Anti-radiation Activity And Structure Analysis Of Exopolysaccharide Produced By Pantoea Agglomerans KFS

The exopolysaccharide producing strain in this paper was isolated from Redforest of Shenzhen and preserved in our lab. The original experiment showed that thestrain could survive from the strong UV-radiation. A series of high unsattlratedaromatic pigments dissolved in2,3-butanediol (BAPs) were obtained from theextracellular metabolites of strain Pantoea agglomerans KFS, which effectivelyabsorbed UV irradiation ranging from290-340nm and reduced radiation damage.However, the role of the EPS played in the anti-UV radiation was not clarified. In thispaper, the anti-UV radiation activity and the mechanism as well as moisture retentionand absorption abilities in vitro of EPS was conducted at first; Then, the liquidfermentation culture conditions were optimized using the extracellular polysaccharideproduction as an index. The methods of high performance gel permeationchromatography (HPGPC), gas chromatography (GC), enzyme hydrolysis, infraredSpectroscopy and liquid mass spectrometry (LC-MS) were employed to analyze thestructure of the extracellular polysaccharide. The main research contents and resultswere as follows:1. The fermentation conditions of EPS were optimized using statistical methodssingle factor experiments and response surface methodology (RSM) design. As aresult, the optimum cultivation conditions initial pH value, medium volume, inoculumsize, temperature and rotate speed were8.0,100mL/250mL,5%,26℃and190rpmrespectively. The optimized media: sucrose56g/L, peptone3.5g/L, ZnSO40.2g/Land (NH4)2SO43g/L. The maximum yield of EPS was17.03g/L after48h under theseconditions. The strain fermentation curve showed the highest yield24.95g/L appearedat45h. The polysaccharide extraction technology was optimized, the volume of thefermentation liquor was concentrated to1/2, pH was unchanged,1.5times of ethanolwas used to precipitate polysaccharide, then freeze dried to polysaccharide samples.Pure polysaccharide was obtained using Sephacryl S-400HR gel filtration chromatography.2. The molecular weight of the EPS was determined to be756kDa through highgel permeation chromatography method (HPLC). Gas Chromatography analysisrevealed that the polymer was made up of mannose and glucose in the ratio of4:3.Infrared spectroscopy and ESI-LC-MS showed that the polysaccharide wasβ-D-pyranoid configuration contained ethyl pyruvate substituent.3. The anti-UV radiation activity and the mechanism as well as moisture retentionand absorption abilities in vitro of EPS were conducted. The results showed that thatthe EPS was superior to other sources in hygroscopicity, similar to HA and lower toglycerol in moisture retention. The UV-irradiation protective effect on cells of the EPSwas related to the EPS concentration and UV radiation time. Choosing the survivalrate of the E.Coli, C.albicans and S.aureus as arguments, when the UV exposure timecame to5min, the experimental group with4mg/mL EPS were48.49%,36.73%, and47.5%, remarkably higher than the control group at the rate of13.68%,13.47%, and12.25%, respectively. For explaining the mechanism of the anti-UV radiation activity,the antioxidant activity and the UV-absorption ability were measured, respectively.The results showed that the EPS showed significant scavenging abilities to DPPHradical, hydroxyl radical and superoxide radical with EC50values of7.8mg mL-15.4mg mL-1, and40mg mL-1, respectively. There was no UV absorbtion during280-380nm. These data suggested that EPS might protect bacteria from UV-induced damageby scavenging the ROS. Therefore, the EPS as a natural moisturizer and anti-radiationmaterial had a widely application prospects.