Yeast strains
Inventors
Slininger, Patricia J. • Thompson, Stephanie R. • Balan, Venkatesh • Da Costa Sousa, Leonardo • Dale, Bruce E. • Shea Andersh, Maureen A. • Dien, Bruce S.
Assignees
Michigan State University MSU • US Department of Agriculture USDA
Publication Number
US-9873896-B2
Publication Date
2018-01-23
Expiration Date
2034-01-29
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Abstract
Several mutated strains of Scheffersomyces stipitis are generated by repetitive culturing of the parent strain on two types of concentrated hydrolyzates and with ethanol-challenged xylose-fed continuous culture. Isolates collected from various enriched populations are screened and ranked based on relative xylose uptake rate and ethanol yield. Ranking on hydrolyzates with and without nutritional supplementation is used to identify those isolates with best performance across diverse conditions.
Core Innovation
This invention relates to novel strains of Scheffersomyces stipitis with enhanced capabilities to produce ethanol from diverse lignocellulosic hydrolyzates. The invention includes methods involving repetitive culturing of parent S. stipitis strains on different hydrolyzate media types and ethanol-challenged, xylose-fed continuous culture to select isolates with superior performance in terms of xylose uptake rate and ethanol yield. The medium types used in the culturing steps differ and include combinations of low furfural, low HMF, high acetic acid and high nitrogen concentration (e.g., AFEX-CSH), xylose-rich with low glucose (e.g., PSGHL), glucose and xylose-rich hydrolyzate (e.g., SGH), and media with high ethanol concentration along with high xylose. Optional irradiation by ultraviolet light prior to or during cultivation steps is also included as part of the method to induce mutations.
The background problem being addressed is the difficulty of converting lignocellulosic biomass to ethanol due to the recalcitrance of plant cell-wall material and the presence of toxic fermentation inhibitors such as acetic acid, furfural, and hydroxymethyl furfural in hydrolyzates. Traditional industrial yeasts do not ferment xylose efficiently and are poorly tolerant to toxic concentrated hydrolyzates with sugar concentrations sufficient for economical ethanol recovery. Although Scheffersomyces stipitis strain NRRL Y-7124 ferments xylose more efficiently than other native yeasts and can accumulate over 40 g/L ethanol in optimized media, it remains sensitive to fermentation inhibitors and exhibits issues such as diauxic lag during transition from glucose to xylose fermentation.
The invention addresses the need for S. stipitis strains with improved tolerance to diverse lignocellulosic hydrolyzates and inhibitors, enhanced xylose utilization leading to higher ethanol yield and productivity, reduced diauxic lag in presence of ethanol concentrations of approximately 15 to 20 g/L or more, and robustness across diverse nutritional environments. The methods developed enable the generation of novel and isolated S. stipitis strains that produce at least approximately 40 g/L ethanol from diverse hydrolyzates, including those derived from woody and herbaceous biomass sources, thereby supporting cost-effective ethanol production from lignocellulosic biomass.
Claims Coverage
The claims include two independent claims focusing on an isolated Scheffersomyces stipitis strain with enhanced fermentation properties and a method for producing ethanol using such strains. Two inventive features are identified.
Isolated Scheffersomyces stipitis strain with enhanced ethanol production and reduced lag phase
An isolated S. stipitis strain characterized by a shorter lag preceding growth phase when cultured on non-detoxified lignocellulosic hydrolyzate compared to the parent strain NRRL Y-7124. The strain produces at least 35 g/L ethanol under these conditions and is selected from strains bearing ARS patent deposit accession numbers NRRL Y-50857, Y-50858, Y-50860, Y-50863, Y-50865, Y-50872, Y-50873, and Y-50874.
Method of producing ethanol using the isolated S. stipitis strains
A method comprising growing at least one of the claimed isolated S. stipitis strains on lignocellulosic hydrolyzate for a time effective to allow the strain to grow and ferment the hydrolyzate to ethanol.
The claims cover both novel isolated S. stipitis strains with superior lag and ethanol production characteristics and methods employing these strains to produce ethanol from lignocellulosic hydrolyzates.
Stated Advantages
The novel S. stipitis strains produce higher ethanol titers (at least approximately 40 g/L) from diverse lignocellulosic hydrolyzates compared to the parent strain.
The strains exhibit reduced diauxic lag during the sugar transition from glucose to xylose, especially in the presence of ethanol concentrations of about 15 g/L or more.
The strains have improved tolerance to fermentation inhibitors including acetic acid, furfural, hydroxymethylfurfural, and ethanol.
The strains demonstrate more rapid initial growth, more rapid glucose and xylose uptake rates, and higher ethanol productivity under diverse nutrient environments.
Documented Applications
Producing ethanol from lignocellulosic biomass using the novel S. stipitis strains developed by the described adaptation methods.
Utilization of diverse, non-detoxified lignocellulosic hydrolyzates including ammonia fiber explosion-pretreated corn stover hydrolyzate (AFEX-CSH), dilute acid-pretreated switchgrass hydrolyzate liquor (PSGHL), and switchgrass hydrolyzate (SGH) with or without nutrient supplementation.
Ethanol production processes where improved fermentation performance is needed in the presence of fermentation inhibitors and high sugar concentrations.
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