Inoculation with Rhizobium tropici and Rhizobium freirei can partially supply the nitrogen demand required for normal development and high productivity of common bean (Phaseolus vulgaris L.). Here, a simple and low-cost approach was used to select R. tropici sodium azide-resistant mutants with improved efficiency as microsymbiont of common bean. We mutagenized R. tropici CIAT889 by treatment with methyl methanesulfonate (MMS) and selected azide-resistant mutants. Six mutants (AzR14, AzR15, AzR16, AzR17, AzR18, and AzR19) with varying levels of resistance were obtained and characterized for symbiotic traits and performance upon inoculation of common bean. Mutants grew and produced exopolysaccharides similar to the CIAT899 wildtype; however, swarming motility, biofilm, and auxin production were altered. About nodulation, shoot biomass, and nitrogen content, the performance of mutant strains was improved or similar to that of CIAT899. All mutants enhanced nodulation of common bean; furthermore, AzR14, AzR18, and AzR19 increased nodule biomass by 25%–36%. AzR18 and AzR19 increased shoot biomass by up to 13% compared to CIAT899, whereas AzR14, AzR15, AzR16, and AzR17 reduced biomass accumulation by 9%–19%. In addition, AzR18 and AzR19 showed higher motility or biofilm production than the other mutant strains, suggesting that these traits are involved in bacterial symbiotic effectiveness. Shoot N content do not differ between plants inoculated with the CIAT899 or mutant strains, although plants inoculated with AzR18, AzR19 and CIAT899 had increased the shoot N as compared to uninoculated plants grown at N-limiting conditions. Our results demonstrated the possibility to improve the performance of the R. tropici microsymbiont through induced mutagenesis followed by the selection of azide resistant mutants. This approach allowed to identify the AzR18 and AzR19 strains, which showed superior nodulation and symbiotic effectiveness than CIAT899 while providing equivalent amounts of N to the inoculated plants. We propose the AzR18 and AzR19 as promising candidates for developing new and more efficient inoculants for common bean, nevertheless further trials under field conditions are required to confirm their superior performance to the wild strain.

接种热带根瘤菌和弗氏根瘤菌可以部分满足普通豆（菜豆）的正常发育和高生产率所需的氮需求。在这里，使用一种简单且低成本的方法来选择具有提高效率的热带罗非鱼抗叠氮菜突变体作为普通豆的微共生体。我们诱变了热带罗非鱼CIAT889通过用甲磺酸甲酯（MMS）处理并选择了抗叠氮化物的突变体。获得了具有不同抗性水平的六个突变体（AzR14，AzR15，AzR16，AzR17，AzR18和AzR19），并针对普通豆接种后的共生特性和性能进行了表征。突变体生长并产生类似于CIAT899野生型的胞外多糖。但是，蜂群运动，生物膜和植物生长素的产生发生了变化。关于结瘤，枝条生物量和氮含量，突变菌株的性能提高或与CIAT899相似。所有的突变体都增强了普通豆的根瘤形成。此外，AzR14，AzR18和AzR19使根瘤生物量增加了25％–36％。与CIAT899相比，AzR18和AzR19可将枝条生物量提高多达13％，而AzR14，AzR15，AzR16和AzR17则可减少9％–19％的生物量积累。此外，AzR18和AzR19显示出比其他突变菌株更高的运动性或生物膜产生，表明这些性状与细菌共生功效有关。接种CIAT899或突变株的植物之间的苗N含量没有差异，尽管与在N限制条件下生长的未接种植物相比，接种AzR18，AzR19和CIAT899的植物已增加了苗N。我们的结果表明，有可能改善电池的性能 与在氮限制条件下生长的未接种植物相比，AzR19和CIAT899增加了芽N。我们的结果表明，有可能改善电池的性能 与在氮限制条件下生长的未接种植物相比，AzR19和CIAT899增加了芽N。我们的结果表明，有可能改善电池的性能tropic R. tropici microsymbiont通过诱变，然后选择抗叠氮化物的突变体。这种方法可以鉴定AzR18和AzR19菌株，它们显示出比CIAT899更好的结瘤和共生功效，同时为接种的植物提供等量的N。我们建议将AzR18和AzR19用作开发新的和更有效的普通豆接种剂的有希望的候选者，尽管如此，仍需要在田间条件下进行进一步试验，以确认它们对野生菌株的优越性能。