Enhancement of Free Fatty Acids Production in Rhodotorula toruloides Using the CRISPR/Cas9-Based Base Editor

Rhodotorula toruloides is a promising cell factory to produce various value-added chemicals, including fatty acid derivatives. However, their metabolic engineering development has been hindered by the limited availability of genetic tools. In this study, an accurate and specific gene-editing tool, CRISPR/Cas-based cytidine base editor (CBE) system, was developed for the first time in R. toruloides to broaden its genetic toolbox. The target gene was disrupted by introducing a premature stop codon via C to T mutation. This system achieved single-gene disruption efficiencies of up to 90% and successfully disrupted four genes in parallel with 5% efficiency, marking a breakthrough in multiplexed editing for this yeast. To enable iterative engineering, an inducible Cre-loxP system was integrated, achieving an over 70% selection marker recycling efficiency. Application of this system enabled the construction of uracil-auxotrophic strains. Furthermore, the CBE system was employed to disrupt four genes involved in lipid metabolism, resulting in an engineered strain capable of producing 512.3 mg/L of free fatty acids, thereby demonstrating the utility of the CBE system as an efficient genome editing tool in R. toruloides. The study provides valuable tools to expand the genetic toolbox of R. toruloides and paves the way for fully exploiting its metabolic engineering potential.