Engineering Kluyveromyces marxianus as a Robust Synthetic Biology Platform Host

Throughout history, the yeast has played a central role in human society due to its use in food production and more recently as a major industrial and model microorganism, because of the many genetic and genomic tools available to probe its biology. However, has proven difficult to engineer to expand the carbon sources it can utilize, the products it can make, and the harsh conditions it can tolerate in industrial applications. Other yeasts that could solve many of these problems remain difficult to manipulate genetically. Here, we engineered the thermotolerant yeast to create a new synthetic biology platform. Using CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats with Cas9)-mediated genome editing, we show that wild isolates of can be made heterothallic for sexual crossing. By breeding two of these mating-type engineered strains, we combined three complex traits-thermotolerance, lipid production, and facile transformation with exogenous DNA-into a single host. The ability to cross strains with relative ease, together with CRISPR-Cas9 genome editing, should enable engineering of isolates with promising lipid production at temperatures far exceeding those of other fungi under development for industrial applications. These results establish as a synthetic biology platform comparable to , with naturally more robust traits that hold potential for the industrial production of renewable chemicals. The yeast grows at high temperatures and on a wide range of carbon sources, making it a promising host for industrial biotechnology to produce renewable chemicals from plant biomass feedstocks. However, major genetic engineering limitations have kept this yeast from replacing the commonly used yeast in industrial applications. Here, we describe genetic tools for genome editing and breeding strains, which we use to create a new thermotolerant strain with promising fatty acid production. These results open the door to using as a versatile synthetic biology platform organism for industrial applications.