(599cd) Engineering a Yeast Platform Strain for Industrial Production of Polyketides

Polyketides are a diverse and important class of naturally-derived compounds with applications in pharmaceuticals, nutrition, and flavouring. Industrial production of important polyketides or their precursors in yeast has the potential to significantly lower manufacturing costs on existing products, as well as open up new products for commercialization. Intensive efforts in enzyme discovery and yeast synthetic biology have already enabled heterologous production of a handful of nonnative polyketides in yeast, but yields and titres are currently too low for commercial feasibility, partly due to the high material and energy cost to the cells needed to build these compounds. Here, we describe recent efforts to engineer yeast metabolism to channel metabolic flux towards common polyketide precursors in order to develop "platform strains" that are optimized for hosting heterologous polyketide production pathways. In our approach, steady-state constraint-based computational models assisted in the design of knockouts in the pentose phosphate pathway that force overproduction of the aromatic amino acid precursor erythrose 4-phosphate (E4P), and kinetic models suggest modifications to reaction kinetics in glycolysis that promote higher steady state concentrations of phosphoenol pyruvate (PEP). We demonstrate the implementation of these modifications in the Saccharomyces cerevisiae strain CEN.PK and combine them with manipulations of feedback inhibition of aromatic amino acid biosynthesis and remedies to cofactor imbalances created by the knockouts in the pentose phosphate pathway. The impacts of these modifications are examined in the context of a heterologous pathway for the production of a model polyketide. Our results indicate that platform strain performance depends on balanced cofactor levels, availability of critical precursors, and regulation of synthetic pathway expression levels.