(41h) Exploiting Issatchenkia Orientalis SD108 As a New Platform Organism for Organic Acids Production

The toxicity of organic acids presents a key challenge to the development of an economically viable fermentation process.  Therefore, a platform organism that not only produces a high level of organic acids but also tolerates the associated toxicity is highly desirable.  Issatchenkia orientalis strain SD108 was found to be tolerant to low pH and high concentration of organic acids.  It can ferment fructose as efficiently as glucose, while no growth on other sugars (xylose, arabinose, cellobiose, galactose and sucrose) was observed.  Tolerance assays were subsequently carried out with acetic acid, succinic acid, itaconic acid, and adipic acid.  SD108 could grow even when the concentrations of succinic acid and adipic acid approached or exceeded their aqueous solubility limits and demonstrated a superior tolerance towards all four of these organic acids compared to I. orientalis ATCC 24210 and Classic Distiller’s Turbo yeast.  The draft genome sequence of SD108 was provided, which offers a basis for our future functional genomics studies on its tolerance mechanisms and a source for engineering individual organic acid biosynthetic pathways.  As proof of concept, metabolic engineering strategies were further applied in SD108 for succinic acid production.  By exploiting genome information, four gene expression cassettes related to the reductive TCA cycle were assembled and integrated into the genome of uracil auxotroph of SD108.  The final engineered strain was able to reach a titer of 11.63 g/L, yield of 0.12 g/g, and productivity of 0.11 g/L·h of succinic acid.