Abstract: The soil bacterium L20309 with production capacity of extracellular polysaccharide was isolated from the prunus divaricata in Daxigou of Xinjiang and the fermentation conditions were optimized. Results showed that the better carbon and nitrogen sources for it to produce extracellular polysaccharide were glucose and peptone, and the optimal mass concentrations of carbon and nitrogen sources were 20 g/L and 30 g/L, respectively. The optimal growth conditions were pH 8.0 of the medium, the loading sample of 500 mL/L, the inoculum of 5% of 28℃. When cultured under such condition for 72 h, the polysaccharide product could reach to 2.562 μg/mL.

Key words: soil bacterium, extracellular polysaccharide, medium composition, fermentation