Data_Sheet_1_Isolation and Characterization of High-Efficiency Rhizobia From Western Kenya Nodulating With Common Bean.docx

Common bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhouse experiments, common bean plants inoculated with two isolates, B3 and S2 in sterile vermiculite, performed better than those inoculated with CIAT899 or plants grown with nitrogen fertilizer alone. In contrast to CIAT899, both isolates grew in the media with pH 4.8. Furthermore, isolate B3 had higher phosphate solubilization ability and produced more indole acetic acid than the other two rhizobia. Genome analyses revealed that B3 and S2 are different strains of Rhizobium phaseoli. We recommend fieldwork studies in Kenyan soils to test the efficacy of the two isolates in the natural environment in an effort to produce inoculants specific for these soils.

普通菜豆是第三世界国家的主要蛋白质来源之一。它们可与固氮根瘤菌（nitrogen-fixing rhizobia）形成根瘤，而这些根瘤菌必须适配当地土壤。农业生产中常使用诸如热带根瘤菌（Rhizobium tropici）CIAT899这类商用根瘤菌菌株。然而，由于当地土壤pH值偏低，该菌株在包括肯尼亚在内的诸多地区均未能显著提升普通菜豆的产量。我们从肯尼亚西部两块从未施用商用接种剂的普通菜豆根瘤中，分离得到两株土著根瘤菌。随后我们测定了这两株菌在普通菜豆中的固氮能力、溶磷能力以及吲哚乙酸（indole acetic acid）合成能力。在温室试验中，在无菌蛭石基质中接种B3与S2两株分离菌的普通菜豆植株，其生长表现优于接种CIAT899的植株，以及仅施用氮肥的植株。与CIAT899不同的是，两株分离菌均可在pH 4.8的培养基中生长。此外，分离菌B3的溶磷能力更强，且相较于另外两株根瘤菌可合成更多吲哚乙酸。基因组分析表明，B3与S2均为菜豆根瘤菌（Rhizobium phaseoli）的不同菌株。我们建议在肯尼亚土壤中开展田间试验，以验证这两株分离菌在自然环境中的接种效果，进而开发适配当地土壤的专用接种剂。