Lerner Anat, Okon Yaacov, Burdman Saul
Department of Plant Pathology and Microbiology and The Otto Warburg Center for Agricultural Biotechnology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
Microbiology (Reading). 2009 Mar;155(Pt 3):791-804. doi: 10.1099/mic.0.021824-0.
Several genes involved in the interaction between Azospirillum brasilense Sp7 and plants are located on the pRhico plasmid. Here we report the characterization of an Sp7 mutant strain with impairment of the pRhico-located gene wzm. This gene encodes an inner-membrane component of an ATP-binding cassette (ABC) transporter with similarity to transporters involved in surface polysaccharide export. Indeed, SDS-PAGE revealed that LPS synthesis is affected in the wzm mutant. No significant differences were observed between wild-type and mutant strains in exopolysaccharide (EPS) amount; however, several differences were observed between them in EPS monosaccharide composition, and only wild-type colonies stained positively with Congo red. Microscopy revealed that wzm mutant cells are longer and thinner, and exhibit several differences in their cell surface relative to the wild-type. The wzm mutant was more resistant to oxidative stress, starvation, desiccation, heat and osmotic shock than the wild-type. In contrast, the mutant was more susceptible than the wild-type to UV radiation and saline stress. The strains also differed in their susceptibility to different antibiotics. Differences between the strains were also observed in their outer-membrane protein composition. No differences were observed between strains in their ability to attach to sweet corn roots and seeds, and to promote growth under the tested conditions. As LPS plays an important role in cell envelope structural integrity, we propose that the pleiotropic phenotypic changes observed in the wzm mutant are due to its altered LPS relative to the wild-type.
几种参与巴西固氮螺菌Sp7与植物相互作用的基因位于pRhico质粒上。在此，我们报告了一个位于pRhico上的基因wzm功能受损的Sp7突变菌株的特征。该基因编码一种ATP结合盒（ABC）转运蛋白的内膜组分，与参与表面多糖输出的转运蛋白相似。实际上，SDS-PAGE显示wzm突变体中脂多糖（LPS）的合成受到影响。野生型和突变菌株在外多糖（EPS）量上未观察到显著差异；然而，它们在EPS单糖组成上存在一些差异，并且只有野生型菌落用刚果红染色呈阳性。显微镜观察显示，wzm突变体细胞更长更细，并且相对于野生型，其细胞表面存在一些差异。wzm突变体比野生型对氧化应激、饥饿、干燥、热和渗透压休克更具抗性。相反，该突变体比野生型对紫外线辐射和盐胁迫更敏感。这些菌株对不同抗生素的敏感性也有所不同。在它们的外膜蛋白组成上也观察到菌株之间的差异。在测试条件下，菌株在附着于甜玉米根和种子以及促进生长的能力方面未观察到差异。由于LPS在细胞包膜结构完整性中起重要作用，我们认为在wzm突变体中观察到的多效性表型变化是由于其相对于野生型改变的LPS所致。
