Screening Of Novel Exopolysaccharide-producing Bacteria And Exploring The Structure Of It’s EPS

Extracellular polysaccharides have been drawing attention because of the advantages of high security, short production period and good economical benefit. A variety of extracellular polysaccharide products has been applied in many fields such as food, medicine, industry and environmental protection etc. Screening of novel exopolysaccharide-producing bacteria and discovering new EPS are prerequisites for their practical applications. This paper aims to find novel bacteria which can secrete EPS with potential applicability, at the same time, to increase EPS productivity by optimizing culture conditions.In this paper, five exopolysaccharide-producing bacteria were screened out by the selective medium method (first screen) and the flask-shaking method (rescreening). Among of them, the bacterium which was obtained from the soil of Sanqing Mountain broadleaf forests,Shangrao City, Jiangxi Province can produce more polysaccharides than others within a same period. And it was determined to be a new species of Paenibacillus after several testing such as microscopy tests, Gram stain tests, biochemical tests and the sequences comparing with the strain of16S rDNA, denoted as Paenibacillus sp.44051.Phylogenetic tree was constructed based on16SrRNA.Paenibacillus sp.44051was cultivated by flask-shaking and experiments were carried on by single factor test. The results show that the optimal carbon source and nitrogen source of the strain are soluble starch (4%) and KN03(0.2%).The optimum fermentation conditions are: initial pH value7.0, temperature30℃, broth volume50mL/250mL, inoculum size of10%, exponential phase in3-36h, stationary phase in36-78h, decline phase after78h. The strain with using soluble starch produced acid product in the end, which resulted in a gradually decreasing pH value from7.0to5.8within96h.The yield of EPS reached1.46%after fermentation78h.The chemical compositions of the EPS are74.05%sugar,4.21%moisture,10.67%ash and11.07%protein and other impurities; Solubility of the polysaccharide in hot water is0.683g/100gH20; The viscosity of EPS decreases with increasing temperature, it is only34mPa.s at80℃.The refined EPS was obtained by the following steps:(i) precipitation with ethanol,(ii) deproteinization with HCl reagent,(iii) dialysis,(iv)freeze-drying. The Thin-layer chromatography (TLC) analysis revealed that the Polysaccharide was composed only one monosaccharide, probably mannose. Fourier Transform infrared spectroscopy showed that the conformation of polysaccharides is a-pyranoside bond type. In summary, Paenibacillus sp.44051has the advantage of high production efficiency of EPS, simple culture conditions, fast growth and low cost of fermentation. The EPS obtained from Paenibacillus sp.44051shows high viscosity, nontoxic, easy to extract and separate and it has great potential to be applied in fields of industry and health drugs.