产胞外多糖罗汉果内生菌的筛选及其发酵条件优化

该研究利用α-萘酚-硫酸法和苯酚-硫酸法从罗汉果中筛选产胞外多糖的内生菌株，采用形态观察、生理生化试验及分子生物学技术对其进行菌种鉴定，并采用单因素和正交试验对其产胞外多糖的发酵条件进行优化。结果表明，筛选到一株产胞外多糖的罗汉果内生菌株，编号为LHG-3，并被鉴定为韦德曼尼芽孢杆菌（Bacillus wiedmannii）。菌株LHG-3产胞外多糖的最佳培养基为超级肉汤（TB）培养基，在此基础上，经优化得出最优发酵条件为蔗糖2.5%、尿素1.2%、氯化钙0.4%、pH值7.0、接种量8%，在30 ℃条件下培养42 h后，胞外多糖产量达到（1.59±0.03）mg/mL，是优化前的1.9倍。

Screening of extracellular polysaccharide-producing strains from endophytic bacteria of Siraitia grosvenorii and fermentation conditions optimization

In this study, the extracellular polysaccharide-producing endophyte was screened from Siraitia grosvenorii by α-naphthol-sulfuric acid method and phenol-sulfuric acid method, and identified by morphological observation, physiological and biochemical tests and molecular biology techniques. The fermentation conditions for the extracellular polysaccharide-producing strain were optimized by single factor and orthogonal experiments. The results showed that a extracellular polysaccharide-producing endophyte was screened, named LHG-3, and identified as Bacillus wiedmannii. The optimal medium for the strain LHG-3 was terrific broth (TB) medium. Based on this, the optimum conditions were sucrose 2.5%, urea 1.2%, calcium chloride 0.4%, pH 7.0 and inoculum 8%. The production of extracellular polysaccharide reached (1.59±0.03) mg/ml at 30 ℃ for 42 h, which was 1.9 times higher than that before optimization.