Structural Characterization And Bioactivities Of Exopolysaccharides Produced By Two Microbes With Different Sources

The unique physical and chemical properties of microbial exopolysaccharides have been harnessed for its wide use in food and pharmaceutical industries for promoting health effects.Microbial exopolysaccharides as a kind of biological macromolecules,which have many types,complex structures,and significant microbial diversity and differences.Moreover,most microbial exopolysaccharides resources and their physical and chemical properties and applications have not been developed and studied in depth.Therefore,screening and isolating new microorganisms and studying the composition,structure,and biological activity of the polysaccharides produced by them have great research significance for developing new microbial polysaccharide resources and obtaining microbial polysaccharides and they've derived biologically active substances with potential applications.In this paper,two strains producing extracellular polysaccharides were selected from nature and identified as Bacillus licheniformis and Fusarium merismoides.While optimizing the extraction conditions of the two strains to produce EPS,the extracellular crude polysaccharides were also separated and purified,and their components and biological activities were analyzed.The main research contents of the paper are as follows:(1)In this work,a new type of water-soluble exopolysaccharides(EPS)was isolated from Bacillus licheniformis(B.licheniformis).Firstly,response surface methodology(RSM),based on a three-level,three-factor,was used to determine optimum conditions for EPS extraction.And RSM analysis indicated optimum condition was at the temperature of 8°C for 10.44 hours with ethanol at a concentration of 79.22%(v/v),the maximum yield of EPS was 3.07 g/m L.Secondly,EPS were seperated using DEAE-Sepharose Fast Flow column chromatography and acquired two polysaccharide fractions,BL-P1 and BL-P2.BL-P1 had larger molecular weight than BL-P2 from structural analyses,because of higher content of mannose,ribose,glucuronic acid,galactose,arabinose and fructose in BL-P2.Moreover,the characterization of BL-P1 and BL-P2 was investigated with Fourier transform infrared spectroscopy(FT-IR)and nuclear magnetic resonance(NMR)spectroscopy,the results indicated that EPS was mainly composed of?3)-?-D-Galp-(1?,?3,5)-?-L-Araf-(1?,?3)-?-D-Glcp-(1?,?-D-Glcp-(1?and?4)-?-L-Fucp-(1?4)-?-D-Xylp-(1?4)-?-L-Rhap(1?3)-?-D-Manp-(4? residues.In vitro antioxidant activity assay,EPS exhibited potent quenching capacities on hydroxyl and 1,1-diphenyl-2-picrylhydrazyl(DPPH)radicals in a dose-dependent manner.Furthermore,BL-P2 had higher activity than BL-P1 in inhibiting ?-amylase and ?-glucosidase.which would have potential to be applied in nutraceutical and pharmaceutical industries.(2)In this work,a new type of exopolysaccharide secreted by Fusarium merismoides A6(FM-EPS)was isolated and the extraction conditions were optimized by a response surface methodology(RSM).Two fractions of F.merismoides A6 exopolysaccharides(FM-ESP1 and FM-EPS2)were obtained using DEAE-Sepharose Fast-Flow column chromatography.As indicated by monosaccharide composition analysis,both fractions mainly consisted of mannose,glucose,galactose,and ribose,with average molecular weight(Mw)of 5.14×104 and 6.50×104 g/mo L,respectively.FT-IR and NMR spectroscopy indicated the FM-ESPs were mainly composed of ?5)-?-D-Galp-(1?,?2)-?-D-Glcp-(1?,?-D-Galf-(1?and ?4)-?-L-Fucp-(1?4)-?-L-Rhap-(1?6)-?-D-Manp-(1? residues.Moreover,in vitro antioxidant and antiproliferative activities assays proved that FM-EPSs had good antioxidant and anti-proliferation activities on He La and Hep G2 cells.FM-EPS1 showed stronger antioxidant activities than FM-EPS2.However,FM-EPS2 showed the strongest anti-proliferation activity.Therefore,B.licheniformis and F.merismoides A6 exopolysaccharides could be explored as potential antioxidant and anticancer agent applied in the food,cosmetics and pharmaceutical industries.