中文摘要：

从费氏中华根瘤菌WGF03的基因组中克隆出与胞外多糖分泌密切相关的基因exoD,研究该基因对胞外多糖合成、菌株共生结瘤能力和固氮效率的影响。利用自杀性质粒pK18mobsacB,通过同源双交换法构建exoD基因的缺失突变体ΔexoD。实验发现：与野生菌株相比,突变株在YMA培养基平板上胞外多糖产量明显减少、运动能力也有所减弱;在NaCl浓度小于350 mmol/L范围内,菌体均能维持稳定生长;接种于大豆幼苗后,产生的根瘤数量较多,但个体小、形状不一,且固氮酶活也显著下降。研究结果说明exoD基因参与S.fredii WGF03胞外多糖的合成并影响菌株共生结瘤能力和固氮效率。

英文摘要：

An extracellular polysaccharide secretion related gene exoD was cloned from genome of S. fredii WGF03 and the influence of genes on extracellular polysaccharide synthesis as well as nodulation, nitrogen fixation with host plant was investigated. AexoD mutant was constructed through homologous double-crossover using suicide plasmid pk18mobsacB as a vector. Compared with the wile type strain, the mutant strain produced less exopolysaecharides （EPS） on YMA medium plate and the motility was decreased. Nothing changes in the growth situation on the medium containing less than 350 mmol/L of NaCl. The plant test showed that the number of nodules was more, but small, varying shapes, and nitrogen-fixing enzyme activity was also significantly decreased after inoculation mutant strain. This demonstrated that exoD gene affect EPS synthesis in S. fredii WGF03, and involve in nodulation and nitrogenase activity.