Dazzo F B, Hubbell D H
Appl Microbiol. 1975 Dec;30(6):1017-33. doi: 10.1128/am.30.6.1017-1033.1975.
Cross-reactive antigens of clover roots and Rhizobium trifolii were detected on their cell surfaces by tube agglutination, immunofluorescent, and radioimmunoassay techniques. Anti-clover root antiserum had a higher agglutinating titer with infective strains of R. trifolii than with noninfective strains. The root antiserum previously adsorbed with noninfective R. trifolii cells remained reactive only with infective cells, including infective revertants. When adsorbed with infective cells, the root antiserum was reactive with neither infective nor noninfective cells. Other Rhizobium species incapable of infecting clover did not demonstrate surface antigens cross-reactive with clover. Radioimmunoassay indicated twice as much antigenic cross-reactivity of clover roots and R. trifolii 403 (infective) than R. trifolii Bart A (noninfective). Immunofluorescence with anti-R. trifolii (infective) antiserum was detected on the exposed surface of the root epidermal cells and diminished at the root meristem. The immunofluorescent crossreaction on clover roots was totally removed by adsorption of anti-R. trifolii (infective) antiserum with encapsulated infective cells but not with noninfective cells. The cross-reactive capsular antigens from R. trifolii strains were extracted and purified. The ability of these antigens to induce clover root hair deformation was much greater when they were obtained from the infective than noninfective strains. The cross-reactive capsular antigen of R. trifolii 403 was characterized as a high-molecular-weight (greater than 4.6 times 10(6) daltons), beta-linked, acidic heteropolysaccharide containing 2-deoxyglucose, galactose, glucose, and glucuronic acid. A soluble, nondialyzable, substance (clover lectin) capable of binding to the cross-reactive antigen and agglutinating only infective cells of R. trifolii was extracted from white clover seeds. This lectin was sensitive to heat, Pronase, and trypsin. inhibition studies indicated that 2-deoxyglucose was the most probable haptenic determinant of the cross-reactive capsular antigen capable of binding to the root antiserum and the clover lectin. A model is proposed suggesting the preferential adsorption of infective versus noninfective cells of R. trifolii on the surface of clover roots by a cross-bridging of their common surface antigens with a multivalent clover lectin.
通过试管凝集、免疫荧光和放射免疫测定技术，在三叶草根和三叶草根瘤菌的细胞表面检测到了交叉反应抗原。抗三叶草根抗血清对三叶草根瘤菌感染菌株的凝集效价比非感染菌株更高。先前用非感染性三叶草根瘤菌细胞吸附过的根抗血清，仅对包括感染性回复突变体在内的感染性细胞仍有反应。当用感染性细胞吸附时，根抗血清对感染性和非感染性细胞均无反应。其他不能感染三叶草的根瘤菌物种未显示出与三叶草有交叉反应的表面抗原。放射免疫测定表明，三叶草根与三叶草根瘤菌403（感染性）的抗原交叉反应性是非感染性的三叶草根瘤菌Bart A的两倍。用抗三叶草根瘤菌（感染性）抗血清进行免疫荧光检测，在根表皮细胞的暴露表面可检测到，而在根分生组织处则减弱。用包被的感染性细胞吸附抗三叶草根瘤菌（感染性）抗血清后，三叶草根上的免疫荧光交叉反应完全消除，但用非感染性细胞吸附则无此效果。从三叶草根瘤菌菌株中提取并纯化了交叉反应性荚膜抗原。当这些抗原从感染性菌株而非非感染性菌株中获得时，它们诱导三叶草根毛变形的能力要强得多。三叶草根瘤菌403的交叉反应性荚膜抗原被鉴定为一种高分子量（大于4.6×10⁶道尔顿）、β-连接的酸性杂多糖，含有2-脱氧葡萄糖、半乳糖、葡萄糖和葡萄糖醛酸。从白三叶草种子中提取出一种可溶性、不可透析的物质（三叶草凝集素），它能够结合交叉反应抗原并仅凝集三叶草根瘤菌的感染性细胞。这种凝集素对热、链霉蛋白酶和胰蛋白酶敏感。抑制研究表明，2-脱氧葡萄糖最有可能是能够与根抗血清和三叶草凝集素结合的交叉反应性荚膜抗原的半抗原决定簇。提出了一个模型，表明三叶草根瘤菌的感染性细胞与非感染性细胞通过其共同表面抗原与多价三叶草凝集素的交叉桥接而优先吸附在三叶草根部表面。
