Table_3_Endophytic nitrogen-fixing bacteria DX120E inoculation altered the carbon and nitrogen metabolism in sugarcane.XLSX

Endophytic nitrogen-fixing bacteria are versatile and widely distributed in plants. Numerous strains of endophytic nitrogen-fixing bacteria are used as biofertilizers to minimize the utilization of chemical fertilizers, improve nutrient use efficiency, increase crop productivity, and reduce environmental pollution. However, the mechanism underlying the interaction between nitrogen-fixing bacteria and plants is still unclear. So, the present study was planned to assess the effects of endophytic nitrogen-fixing bacteria on sugarcane by analyzing the changes in physiological and biochemical activities. In the current study, Klebsiella variicola DX120E, an endophytic nitrogen-fixing bacterium, was inoculated on sugarcane varieties B8 and ROC22 to evaluate the effects on nitrogen and carbon metabolism-related enzymatic activity and biomass. Results showed that DX120E inoculation improved the enzymatic activities related to gluconeogenesis and nitrogen metabolism increased the sugarcane plant’s height, cane juice Brix, biomass, chlorophyll, and soluble sugar content in sugarcane. Metabolomics analysis revealed that the metabolome modules were highly enriched in carbon and nitrogen metabolic pathways of strain-affected sugarcane than uninoculated control. The identified carbohydrates were associated with the glycolysis or gluconeogenesis and tricarboxylic acid (TCA) cycle in plants. Metabolomic profiling in the present investigation showed that carbohydrate metabolism is coordinated with nitrogen metabolism to provide carbon skeletons and energy to amino acid synthesis, and amino acid degradation results in several metabolites used by the citric acid cycle as an energy source. Moreover, differentially expressed metabolites of non-proteinogenic amino acids have a further complementary role to the action of endophytic nitrogen-fixing bacteria. Meanwhile, a significant difference in metabolites and metabolic pathways present in stems and leaves of B8 and ROC22 varieties was found. This study discovered the potential benefits of DX120E in sugarcane and suggested candidate regulatory elements to enhance interactions between nitrogen-fixing microbes and sugarcane.

内生固氮菌（Endophytic nitrogen-fixing bacteria）功能多样且广泛分布于植物体内。诸多内生固氮菌菌株被用作生物肥料（biofertilizers），用以减少化学肥料的施用、提升养分利用效率、提高作物产量并降低环境污染。然而，固氮菌与植物间的互作机制仍未阐明。为此，本研究拟通过分析生理生化活性变化，探究内生固氮菌对甘蔗的影响。本研究选取内生固氮菌变栖克雷伯氏菌DX120E（Klebsiella variicola DX120E），将其接种于甘蔗品种B8与ROC22，以评估其对氮、碳代谢相关酶活性及生物量的影响。结果显示，接种DX120E可提升糖异生（gluconeogenesis）及氮代谢相关的酶活性，同时提高甘蔗株高、蔗汁锤度、生物量、叶绿素含量与可溶性糖含量。代谢组学分析表明，相较于未接种的对照组，经菌株处理的甘蔗其代谢组模块在碳、氮代谢通路中显著富集。本研究鉴定出的碳水化合物与植物的糖酵解、糖异生及三羧酸（TCA）循环密切相关。本次代谢组学分析结果显示，碳水化合物代谢与氮代谢相互协同，可为氨基酸合成提供碳骨架与能量；而氨基酸降解则会产生多种可作为柠檬酸循环能量来源的代谢物。此外，非蛋白氨基酸（non-proteinogenic amino acids）类差异代谢物可进一步辅助内生固氮菌发挥功能。同时，B8与ROC22两个甘蔗品种的茎、叶组织中，代谢物与代谢通路均存在显著差异。本研究揭示了DX120E在甘蔗种植中的潜在应用价值，并提出了可强化固氮微生物与甘蔗互作的候选调控靶点。