一株产胞外多糖新菌株Escherichia hermannii的分离筛选及鉴定

Screening,isolation and identification of a new exopolysaccharide-producing strain from Escherichia hermannii

在江苏省无锡市一处农田蔬菜地的土样中筛选到一株新型产胞外多糖的细菌，在以葡萄糖为底物的YM琼脂培养基上生长良好，菌落白色光滑，有粘性。在以蔗糖为底物的多糖发酵培养液中好氧培养72h后，培养液有粘度。发酵液中加入酒精，发现有类似多糖的纤维沉淀出现，沉淀物经洗涤、烘干、粉碎得多糖粗产物，其总糖含量为（32±0．2）％。用水重新溶解多糖粗产物，在较低浓度时即有可观的粘度，具有潜在的商业应用价值。通过16SrDNA序列分析法对筛选的新菌株进行分子生物学鉴定，结果表明该菌株为一株新的赫氏埃希菌，并命名为Escherichia hermanniiXPF-1。利用透射电子显微镜观察菌体形态，细胞呈圆直杆状，细胞平均大小约为（0．9-1．0）（1.4-1.

A new strain of exopolysaccharide-producing bacterium was screened and isolated from soil sample of a vegeta- ble field in Wuxi, Jiangsu Province. This strain was found to grow very well on glucose-based YM agar plates as creamy white mucoid colonies and produced viscous broth in the sucrose-based polysaceharide fermentation medium after 72 h. Ethanol addition to the viscous fermentation broth resulted in polysaccharide-like fibrous precipitate which was recovered, dried and milled. The crude polysaccharide material contained an average of （32 ＋ 0.2） % total sugar by phenol-sulfuric acid assay. Solutions of the resulting powder exhibited viscosities relative to its concentration suggesting potential industrial applications. Taxonomic identification of the bacterial isolate by 16S rDNA sequencing indicated a new strain of Escherich- ia hermannii and designated as Escherichia hermannii strain XPF-1. Its transmission electron micrographs indicated that the bacterium exhibited a straight cylindrical rod shape. The average bacterial cell dimension was determined to be （0.9- 1.0）×μm×（1.4-1.8）×μm.