A survey of yeast from the Yarrowia clade for lipid production in dilute-acid pretreated lignocellulosic biomass hydrolysate

Authors: Quarterman, Joshua; Slininger, Patricia - Pat; Kurtzman, Cletus; Thompson, Stephanie; Dien, Bruce

Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2016
Publication Date: 4/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5754225
Citation: Quarterman, J., Slininger, P.J., Kurtzman, C.P., Thompson, S.R., Dien, B.S. 2017. A survey of yeast from the Yarrowia clade for lipid production in dilute-acid pretreated lignocellulosic biomass hydrolysate. Applied Microbiology and Biotechnology. 101(8):3319-3334. doi: 10.1007/s00253-016-8062-y.

Interpretive Summary: Yarrowia lipolytica (Y. lipolytica) is an industrial yeast used for production of numerous fermentation products including lipids, organic acids, and enzymes. It has also become popular for metabolic engineering of recombinant products with biofuel and chemical applications. One potential application of Y. lipolytica is its use for conversion of sugars derived from agricultural biomass, such as corn stover or perennial grasses grown as dedicated biomass crops. Switchgrass, which is used in this study, is an ARS flagship crop being specifically developed for biomass production on marginal farmlands. However, growth on sugars prepared from such biomass is challenging for industrial microorganisms because of toxic chemicals generated during processing to sugars. In this paper, 57 yeast strains deposited in the ARS Culture Collection were challenged for their ability to grow on a hydrolysate prepared from the dedicated biomass crop switchgrass. Our hypothesis was that the strains would vary in their robustness for growth on the hydrolysate, and some would prove to be hardier than the few previously examined for commercial fermentations. In fact, several Y. lipolytica strains were discovered with exceptional hardiness as borne by their ability to grow on up to 90% strength switchgrass hydrolysate. These yeasts are ideal hosts for future metabolic engineering projects where the final application is the conversion of biomass to value-added fermentation products. This work will be of interest to lipid yeast researchers or to fermentation and agricultural processing-related companies seeking to develop new products using yeast.

Technical Abstract: Yarrowia lipolytica is an oleaginous yeast species that has attracted attention as a model organism for synthesis of single cell oil. Among over 50 isolates of Y. lipolytica identified, only a few of the strains have been studied extensively. Furthermore, 12 other yeast species were recently assigned to the Yarrowia clade, and most are not well-characterized in terms of cell growth and lipid accumulation, especially in industrially relevant conditions. In the present study, we investigated biomass and lipid production by 57 yeast isolates, representing all 13 species in the Yarrowia clade, on a non-detoxified dilute acid-pretreated switchgrass hydrolysate under highly aerobic conditions. The objective was to compare yeast physiology during growth in an abundant, low-cost biomass feedstock, and to expand diversity of genetically-tractable, oleaginous yeasts available for lipid research. Screening of 45 Y. lipolytica isolates demonstrated considerable variation within the species in terms of lipid accumulation (min=0.1 g/L; max=5.1 g/L; mean=2.3 g/L); three strains (NRRL YB-420, YB-419, and YB-392) were especially promising for cellulosic biomass conversion with average improvements of 43%, 57%, and 64%, respectively, in final lipid titer as compared to control strain W29. Subsequently, evaluation of strains from 13 distinct species in the Yarrowia clade identified Candida phangngensis PT1-17 as the top lipid producer with a maximum titer of 9.8 g/L lipid, which was over two-fold higher than the second-best species in the clade (Candida hollandica NRRL Y-48254). A small set of the most promising strains from the screenings was further characterized to evaluate inhibitor tolerance, lipid production kinetics, and fatty acid distribution. We expect that the results of this study will pave the way for new biotechnological applications involving previously overlooked and under-characterized strains within the Yarrowia clade.