Microorganisms play a vital role in shaping the soil environment and enhancing plant growth by interacting with plant root systems. Due to the vast diversity of cell types involved, combined with dynamic and spatial heterogeneity, identifying the causal contribution of a defined factor, such as a microbial exopolysaccharide (EPS), remains elusive. Synthetic approaches that enable orthogonal control of microbial pathways are a promising means to dissect such complexity. Here we report the implementation of a synthetic, light-activated, transcriptional control platform in the nitrogen fixing soil bacterium Sinorhizobium meliloti. By fine tuning the system, we successfully achieved optical control of an EPS production pathway without significant basal expression under non-inducing (dark) conditions. Optical control of EPS recapitulated important behaviors such as a mucoid plate phenotype and formation of structured biofilms, enabling spatial control of biofilm structures in S. meliloti. The successful implementation of optically controlled gene expression in S. meliloti enables systematic investigation of how genotype and microenvironmental factors together shape phenotype in situ.

中文翻译：

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苜蓿中华根瘤菌的光遗传学使空间控制外多糖的产生和生物膜结构成为可能

微生物通过与植物根系相互作用，在塑造土壤环境和促进植物生长方面发挥着至关重要的作用。由于涉及的细胞类型的多样性，以及动态和空间异质性，确定可定义因素（如微生物胞外多糖（EPS））的因果贡献仍然难以捉摸。能够正交控制微生物途径的合成方法是剖析这种复杂性的有前途的手段。在这里，我们报告固氮土壤细菌苜蓿中华根瘤菌中合成，光激活，转录控制平台的实施。通过对系统进行微调，我们成功地实现了EPS生产途径的光学控制，而在非诱导（黑暗）条件下却没有明显的基础表达。EPS的光学控制概括了重要的行为，例如粘液板表型和结构化生物膜的形成，从而可以对苜蓿链球菌中的生物膜结构进行空间控制。S. meliloti中的光学控制基因表达的成功实施使系统地研究基因型和微环境因子如何一起原位形成表型。