Structure And Characteristics Of Welan Gum Fermented By Sphingomonas Sp.from Nitrogen Sources And Transcriptomic Analysis

Welan gum,one of the most market prospective microbial polysaccharides developed by an American company C P Kelco,is produced by Sphingomonas sp.Due to the excellent rheological properties of welan gum aqueous media,it is widely used in the construction of concrete industry and oilfield drilling.This research studied the determination method of bacterium concentration and the fermentation kinetics model using the strainSphingomonas sp.ATCC 31555 stored in the laboratory.Afterwards,the yield and viscosity from different nitrogen source medium were compared.Furthermore,the nature difference of welan gum was revealed through measuring the welan gum structure.The determination of transcriptome level was expected to lay a foundation for revealing the influence of nitrogen source mediumon the production of welan gum.The main contents of this study are as follows:(1)The amount of bacteriain fermentation fluid was indirectly calculated by measuring the concentration of N-acetyl glucosamine in the fermentation broth based on the correlation between glucosamine and cell volume.The results showed that the amount of bacteria in the fermentation fluid could be determined exactly by measuring the amount of welan gum fermentation fluid.Meanwhile,the kinetics model for describing the Sphingomonas sp.ATCC 31555 growth,nitrogen source consumption and the welan gum production was obtained utilizing the dynamic parameters which from the existing fermentation data.The experimental and dynamic model results demonstrated that the calculated value of the mathematical model fits well with the results of the fermentation experiment and provided the basis for further studying the process of welan gum produced by Sphingomonas sp.ATCC 31555 fermentation.(2)The influence of welan gum structure from inorganic nitrogen source and organic nitrogen was studied.Results showed the yield of welan gumin inorganic nitrogen source was less than that in organic nitrogen source,while the molecular weight of wellan gum was larger.Mannose content in weilan gum was relatively high,while glucuronic acid content and acetyl content were low.Scanning electron microscopy showed that the intermolecular connections of welan gum were more denser.Overall,these results indicated that the viscosity of welan gum solution in inorganic nitrogen source were higher than that of inorganic nitrogen source.The shear dilute value(n)was also smaller.(3)The influence of compound nitrogen source on the welan gumrheological properties was investigated by studying the different ratio of compound nitrogen sources of NaNO3 medium and beef paste medium.The results revealed that the viscosity,heat resistanceand salt tolerance of welan gum were increased with the increase of NaNO3 ratioin nitrogen source.The viscosity,elastic modulus(G1)and elastic modulus(G2)of welan gum procuced by three kinds of nitrogen sources were stable in the condition of pH 2 to pH 10 and all kinds of salt ions,while these above indicators were decreased in the condition of strong acid,especially strong alkali.The viscosity of welan gum was decreased with the elevation of temperature,while the decreased range of viscosity was diminished when the temperature reached to 120?.The dynamic modulus of welan gum remained stable in the process of temperature rised from 90? to 140?,and the G1 value was always higher than the G2 value.(4)The effects of different nitrogen sources on gene expression and function of Sphingomonassp.ATCC 31555 strain were studied,and the changes of strains transcripts from different nitrogen source cultures were also analyzed.The results suggested that both the yield of welan gum and bacterial biomassin organic nitrogen source(ON)group and compound nitrogen source(CN)group were significantly higher than that of inorganic nitrogen source(IN)group.The DEGs in the three groups were significantly correlated with the process of metabolic and signal transduction based on transcriptome sequencing data and functional enrichment analysis.DEGs between IN and CN group were predicted to be associated with bacterial chemotaxis.Similarly,DEGs between ON and CN group were also associated with bacterial chemotaxis.Moreover,DEGs of key enzymes participated in the production of welan gum were identified.The gene expressions of phosphoglucose isomerase(PGI),phosphoglucose translocation enzyme(PGM),UDP-glucose 4-epimerase(UGE),UDP-glucose pyrophosphorylase(UGP)and UDP-glucose dehydrogenase(UGD)in organic nitrogen source group were higher than that in inorganic nitrogen source group.However,the gene expressions of mannose-phosphate isomerase(PMI)and acetylase(SAT)in inorganic nitrogen source group were higher than that in organic nitrogen source group.