Ameliorating the Metabolic Burden of the Co-expression of Secreted Fungal Cellulases in a High Lipid-Accumulating Yarrowia lipolytica Strain by Medium C/N Ratio and a Chemical Chaperone

Journal Article · 09 January 2019 · Frontiers in Microbiology

DOI: https://doi.org/10.3389/fmicb.2018.03276 · OSTI ID:1490107

Wei, Hui  ^[1]; Wang, Wei ^[1]; Alper, Hal S. ^[2]; Xu, Qi ^[1]; Knoshaug, Eric P.  ^[1]; Van Wychen, Stefanie ^[1]; Lin, Chien -Yuan ^[1]; Luo, Yonghua ^[1]; Decker, Stephen R.  ^[1]; Himmel, Michael E. ^[1]; Zhang, Min ^[1]

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1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
2. The Univ. of Texas at Austin, Austin, TX (United States)

Yarrowia lipolytica, known to accumulate lipids intracellularly, lacks the cellulolytic enzymes needed to break down solid biomass directly. This study aimed to evaluate the potential metabolic burden of expressing core cellulolytic enzymes in an engineered high lipid-accumulating strain of Y. lipolytica. Three fungal cellulases, Talaromyces emersonii-Trichoderma reesei chimeric cellobiohydrolase I (chimeric-CBH I), T. reesei cellobiohydrolase II (CBH II), and T. reesei endoglucanase II (EG II) were expressed using three constitutive strong promoters as a single integrative expression block in a recently engineered lipid hyper-accumulating strain of Y. lipolytica (HA1). In yeast extract-peptone-dextrose (YPD) medium, the resulting cellulase co-expressing transformant YL165-1 had the chimeric-CBH I, CBH II, and EG II secretion titers being 26, 17, and 132 mg L^-1, respectively. Cellulase co-expression in YL165-1 in culture media with a moderate C/N ratio of ~4.5 unexpectedly resulted in a nearly two-fold reduction in cellular lipid accumulation compared to the parental control strain, a sign of cellular metabolic drain. Such metabolic drain was ameliorated when grown in media with a high C/N ratio of 59 having a higher glucose utilization rate that led to approximately twofold more cell mass and threefold more lipid production per liter culture compared to parental control strain, suggesting cross-talk between cellulase and lipid production, both of which involve the endoplasmic reticulum (ER). Most importantly, we found that the chemical chaperone, trimethylamine N-oxide dihydride increased glucose utilization, cell mass and total lipid titer in the transformants, suggesting further amelioration of the metabolic drain. In conclusion, this is the first study examining lipid production in cellulase-expressing Y. lipolytica strains under various C/N ratio media and with a chemical chaperone highlighting the metabolic complexity for developing robust, cellulolytic and lipogenic yeast strains.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Bioenergy Technologies Office (BETO)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1490107
• Alternate ID(s): OSTI ID: 1491724
• Report Number(s): NREL/JA-2700-73065
• Journal Information: Frontiers in Microbiology, Vol. 9; ISSN 1664-302X
• Publisher: Frontiers Research FoundationCopyright Statement
• Country of Publication: United States
• Language: English