除生物固氮功能外，固氮菌通常还有促进植物生长的作用。近年来对非豆科植物来源的联合固氮菌进行固氮和促生功能的改造和利用成为热点。本研究以联合固氮菌Kosakonia radicincitans GXGL-4A为对象，接种黄瓜苗根际，考察其对根际土中氮素含量和形态转化及土壤酶活的影响；同时，采用宏基因组技术对根际微生物群落结构组成和丰度变化进行监测；利用宏转录组技术检测固氮菌施用后不同时期（早期和后期）土壤中GXGL-4A菌株的氮代谢相关基因的表达差异，明确调控根际氮循环的关键基因。建立GXGL-4A的Tn5转座突变株库，筛选对黄瓜苗促生作用统计学上显著缺失和显著提高的突变株，并与野生株GXGL-4A间进行差异转录组分析和发酵液促生成分的质谱分析比较，鉴定出与促生效应密切相关的功能基因和促生物质，解析该菌对植物的促生机制，为今后研究固氮菌与植物间的互作及微生物肥料开发奠定理论基础。

In addition to biological nitrogen fixation, the nitrogen-fixing (NF) bacteria usually promote plant growth. Recently, the genetic modification and utilization of NF bacteria from non-leguminous plants aimed at improving the nitrogen fixation capacity and plant promoting effect has become a hot spot. The nitrogen content and morphological transformation rule, and the enzyme activities in the cucumber rhizosphere soil will be investigated by the inoculation of an associative NF bacterial strain Kosakonia radicincitans GXGL-4A on the rhizosphere of cucumber seedlings in this study. Meanwhile, a metagenomic analysis should be performed to monitor the composition of rhizosphere microbial community and the variation of colony abundance. After inoculation, the expression levels of nitrogen metabolism-related genes of GXGL-4A at different stages (early and late) will be compared by metatranscriptomic sequencing, and the key genes regulating nitrogen cycling in rhizosphere could be identified. A Tn5 insertional mutant library of GXGL-4A will be established to screen the mutants with a statistically significant absence or a significant improvement in plant growth-promoting effects on cucumber seedlings. In order to identify the functional genes closely associated with plant growth-promoting effect and the growth-promoting active substances, and further exploring the promotion mechanism of GXGL-4A on plant growth, the comparisons of differential transcriptome and mass spectrometry analysis of the growth promoting components in fermentation broth between the target mutants and the wild type strain GXGL-4A will be carried out. All these results are expected to lay a theoretical foundation for the study of the interaction between nitrogen-fixing bacteria and plants and the development of microbial fertilizer in the forthcoming future.