Study On The Characteristics And Synthesis Of Extracellular Polysaccharide Produced By Sclerotium Rolfsii With Carbon Sources

As an extracellular polysaccharide(EPS)produced by some species of Sclerotium rolfsii,scleroglucan is widely used in petroleum,chemical industry,food and other fields due to its good thickening and moisturizing properties.However,its cost is too high due to its low utilization rate of carbon source.At present,the synthesis mechanism of the EPS is not clear,so it is necessary to explore the synthesis pathway of the EPS.In this paper,the laboratory preserved strain Sclerotium rolfsii(ATCC 15205)was used to study the viscosity and yield of the EPS produced by this fungi under different carbon sources,which confirmed the influence of carbon sources on the yield and viscosity of polysaccharide.Transcriptome and proteomics sequencing results revealed the influence of carbon sources on key genes and enzymes in the process of polysaccharide synthesis,and provided a basis for exploring the pathway of the EPS synthesis of Sclerotium sp.At first,glucose,sucrose,maltose,galactose,lactose,arabinose,xylose and fructose were used as carbon sources separately to ferment the Sclerotium rolfsii under the same conditions.After 72 hours,the fermentation broth was collected and then homogenized,filtered,precipitated by alcohol,removed impurity and redissolved the extracellular polysaccharides(EPS)to obtain a certain concentration of polysaccharide solution.At the same concentration,the viscosity and yield differences of eight EPSs were analysed.Three kinds of EPSs were selected which fermented with glucose,sucrose and lactose as carbon sources,and named as SEPS(high yield and viscosity),GEPS(medium yield and viscosity)and LEPS(low yield and low viscosity)respectively.Furthermore,the fermentation results showed that SEPS group and GEPS group were significantly higher than LEPS group in yield,carbon utilization rate and biomass of mycelium,and the pH of SEPS group and GEPS group is lower(more oxalic acid production).Then,the differently expressed genes(DEG)and gene functions related to the synthesis of the three EPSs were compared and mined by means of transcriptomics.Functional enrichment analysis showed that the DEG in the three groups were significantly related to the functions of "cell process","metabolic process","catalytic activity" and"binding";in the groups of LEPS vs.SEPS and LEPS vs.GEPS,the DEG were related to cell metabolism and redox process.In LEPS group,most of the genes involved in glycolysis/gluconeogenesis,steroid biosynthesis,phenylalanine metabolism,alkaloid biosynthesis and cytochrome P450’s effect on metabolism of exogenous substances were down regulated,while those involved in ribosome metabolism,endoplasmic reticulum protein processing,valine,leucine and isoleucine degradation,fatty acid degradation,andβ-alanine metabolism were up regulated.The DEG’s expression of UTP-glucose-1phosphouridine transferase and UDP-glucose pyrophosphorylase(UGP),which determine the synthesis of UDP-glucose and glucuronic acid in polysaccharide molecules of Sclerotium rolfsii,was higher in GEPS and SEPS groups than in LEPS group,but the gene expression of 1,3-β-d-glucanase was up regulated in LEPS group.Proteomic data also confirmed the results.Finally,the production of polysaccharide was improved up to 159%by increasing the expression of alcohol dehydrogenase,acetyl CoA synthetase,fructose diphosphate aldolase and nitrate reductase.The paper was proved that the carbon source has an effect on the yield and characteristics of polysaccharides,and it opens up a way to increase the yield of EPS by adding precursors,which provides a theoretical basis for the study of the mechanism of EPS’s synthesis.