Fig. 1.

Schematic diagram of the generation and utilization of auxotrophic markers for engineering yeast. Random mutagenesis of host DNA or homologous recombination of a cassette that inactivates an essential gene for nutrient synthesis can be used to produce stable auxotrophic strains. The presence of an auxotrophy allows more advanced genome editing and pathway engineering tools to be applied in the yeast species of interest. Shown here are 1) targeted and random integration using a selectable marker (bottom, left), 2) HisG/lacZ-mediated marker recovery (bottom, middle), 3) Cre-lox-mediated marker recovery (bottom, middle), and 4) Markerless editing by CRISPR-Cas9 (bottom, right).