Lopez-Lara I M, Orgambide G, Dazzo F B, Olivares J, Toro N
Department of Microbiology, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Cientificas, Granada, Spain.
J Bacteriol. 1993 May;175(10):2826-32. doi: 10.1128/jb.175.10.2826-2832.1993.
Rhizobium sp. wild-type strain GRH2 was originally isolated from root nodules of the leguminous tree Acacia cyanophylla and has a broad host range which includes herbaceous legumes, e.g., Trifolium spp. We examined the extracellular exopolysaccharides (EPSs) produced by strain GRH2 and found three independent glycosidic structures: a high-molecular-weight acidic heteropolysaccharide which is very similar to the acidic EPS produced by Rhizobium leguminosarum biovar trifolii ANU843, a low-molecular-weight native heterooligosaccharide resembling a dimer of the repeat unit of the high-molecular-weight EPS, and low-molecular-weight neutral beta (1,2)-glucans. A Tn5 insertion mutant derivative of GRH2 (exo-57) that fails to form acidic heteropolysaccharides was obtained. This Exo- mutant formed nitrogen-fixing nodules on Acacia plants but infected a smaller proportion of cells in the central zone of the nodules than did wild-type GRH2. In addition, the exo-57 mutant failed to nodulate several herbaceous legume hosts that are nodulated by wild-type strain GRH2.
根瘤菌属野生型菌株GRH2最初是从豆科树木蓝叶金合欢的根瘤中分离出来的，具有广泛的宿主范围，包括草本豆科植物，如三叶草属。我们研究了GRH2菌株产生的细胞外胞外多糖（EPS），发现了三种独立的糖苷结构：一种高分子量酸性杂多糖，与豆科根瘤菌生物变种三叶草ANU843产生的酸性EPS非常相似；一种低分子量天然杂寡糖，类似于高分子量EPS重复单元的二聚体；以及低分子量中性β(1,2)-葡聚糖。获得了GRH2的一个Tn5插入突变体衍生物（exo-57），该突变体不能形成酸性杂多糖。这个Exo-突变体在金合欢植物上形成了固氮根瘤，但与野生型GRH2相比，它感染根瘤中央区细胞的比例较小。此外，exo-57突变体不能在野生型菌株GRH2能结瘤的几种草本豆科宿主上结瘤。
