Inducible promoters of bacterial microcompartments improve the CRISPR/Cas9 tools for efficient metabolic engineering of <i>Clostridium ljungdahlii</i>

A CRISPR/Cas9 genetic tool controlled by a constitutive promoter has been developed for precise gene deletion in <i>Clostridium ljungdahlii</i>. However, its efficiency was hindered by the toxicity resulting from the constitutive expression of cas9 and the large plasmids, leading to a low overall success rate. Inducible promoters, which allow for the transcription of target genes to be switched on and off in the presence or absence of inducers, have a broad range of applications. In this study, we identify two inducible promoters and apply them to enhance the CRISPR/Cas9 tools. The improved CRISPR/Cas9 tools facilitate gene editing with high efficiency, potentially playing significant roles in advancing genetic research and metabolic engineering of <i>C. ljungdahlii</i>.