Developing an endogenous quorum-sensing based CRISPRi circuit for autonomous and tunable dynamic regulation of multiple targets in industrial Streptomyces

Dynamic regulation has emerged as an effective strategy to improve product titers by balancing metabolic networks, which can be implemented by coupling gene expression to pathway-independent regulatory elements, such as quorum-sensing (QS) systems. However, these QS-based circuits are often created on heterologous systems and must be carefully tuned through tedious testing and optimization process to make them work well, which hampers their application in industrial microbes including streptomycetes. In this study, we design a pathway-independent QS circuit by directly integrating an endogenous QS system with CRISPRi (named EQCi) in the industrial rapamycin-producing strain Streptomyces rapamycinicus. EQCi has the advantages of both the QS system and CRISPRi, which enables tunable, fully autonomous and dynamic regulation of multiple targets simultaneously. To demonstrate its effectiveness, we downregulate three key nodes in essential pathways separately to divert metabolic flux toward rapamycin biosynthesis. In each case, significant increases in rapamycin titers are achieved. We further apply EQCi to simultaneously control these three key nodes with proper repression strength by changing sgRNA targeting positions. The final rapamycin titer reaches to 1836{+/-}191 mg/L, which is the highest reported titer. Notably, compared to traditional static engineering strategy, which result in growth arrest and suboptimal rapamycin titers, EQCi regulation substantially promote rapamycin titers without affecting cell growth, which indicates that it can achieve the trade-off between essential pathways and product synthesis. Collectively, this study provides a simple and effective strategy for optimizing product titers and may have the potential to apply to other industrial microorganisms.