title: Exploiting Issatchenkia orientalis SD108 for succinic acid production.
abstract: BACKGROUND
  Recent advances in synthesizing valuable chemicals such as organic acids from low-cost renewable biomass through microbial fermentation have attracted great attention. However, 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 organic acids but also tolerates the associated toxicity is highly desirable.
  
  
  RESULTS
  Here we report the discovery, characterization, and engineering of a yeast strain, Issatchenkia orientalis SD108, that is tolerant to low pH and high concentration of organic acids. This strain demonstrated a higher tolerance compared to I. orientalis ATCC 24210 and Classic Distiller's Turbo yeast. In order to explore SD108 as a potential platform organism for organic acid production, we determined its draft genome sequence and use the sequencing information to guide pathway design. As proof of concept, an engineered four-gene expression cassette related to the reductive TCA cycle was assembled and integrated into the genome of a uracil auxotroph of SD108. The resulting strain was able to produce succinic acid with a titer of 11.63 g/L, yield of 0.12 g/g, and productivity of 0.11 g/L · h in batch cultures using shake flasks.
  
  
  CONCLUSIONS
  The high tolerance of I. orientalis SD108 towards multiple important organic acids makes it a highly attractive organism as a platform host for producing this group of compounds as it will reduce production cost, facilitate downstream processing, and serve as a host for construction of production strains with both pH and specific anion tolerance.
authors.forename: Han
authors.initials: H
authors.lastname: Xiao
authors.forename: Zengyi
authors.initials: Z
authors.lastname: Shao
authors.forename: Yu
authors.initials: Y
authors.lastname: Jiang
authors.forename: Sudhanshu
authors.initials: S
authors.lastname: Dole
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana 61801, IL, USA. zhao5@illinois.edu.
authors.forename: Huimin
authors.initials: H
authors.lastname: Zhao
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D061249:Batch Cell Culture Techniques; D050260:Carbohydrate Metabolism / Q000187:drug effects; D005285:Fermentation / Q000187:drug effects; D016681:Genome, Fungal / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D060847:Metabolic Engineering; D055442:Metabolome / Q000187:drug effects; D011003:Ploidies; D017422:Sequence Analysis, DNA; D019802:Succinic Acid / Q000378:metabolism* / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014498:Uracil / Q000378:metabolism; D015003:Yeasts / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D014498:Uracil; D019802:Succinic Acid