Synthesis of polyketides from low cost substrates by the thermotolerant yeast Kluyveromyces marxianus.

Kluyveromyces marxianus is a promising nonconventional yeast for biobased chemical production due to its rapid growth rate, high TCA cycle flux, and tolerance to low pH and high temperature. Unlike Saccharomyces cerevisiae, K. marxianus grows on low-cost substrates to cell densities that equal or surpass densities in glucose, which can be beneficial for utilization of lignocellulosic biomass (xylose), biofuel production waste (glycerol), and whey (lactose). We have evaluated K. marxianus for the synthesis of polyketides, using triacetic acid lactone (TAL) as the product. The 2-pyrone synthase (2-PS) was expressed on a CEN/ARS plasmid in three different strains, and the effects of temperature, carbon source, and cultivation strategy on TAL levels were determined. The highest titer was obtained in defined 1% xylose medium at 37 degrees C, with substantial titers at 41 and 43 degrees C. The introduction of a high-stability 2-PS mutant and a promoter substitution increased titer four-fold. 2-PS expression from a multi-copy pKD1-based plasmid improved TAL titers a further five-fold. Combining the best plasmid, promoter, and strain resulted in a TAL titer of 1.24 g/L and a yield of 0.0295 mol TAL/mol carbon for this otherwise unengineered strain in 3 ml tube culture. This is an excellent titer and yield (on xylose) before metabolic engineering or fed-batch culture relative to other hosts (on glucose), and demonstrates the promise of this rapidly growing and thermotolerant yeast species for polyketide production.