Fluorescent proteins are ubiquitous tools that are used to monitor the dynamic functions of natural and synthetic genetic circuits. However, these visual reporters can only be used in transparent settings, a limitation that complicates nondisruptive measurements of gene expression within many matrices, such as soils and sediments. We describe a new ratiometric gas reporting method for nondisruptively monitoring gene expression within hard-to-image environmental matrices. With this approach, C₂H₄ is continuously synthesized by ethylene forming enzyme to provide information on viable cell number, and CH₃Br is conditionally synthesized by placing a methyl halide transferase gene under the control of a conditional promoter. We show that ratiometric gas reporting enables the creation of Escherichia coli biosensors that report on acylhomoserine lactone (AHL) autoinducers used for quorum sensing by Gram-negative bacteria. Using these biosensors, we find that an agricultural soil decreases the bioavailable concentration of a long-chain AHL up to 100-fold. We also demonstrate that these biosensors can be used in soil to nondisruptively monitor AHLs synthesized by Rhizobium leguminosarum and degraded by Bacillus thuringiensis. Finally, we show that this new reporting approach can be used in Shewanella oneidensis, a bacterium that lives in sediments.

中文翻译：

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比例气体报告：一种监测土壤中基因表达的非破坏性方法

荧光蛋白是无处不在的工具，用于监测天然和合成遗传电路的动态功能。但是，这些视觉报告器只能在透明的环境中使用，这一局限性使得无中断测量基因在许多基质（例如土壤和沉积物）中的表达变得复杂。我们描述了一种新的比例气体报告方法，用于无中断监视难以成像的环境矩阵中的基因表达。通过这种方法，C ₂ H ₄由乙烯形成酶连续合成以提供有关活细胞数的信息，而CH ₃通过将甲基卤化物转移酶基因置于条件启动子的控制下，有条件地合成Br。我们显示比例气体报告使创建大肠杆菌生物传感器的报告用于酰基革兰氏阴性菌群体感应的酰基高丝氨酸内酯（AHL）自动诱导剂。使用这些生物传感器，我们发现农业土壤将长链AHL的生物利用浓度降低了多达100倍。我们还证明了这些生物传感器可以在土壤中用于无干扰地监测豆科根瘤菌合成和苏云金芽孢杆菌降解的AHLs 。最后，我们证明了这种新的报告方法可以在沙瓦氏菌中使用，一种生活在沉积物中的细菌。