymes capable of modifying the sulfated polymeric molecule of fucoidan are mainly produced by different groups of marine organisms: invertebrates, bacteria, and also some fungi. We have discovered and identified a new strain of filamentous fungus Fusarium proliferatum LE1 (deposition number in Russian Collection of Agricultural Microorganisms is RCAM02409), which is a potential producer of fucoidan-degrading enzymes. The strain LE1 (RCAM02409) was identified on the basis of morphological characteristics and analysis of ITS sequences of ribosomal DNA. During submerged cultivation of F. proliferatum LE1 in the nutrient medium containing natural fucoidan sources (the mixture of brown algae Laminaria digitata and Fucus vesiculosus), enzymic activities of α-L-fucosidase and arylsulfatase were inducible. These enzymes hydrolyzed model substrates, para-nitrophenyl α-L-fucopyranoside and para-nitrophenyl sulfate, respectively. However, the α-L-fucosidase is appeared to be a secreted enzyme while the arylsulfatase was an intracellular one. No detectable fucoidanase activity was found during F. proliferatum LE1 growth in submerged culture or in a static one. Comparative screening for fucoidanase/arylsulfatase/α-L-fucosidase activities among several related Fusarium strains showed a uniqueness of F. proliferatum LE1 to produce arylsulfatase and α-L-fucosidase enzymes. Apart them, the strain was shown to produce other glycoside hydrolyses.