A CRISPR/Cas9 method facilitates efficient oligo-mediated gene editing in Debaryomyces hansenii

Halophilic and osmotolerant yeast Debaryomyces hansenii has a high potential for cell factory applications due to its resistance to harsh environmental factors and compatibility with a wide substrate range. However, currently available genetic techniques do not allow the full potential of D. hansenii as a cell factory to be harnessed. Moreover, most of the currently available tools rely on the use of auxotrophic markers that are not suitable in wild-type prototrophic strains. In addition, the preferred non-homologous end-joining (NHEJ) DNA damage repair mechanism poses further challenges when precise gene targeting is required. In this study, we present a novel plasmid-based CRISPR^CUG/Cas9 method for easy and efficient gene editing of the prototrophic strains of D. hansenii. Our toolset design is based on a dominant marker and facilitates quick assembly of the vectors expressing Cas9 and single or multiple single-guide RNAs (sgRNAs) that provide the possibility for multiplex gene engineering even in prototrophic strains. Moreover, we have constructed NHEJ-deficient D. hansenii that enable our CRISPR^CUG/Cas9 tools to support the highly efficient introduction of point mutations and single/double gene deletions. Importantly, we also demonstrate that 90-nt single-stranded DNA oligonucleotides are sufficient for direct repair of DNA breaks induced by sgRNA-Cas9, resulting in precise edits reaching 100% efficiencies. In conclusion, tools developed in this study will greatly advance basic and applied research in D. hansenii. In addition, we envision that our tools can be rapidly adapted for gene editing of other non-conventional yeast species including the ones belonging to the CUG clade.