本课题拟从胞内、胞外和全局系统全面揭示氧化镁对L-乳酸生物合成的强化机理。首先，通过高浓度镁离子压力下Lactobacillus rhamnosus LA-04-1转录组学分析，探索转录与产酸效率的关联规律，确定镁离子影响的靶向位点，在转录水平揭示产物合成的强化机理；其次，基于代谢组学对高浓度镁离子胁迫下的菌体进行代谢通量分析，确定菌体代谢与L-乳酸合成的关联规律，定位关键代谢节点，阐释镁离子对产物代谢合成的强化规律；此外，研究回用氧化镁特殊微环境对L-乳酸合成的影响，揭示菌体、底物、产物与微环境之间的分配、扩散和空间位阻效应及其互作规律，并进行特异元素分析，确证回用氧化镁对L-乳酸合成的促进机理；最后，在系统集成基础上进行模型构建，研究模块互作机制及各模块与L-乳酸合成效率的关联规律，对L-乳酸合成强化机制进行全局认识和系统性评价。研究成果将为高效生物合成L-乳酸奠定理论和技术基础。

This project plans to reveal the promotion mechanism of magnesium oxide in L-lactic acid biosynthesis using a multi-level study including the intracellular exploration, the extracellular characterization and the systematic intensification. Firstly, to reveal the influence of excess magnesium ions in gene transcription for L-lactic acid biosynthesis, a transcriptome analysis of Lactobacillus rhamnosus LA-04-1 under the stress of high magnesium ion concentration will be conducted, the transcription information will be further associated with the efficiency of L-lactic acid biosynthesis, and the target sites of excess magnesium ions will be identified. Secondly, to interprete the promotion effect of magnesium ion in bacteria metabolism, the flux analysis of the metabolic network model of L. rhamnosus LA-04-1 will be conducted based on the metabolomics, the relationship of substance and energy metabolism to L-lactic acid biosynthesis will be clarified, and the metabolic nodes significantly affected by excess magnesium ions will be located. In addition, to confirm the improvement effect, which provided by the fermentation microenvironment of recycled magnesium oxide, on L-lactic acid biosynthesis, the mechanisms (including interactions) of steric hindrance effect, distribution effect and diffusion effect among bacteria cells, substrates, product and the microenvironment will be studied, and the special composition of the recycled magnesium oxide will be investigated. Finally, in order to comprehensively reveal and systematically evaluate the enhancement mechanism of L-lactic acid biosynthesis, the building of kinetic and thermodynamic models will be conducted based on the intensification of the coupling system, and the interaction mechanisms of modules and the relationship between each module and L-lactic acid production efficiency will also be studied. Results obtained from this project will provide theoretical and technical basis for the efficient biosynthesis of L-lactic acid.