· Molecular Microbiology Research, 2025, Vol.15, No.1, 37-44 http://microbescipublisher.com/index.php/mmr 39 example, scientists have conducted in-depth research on the genome of Sinorhizobium fredii and discovered many key genes related to nitrogen fixation (Contador et al., 2020). Genetic differences between different species of Rhizobium (such as Bradyrhizobium, Rhizobium, Mesorhizobium) will also affect their cooperative effectiveness and nitrogen fixation ability (Nakei et al., 2022). 3.3 Non-dominant Rhizobium strains and nitrogen fixation efficiency Some rhizobia (non-dominant strains) that are not the "main force" perform better in difficult environments. Studies have found that some newly isolated strains can help soybeans develop effective nodules under high nitrate conditions better than traditional strains (such as Bradyrhizobium diazoefficiens USDA110) (Ni et al., 2024). For example, several strains (USDA110, NKS4, NKM2, NKTG2) were placed in a nitrate environment of different concentrations (0, 5, 12.5, 20 mM), and it was found that the nodule morphology and number of them formed at the soybean roots vary greatly. In an environment of 0 mM nitrate, all strains can cause soybeans to grow many nodules, and the distribution is relatively uniform, and nitrogen fixation is not inhibited. When the nitrate concentration increases to 5 mM, non-dominant strains such as NKM2 and NKTG2 still form pink nodules, which means there is active hemoglobin inside and the nitrogen fixation function is still there. However, the number of traditional USDA110 nodules has decreased, and the nitrogen fixation capacity has decreased. At two higher nitrate concentrations, 12.5 and 20 mM, USDA110 has fewer nodules, most of which are yellow or orange in color, indicating that nitrogen fixation is basically inhibited. NKM2 and NKTG2 can still form many pink nodules, indicating that they are very adaptable and have good nitrogen fixation function (Figure 1) (Nguyen et al., 2019). Figure 1 Roots of G. max cv. enrei inoculated with the rhizobial strains (Adopted from Nguyen et al., 2019) 4 Techniques for Improving Soybean-Rhizobium Interactions 4.1 Strain improvement and engineering breeding If you want soybeans and rhizobia to "cooperate" better, one way is to improve the strains or use genetic breeding to improve their genetic characteristics. This makes them easier to fix nitrogen. Through genome research, scientists have found many key genes. These genes are related to drought resistance and nitrogen fixation. For example, some special genes were found in the Rhizobium sp. R1 and R. cellularosilyticum R3 strains that help soybeans germinate smoothly during drought (Igiehon et al., 2019). In addition, the metabolic process of Sinorhizobium fredii was simulated and some important genes that control nitrogen fixation were found. This also
RkJQdWJsaXNoZXIy MjQ4ODYzNA==