Riccillo P M, Collavino M M, Grasso D H, England R, de Bruijn F J, Aguilar O M
Instituto de Bioquímica y Biología Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Argentina.
Mol Plant Microbe Interact. 2000 Nov;13(11):1228-36. doi: 10.1094/MPMI.2000.13.11.1228.
Rhizobium tropici strain CIAT899 displays a high intrinsic thermal tolerance, and had been used in this work to study the molecular basis of bacterial responses to high temperature. We generated a collection of R. tropici CIAT899 mutants affected in thermal tolerance using TnS-luxAB mutagenesis and described the characterization of a mutant strain, CIAT899-10T, that fails to grow under conditions of high temperature. Strain CIAT899-10T carries a single transposon insertion in a gene showing a high degree of similarity with the guaB gene of Escherichia coli and other organisms, encoding the enzyme inosine monophosphate dehydrogenase. The guaB strain CIAT899-10T does not require guanine for growth due to an alternative pathway via xanthine dehydrogenase and, phenotypically, in addition to the thermal sensitivity, the mutant is also defective in symbiosis with beans, forming nodules that lack rhizobial content. Guanine and its precursors restore wild-type tolerance to grow at high temperature. Our data show that, in R. tropici, the production of guanine via inosine monophosphate dehydrogenase is essential for growth at extreme temperatures and for effective nodulation.
热带根瘤菌CIAT899菌株具有很高的内在耐热性，本研究利用该菌株探究细菌对高温响应的分子基础。我们通过TnS-luxAB诱变技术构建了一系列耐热性受影响的热带根瘤菌CIAT899突变体，并对其中一个在高温条件下无法生长的突变菌株CIAT899-10T进行了表征。CIAT899-10T菌株在一个与大肠杆菌及其他生物的guaB基因高度相似的基因中存在单个转座子插入，该基因编码肌苷单磷酸脱氢酶。由于存在通过黄嘌呤脱氢酶的替代途径，guaB突变菌株CIAT899-10T生长不需要鸟嘌呤，并且在表型上，除了热敏感性外，该突变体在与豆类共生时也存在缺陷，形成的根瘤中缺乏根瘤菌成分。鸟嘌呤及其前体可恢复野生型在高温下生长的耐受性。我们的数据表明，在热带根瘤菌中，通过肌苷单磷酸脱氢酶产生鸟嘌呤对于在极端温度下生长和有效结瘤至关重要。
