Leigh J A, Reed J W, Hanks J F, Hirsch A M, Walker G C
Department of Microbiology, University of Washington, Seattle 98195.
Cell. 1987 Nov 20;51(4):579-87. doi: 10.1016/0092-8674(87)90127-9.
We have identified a set of Tn5-generated mutants of Rhizobium meliloti on the basis of their failure to form a fluorescent halo under UV light when grown on agar medium containing Calcofluor. These mutations define a new genetic locus we have termed exoH. Alfalfa seedlings inoculated with exoH mutants form ineffective nodules that do not contain intracellular bacteria or bacteroids. Root hair curling is significantly delayed and infection threads abort in the nodule cortex. Analyses of exopolysaccharide secreted by exoH mutants have shown that it is identical to the Calcofluor-binding exopolysaccharide secreted by the exoH+ parental strain except for the fact that it completely lacks the succinyl modification. In vitro translation of total RNA isolated from nodules induced by an exoH mutant has shown that only one of the plant-encoded nodulins is induced, as compared with the 17 nodulins induced by wild-type strains. These observations suggest that succinylation of the bacterial polysaccharide is important for its role(s) in nodule invasion and possibly nodule development.
我们已经鉴定出一组由Tn5诱变产生的苜蓿根瘤菌突变体，其依据是这些突变体在含有荧光增白剂的琼脂培养基上生长时，在紫外光下无法形成荧光晕圈。这些突变定义了一个新的基因座，我们将其命名为exoH。用exoH突变体接种的苜蓿幼苗形成无效根瘤，其中不含细胞内细菌或类菌体。根毛卷曲明显延迟，感染丝在根瘤皮层中停止发育。对exoH突变体分泌的胞外多糖的分析表明，它与exoH+亲本菌株分泌的与荧光增白剂结合的胞外多糖相同，只是完全缺乏琥珀酰修饰。对由exoH突变体诱导形成的根瘤中分离出的总RNA进行体外翻译表明，与野生型菌株诱导的17种根瘤蛋白相比，只有一种植物编码的根瘤蛋白被诱导。这些观察结果表明，细菌多糖的琥珀酰化对于其在根瘤侵染以及可能在根瘤发育中的作用很重要。
