| Marine is a unique complex ecosystem which contains rich biological resources. Owing to the extreme and special living environment, marine microorganisms have formed a special metabolic mechanism and pathway which can produce extracellular polysaccharides with novel structures and functions. In this paper, the novel extracellular polysaccharides were obtained from the fermented broth of four marine-derived microorganisms, and their physicochemical properties, structural characterizations and antioxidant properties were investigated. The results were as follows:1. An extracellular polysaccharide Ms4-1 was isolated from the fermented broth of the salt-tolerant fungus Cladosporium cladosporioides OUCMDZ-2713 from Yellow River delta salt layer soil, and purified by Q Sepharose Fast Flow anion-exchange chromatography and Sephacryl S-100 gel-permeation chromatography. HPGPC and HPLC analyses indicated that the molecular weight of Ms4-1 was about 19.8 kDa, and Ms4-1 was composed of Man, GlcN, GlcUA, GalNAc, Glc and Gal in a molar ratio of 0.4:0.4:1.0:1.5:2.0:0.2. The partial acid hydrolysis, methylation, ESI-CID-MS/MS and 1D,2D NMR analyses indicated that the main chain of Ms4-1 was mainly composed of a core of five sugars which contained →3)-β-D-GlcpUA(1→, →4)-β-D-GlcpUA(1→ and →3)-α-D-GalpNAc(1→, and a long chain of glucopyranose. The long chain of glucopyranose was attached to the core of five sugars at C-3 positions of →3)-β-D-GlcpUA(1→ residues. The glucopyranose chain consisted of →4)-α-D-Glcp(1→. Ms4-1 exhibited a high antioxidant activity in vitro, and the EC50 values of Ms4-1 for DPPH, superoxide and hydroxyl radicals were about 1.06 mg/mL,0.21 mg/mL and 0.58 mg/mL, respectively. The results showed that Ms4-1 was a heteropolysaccharide with antioxidant activity and novel structure. The study supplied a novel marine extracellular polysaccharide for the "marine polysaccharides database".2. Two extracellular polysaccharides Pwl-land Psl-1 were isolated from the fermented broth of the mangrove soil fungus Aspergillus versicolor PJX-9 and purified by Q Sepharose Fast Flow anion-exchange chromatography and Sephacryl S-100 gel-permeation chromatography. The HPGPC analysis indicated that the molecular weights of Pwl-land Psl-1 were 12.3 kDa and 13.6 kDa, respectively. The HPLC analysis showed that Pwl-land Psl-1 had similar monosaccharide composition, they were mainly composed of Man with a small amount of Glc and Gal, with the molar ratio of 9.3:1.3:1.0 and 6.4:1.1:2.1, respectively. The methylation analysis demonstrated that the chain of Pwl-1 mainly consisted of (1→2)-Manp. In addition, Pwl-1 contained small amounts of (1→6)-Manp, (1→6)-Glcp, (1→2,6)-Manp, Manp(1→and Galf(1→. The EC50 values of Pwl-1 for DPPH, superoxide and hydroxyl radicals were about 3.39 mg/mL,1.50 mg/mL and 1.72 mg/mL, respectively.3. Two extracellular polysaccharides Awl-land Asl-1 were isolated from the fermented broth of the cattail-associated fungus A-154, and purified by Q Sepharose Fast Flow anion-exchange chromatography and Sephacryl S-100 gel-permeation chromatography. The molecular weights of Awl-1 and Asl-1 were 11.7 kDa and 6.6 kDa, respectively. The HPLC analysis showed that Awl-1 was mainly composed of Man and Gal, with a molar ratio of 14.1:1.0. The methylation analysis demonstrated that Awl-1 mainly consisted of Manp(1→, (1→6)-Manp and (1→2,3)-Manp, with small amounts of Galf(1→ and (1→2)-Manp. The EC50 values of Awl-1 for DPPH, superoxide and hydroxyl radicals were about 3.0 mg/mL,1.21 mg/mL and 1.50 mg/mL, respectively.4. Four extracellular polysaccharides Fwl-1, Fsl-1, Fs2-1 and Fs3-1 were isolated from the fermented broth of the mangrove endophytic fungus Aspergillus sp. FJ-6, and purified by Q Sepharose Fast Flow anion-exchange chromatography and Sephacryl S-100 gel-permeation chromatography. The molecular weights of Fwl-1, Fsl-1, Fs2-1 and Fs3-1 were 11.9 kDa,17.2 kDa,16.4 kDa and 18.2 kDa, respectively. Fwl-1 mainly consisted of Man with small amounts of Glc and Gal which was in the molar ratio of 5.2:1.4:1.0. The methylation analysis demonstrated that Fwl-1 contained a large number of (1→2)-Manp, (1→4)-Glcp and (1→2,3)-Manp, small amounts of (1→6)-Manp, Manp(1→ and Galf(1→, and a minor amount of Glcp (1→. The presence of (1→2,3)-Manp indicated that Fwl-1 was a high branched extracellular polysaccharide, and the branch points were in the C-3 positions of (1→2)-Manp residues. Fwl-1 had a novel structure which was rarely found in marine fungi. The EC50 values of Fwl-1 for DPPH, superoxide and hydroxyl radicals were about 3.60 mg/mL,1.21 mg/mL and 1.64 mg/mL, respectively.The investigation provided novel marine extracellular polysaccharides for the "marine polysaccharides database", had potential value and important reference meanings for further research and development of extracellular polysaccharides from marine microorganisms. |
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