A CRISPR-Cas12a system for multi-gene editing (CCMGE) and metabolic pathway assembly in Starmerella bombicola

The traditional homologous recombination (HR) gene-editing method faces problems such as low editing efficiency and absence of marker genes. CRISPR-Cas9-editing efficiency is high and has been widely used in bacteria and yeast. In comparison with CRISPR-Cas9, CRISPR-Cas12a has many outstanding advantages. Here, we report an Acidaminococcus sp. BV3L6 (As) Cas12a-based genome-editing method used for Starmerella bombicola. To demonstrate the high efficiency of the CCMGE system, we verified a counter-selectable marker in S. bombicola, orotidine 5'-phosphate decarboxylase (100% for URA3). We also tested the common gene UDP-glucosyltransferase (100% for UGTA) using a 300 bp donor containing hygromycin expression cassette. This toolkit was further extended to simultaneously edit two genes (18% for UGTA and leu) and three genes (13.8% for UGTA, leu and URA3). The system greatly reduces the screening time for such multi-site editing. Based on the CCMGE system, the PHA (polyhydroxyalkanoate)-producing strain was constructed by increasing the copy number of the PHA synthase (PHAC). The PHA content and DCW reached 11.8% and 30.1 g/L, respectively. The yield of PHA was about three times higher than that of the single-copy strain using the same fermentation method.