Screening,Identification and Optimization of Fermentation Condition of an Endophytic Bacteria from Seabuckthorn Nodules with High-yield Exopolysaccharide

Objective:The study was to screen and identify the strain with high-yield exopolysaccharide(EPS)from 6 endophytic bacteria producing of seabuckthorn nodules,and optimize its fermentation conditions. Methods:In order to screen the strain with high-yield of EPS,phenol-sulfuric acid method and DNS method were used to determine EPS production. The strain was identified based on its morphological,physiological and biochemical characteristics and 16S rRNA sequencing analysis. Medium compositions and fermentation conditions were optimized by single-factor test,and medium compositions were further optimized by orthogonal test. Results:A high-yield EPS-producing strain TT207 was screened and identified as Bacillus subtilis. The optimal medium components for EPS production were determined as follows:Sucrose 50 g/L,KNO₃ 10 g/L and KH₂PO₄ 8 g/L. The optimal fermentation conditions for EPS production were determined as follows:Culture time of 48 h,culture temperature of 34℃,initial pH of 6.5,inoculation amount of 4%,bottling amount of 70 mL/250 mL and rotation rate of 140 r/min. Under the optimum conditions,the yield of the EPS was improved by 6.04 times than before. Conclusions:The screened strain of TT207 Bacillus subtilis fermented under the optimized conditions,the yield of the EPS reached 12.39 mg/mL. It was an EPS producing strain with potential for development.