Shifting the distribution: modulation of the lipid profile in Yarrowia lipolytica via iron content.

Microbial fermentation offers a sustainable source of fuels, commodity chemicals, and pharmaceuticals, yet strain performance is influenced greatly by the growth media selected. Specifically, trace metals (e.g., iron, copper, manganese, zinc, and others) are critical for proper growth and enzymatic function within microorganisms yet are non-standardized across media formulation. In this work, the effect of trace metal supplementation on the lipid production profile of Yarrowia lipolytica was explored using tube scale fermentation followed by biomass and lipid characterization. Addition of iron (II) to the chemically defined Yeast Synthetic Complete (YSC) medium increased final optical density nearly twofold and lipid production threefold, while addition of copper (II) had no impact. Additionally, dose-responsive changes in lipid distribution were observed, with the percent of oleic acid increasing and stearic acid decreasing as initial iron concentration increased. These changes were reversible with subsequent iron-selective chelation. Use of rich Yeast Peptone Dextrose (YPD) medium enabled further increases in the production of two specialty oleochemicals ultimately reaching 63 and 47% of the lipid pool as α-linolenic acid and cyclopropane fatty acid, respectively, compared to YSC medium. Selective removal of iron (II) natively present in YPD medium decreased this oleochemical production, ultimately aligning the lipid profile with that of non-supplemented YSC medium. These results provide further insight into the proposed mechanisms for iron regulation in yeasts especially as these productions strains contain a mutant allele of the iron regulator, mga2. The work presented here also suggests a non-genetic method for control of the lipid profile in Y. lipolytica for use in diverse applications. KEY POINTS: • Iron supplementation increases cell density and lipid titer in Yarrowia lipolytica. • Iron addition reversibly alters lipid portfolio increasing linolenic acid. • Removal of iron from YPD media provides a link to enhanced oleochemical production.

Expanding the Chemical Palette of Industrial Microbes: Metabolic Engineering for Type III PKS-Derived Polyketides.

Polyketides are a unique class of molecules with attractive bioactive and chemical properties. As a result, biorenewable production is being explored with these molecules as potential pharmaceutical, fuel, and material precursors. In particular, type III polyketide synthases enable access to a diverse class of chemicals using a relatively simple biochemical synthesis pathway. In this review, the recent advances in the engineering of microbial hosts for the production of type III PKS-derived polyketides are highlighted. In particular, the field has moved beyond simple proof-of-concept and has been exploring engineering efforts that have led to improved production scales. This review details engineering progress for the production of acetyl-CoA- and malonyl-CoA-derived polyketides including the products triacetic acid lactone and phloroglucinol as well as polyphenolic, phenylpropanoid-derived compounds including flavonoids, stilbenoids, and curcuminoids. Specifically, the authors focus on enumerating the metabolic engineering strategies employed and product titers achieved for these molecules. Finally, the authors highlight tools and strategies that can be leveraged to realize the potential of microbial production and diversification of these molecules.