| Microbial polysaccharide WL-26was produced by submerged fermentation of strainsSphingomonas sp. ZJ01and the fermentation condition was optimized on the basis of solutionviscosity and yield of WL-26. The effect of rotational speed and dissolved oxygenconcentration on fermentation were evaluated in shake flasks and3L bioreactor respectively.In order to release the high efficiency production of microbial polysaccharide WL-26, a seriesof strategies was carried out including culture conditions, culture methods and metaboliccharacteristics. After purification the structure and characteristics of WL-26was analyzed.The main contents in this study are as follows:(1) Sucrose, NaNO3and beef extract were the optimal carbon and complex nitrogen sourcesrespectively and the optimal medium consisted of50g/L sucrose,4g/L complex nitrogen(20%NaNO3and80%beef extract),2g/L KH2PO4and0.1g/L MgSO4. Yield ofmicrobial polysaccharide WL-26reached22g/L under the following conditions: mediuminitial pH7.0,5%inoculation volume,1:5aeration ratio (medium volume: flask volume,50mL medium in250mL flask), cultured at200r/min,30oC for58h.(2) Base on the characteristics of Sphingomonas sp. fermentation processes in shake flask and3-L B. Braun Biostat C stainless steel reactor, through optimization of pH control strategy,the concentration of KH2PO4is reduced from2g/L to0.8g/L. This result is significantlyreduced the problem faced on the follow-up step of isolation and purification of WL-26and wastewater treatment, WL-26yield reached27g/L which was increased23%compared with yield in shake flask through multi-stage agitation speed control, carbonfed-batch fermentation, and low concentration of phosphate by adjusting the buffer pH7.0using0.2mmol NaOH.(3) The relations between viscosity and shear rate, concentration, temperature, pH, highpressure, freezing-thawing, cold stored, and salt were evaluated by determining thedynamic and static viscosity. Results showed that the water solution of microbialpolysaccharide WL-26is a typical pseudoplastic liquid, having high viscosity at lowconcentrations. Novel Microbial exopolysaccharides WL-26has been shown attractiveapplication prospect due to its high temperature stability, pH tolerance, and environmentfriendly properties. More and more researches have been focused on production andapplication of it.(4) A new oligosaccharide F21was obtained by microbial polysaccharide WL-26hydrolyzedby0.2M trifuluoroacetic acid and applied on gel-filtration chromatography column(Sephacryl S100). UV scan showed no proteins and nucleic acids and detection of infrared spectra indicated sugar characteristic group in F21.The molecular weight of F21was1280Da evaluated by Esi and F21was composed ofL-rhamnose, D-glucose, D-mannose, D-galactose，and glucuronic acid in a molar ratio of3:1.7:1:1:0.7determined by HPAEC-PAD. Methylation analysis of F21showed that the1,4,6-tri-substituted glucose,1,4-di-substituted rhamnose,1,3-di-substituted glucose and1,4-di-substituted mannose are the main chain, with minor amounts of1,3-di-substitutedrhamnose, terminal glucose and rhamnose residues. The galactose residues arecompletely distributed at non-reducing terminals, and possibly with a glucuronic acidresidue at the other non-reducing terminal by NMR analysis. The proposal structure asfollows:These results provide new soliol scientific data and for further develpment ofpolysaccharide WL-26from Sphingomonas sp.ZJ01and laid a good foundation for the futuredevelpment and application based on the polysaccharide. |
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