Wang Xing, Guo Naijiang, Zhang Yao, Wang Gejiao, Liao Shuijiao, Shi Kaixiang
National Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, P. R. China.
College of Chemistry, Huazhong Agricultural University, Wuhan 430070, P. R. China.
J Exp Bot. 2025 Jun 28. doi: 10.1093/jxb/eraf290.
Maintaining a stable symbiotic relationship between rhizobia and soybeans is important in agriculture and ecosystems. However, cadmium (Cd) pollution disrupts this mutualism's delicate balance. We investigated the protective role of non-nitrogen-fixing bacteria on soybeans under Cd-induced stress. Here, we have identified three Cd-immobilizing bacteria, namely Arthrobacter sp. CC3, Pseudarthrobacter sp. CC12, and Mesorhizobium sp. CC13. These bacteria reduced the bioavailable Cd content in the soil, decreased Cd accumulation in soybeans, and increased nodule nitrogenase activity. However, no nitrogenase genes were identified in the genomes of these three bacterial strains. Soil metabolomics was used to investigate the mechanisms by which these three bacteria enhanced soybean nitrogenase activity. The levels of octanoic acid, propafenone, and levonorgestrel were increased following the introduction of Cd-tolerant bacterial strains. Subsequent soybean pot experiments demonstrated these strains' ability to enhance nodule nitrogenase activity and reduce Cd content in soybeans. The analysis of bacterial abundance in harvested soybean nodules revealed a significant decline in the Bradyrhizobium population, accompanied by a notable increase in Xanthobacteraceae abundance. Co-inoculation with Ancylobacter sp. QY-1, a bacterium belonging to the Xanthobacteraceae family, and Bradyrhizobium sp. USDA110 resulted in enhanced nitrogenase activity in soybean root nodules. Our findings reveal a cooperative mechanism wherein both non-nitrogen-fixing bacteria and specific compounds support soybeans' nitrogen-fixation function under Cd stress by regulating bioavailable Cd and rhizobia abundance. Surprisingly, we also found that the synthetic compounds propafenone and levonorgestrel can confer Cd-stress protection to plants.
维持根瘤菌与大豆之间稳定的共生关系在农业和生态系统中至关重要。然而，镉（Cd）污染破坏了这种共生关系的微妙平衡。我们研究了非固氮细菌在镉诱导胁迫下对大豆的保护作用。在此，我们鉴定出三种镉固定细菌，即节杆菌属CC3、假节杆菌属CC12和中慢生根瘤菌属CC13。这些细菌降低了土壤中生物可利用的镉含量，减少了大豆中的镉积累，并提高了根瘤固氮酶活性。然而，在这三种细菌菌株的基因组中未鉴定到固氮酶基因。利用土壤代谢组学研究这三种细菌增强大豆固氮酶活性的机制。引入耐镉细菌菌株后，辛酸、普罗帕酮和左炔诺孕酮的水平升高。随后的大豆盆栽实验证明了这些菌株增强根瘤固氮酶活性和降低大豆中镉含量的能力。对收获的大豆根瘤中细菌丰度的分析表明，慢生根瘤菌种群显著下降，同时黄杆菌科丰度显著增加。将黄杆菌科的一种细菌Ancylobacter sp. QY-1与慢生根瘤菌属USDA110共同接种，可提高大豆根瘤中的固氮酶活性。我们的研究结果揭示了一种合作机制，即非固氮细菌和特定化合物通过调节生物可利用的镉和根瘤菌丰度，在镉胁迫下支持大豆的固氮功能。令人惊讶的是，我们还发现合成化合物普罗帕酮和左炔诺孕酮可以赋予植物镉胁迫保护作用。
