Study On Structure And Antioxidant Properties Of Exopolysaccharides Produced By Marine Fungi

Marine contains abundant microbial resources, especially the microorganismsfrom the mangrove ecosystem and river estuaries ecosystem. The marinemicroorganisms often produce extracellular polysaccharides with novel structures anddiverse biological activities due to their specific marine environment. The novelactive extracellular polysaccharides from marine microorganisms hold a greatpotential application in biology and pharmacology. In the paper, the chemicalcomposition, structure and antioxidant activity in vitro of the extracellularpolysaccharide isolated from the fermented broth of five different marine fungi wereinvestigated. The results are as follows:1. Crude extracellular polysaccharides, LN, LD and PJX, are obtained from thefermented broth of mangrove root mud fungi Aspergillus terreus W-8,Aspergillus flavipes ZHN1-09, and PJX-2, and purified by Q-Sepharose Fast Flowcolumn, Surperdex-75and Sephacryl S-100column. The five purified polysaccharide,designated lnw-c, ds2-2, ds4-1, jxw-2and jxs-2, were obtained. Monosaccharidecomposition analysis by reversed–phase HPLC show that lnw-c contains GlcN, Manand Glc with a ratio of2:1:1, and is an alkaline polysaccharide. Other extracellularpolysaccharides contain high proportion of Man and small amounts of Glc, Gal orGalA. jxw-2and jxs-2are both neutral sugar with a purity of more than90%, andtheir molecular weights are5.6and9.7kDa, respectively. The results of IR spectraand methylation analysis demonstrated that jxw-2, jxs-2and ds2-2mainly containfour kinds of linkage type units: Man(1→,→2)Man(1→,→6)Man(1→, and→2,6)Man(1→. Except the units of mannose,→6)Glc(1→and→2,6)Glc(1→arealso found in lnw-c.2. Two extracellular polysaccharides, yw-2and yss, are obtained from thefermented broth of Aspergillus terreus OUCMDZ-1925, and obtained by Q-SepharoseFast Flow ion-exchange chromatography and Sephacryl S-100gel permeation chromatography. Chemical and HPGPC analyses indicated that yss was ahomogeneous polysaccharide with a molecular weight of18.6kDa. Monosaccharidecompositions analysis by reversed-phase HPLC showed that yss was composed ofMan and Gal in a molar ratio of7.70:1.00. Infrared spectroscopy combined withmethylation and two-dimensional nuclear magnetic resonance (NMR) analysesdemonstrated that yss is a high branched polysaccharide. The main chain mainlyconsists of→2)-α-D-Manp(1→with small amount of→6)-α-D-Manp(1→. Thebranch chains→1)-α-D-Manp(6→1)-α-D-Manp and β-D-Galf(1→are linked to theC-6of→2)-α-D-Manp(1→of main chain. This study firstly isolated a novel highbranched galactoglucomannan with main chain of→2)-α-D-Manp(1→and→6)-α-D-Manp(1→from Barracuda splanchnic fungus Aspergillus terreus. Theresults suggested that symbiotic fungi of marine organisms could be a potential sourceof polysaccharides with novel structures.3. Crude extracellular polysaccharide YQ is isolated from the fermentation liquidof fungus Penicillium sp. H-25-02, Four extracellular polysaccharides, qw-2, qs1-1,qs-2s and qs-3a are obtained by Q-Sepharose Fast Flow ion exchange column andSephacryl S-100gel permeation chromatography. Chemical composition and HPGPCanalysis showed that all the sugars content of the polysaccharide components aremore than89%, and the molecular weights of qw-2, qs1-1, qs-2s and qs-3a are12.22,16.17,20.96,22.87kDa, respectively. Monosaccharide compositions analysis byreversed-phase HPLC showed that the qs1-1, qs-2s and qs-3a are acidicpolysaccharides, and they are mainly composed of Man with a small amount of GalA.IR and methylation analyses indictated that the four extracellular polysaccharide withdiversiform structures, and the qs-2s and qs-3a with rare→6)Galf(1→. Units→6)Galf(1→and Galf(1→locate at side chains of qs-2s by the study of partial acidhydrolysis.4. Preliminary antioxidant activity screening experiments in vitro of7~8kinds ofpolysaccharides by radicals DPPH, superoxide anoin and hydroxyl radical are carriedout. It is found that all these samples had certain free radicals scavenging abilities.EPSs qs-2s, qs-3a, yss and ds4-1with the EC50values of3.5,5.0,2.8and1.0mg/mL have a better DPPH scavenging activities than others, qs-2s, yss and jxs-2have a EC50values of3.5,3.8and6.0mg/mL, and qs-3a with a maximum clearance of46%.Besides, the maximum clearances of all the samples to superoxide anion are no morethan50%. In0~8.0mg/mL, free radical scavenging abilities of samples areconcentration dependence, the clearance of samples increase with the increasedconcentration of the sample.This paper accumulates original data for the research of extracellularpolysaccharides of marine fungi, provides new structures of fungal polysaccharidesfor the "marine polysaccharides database" in China, applies material sourses forseeking polysaccharide with antioxidant activities, and establishes the basis for furtherdevelopment of extracellular polysaccharide products from marine microorganism.