Design of a Genetically Encoded Biosensor for High-Throughput Screening and Engineering 5-Aminolevulinic Acid Hyper-Producing Escherichia coli

5-Aminolevulinic acid (ALA) is a multifunctional nonprotein amino acid used in agriculture, medicine, and other fields. As current environmental problems become increasingly serious, it is of great significance to establish a cheap, environmentally friendly, and sustainable way to synthesize ALA. Therefore, the biosynthesis of ALA is receiving increasing attention. However, the lack of high-throughput screening methods for ALA has become a limiting factor in improving microbial production of ALA. In this study, a high-throughput screening method was developed based on the relationship between reactive oxygen species (ROS) caused by ALA and cyclic adenosine monophosphate (cAMP). First, the relationship between the ROS accumulation and changes in cAMP levels was verified. Subsequently, the selected promoter was optimized by adding cAMP receptor protein (CRP) binding sites at its upstream, and a high-throughput screening method for ALA was established. HemA mutant and ALA-producing Escherichia coli strain mutant were obtained and combined with a series of metabolic engineering strategies to improve ALA production. Finally, the ALA fed-batch fermentation in a 5 L fermenter achieved the highest ALA titer of 58.54 g/L with a productivity of 1.58 g/L/h. This laid the foundation for the industrialization of ALA through biosynthesis.