Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/20/2004
Publication Date: 8/15/2004
Citation: Gorsich, S.W., Dien, B.S., Nichols, N.N., Slininger, P.J., Liu, Z. 2004. The Saccharomyces cerevisiae pentose phosphate pathway gene, rpe1, functions in furfural tolerance during fermentation [abstract]. Proceedings of the 11th International Congress on Yeasts in Science and Biotechnology. Paper No. PM24.
Technical Abstract: Lignocellulosic biomass is potentially a low-cost substrate for fermentative production of ethanol. However, to release sugars (glucose, xylose, and arabinose) from lignocellulose an acid hydrolysis procedure is often utilized. Unfortunately, growth inhibitors, furfural and 5-hydroxymethylfurfural (HMF) are also generated as degradation products of xylose and glucose, respectively. Furfural and HMF competitively inhibit alcohol dehydrogenase and aldehyde dehydrogenase. This results in an accumulation of the cellular toxin, acetaldehyde, and decreases ethanol yield. Engineering yeast to be more tolerant of these inhibitors is expected to increase ethanol yields and make bioconversion of lignocellulose to ethanol more cost effective. However, at the genetic level, little is known about how these inhibitors affect cellular physiology. In this study, a Saccharomyces cerevisiae disruption library was screened to identify genes that function in furfural tolerance or metabolism. The screen identified 29 genes that, when disrupted, cause a growth defect in the presence of 25 mM furfural. Of these disruptions, rpe1 was of particular interest. RPE1 encodes D-ribulose 5-phosphate 3-epimerase, which functions in the non-oxidative portion of the pentose phosphate pathway in yeast. Recently, RPE1 and other pentose phosphate genes have been shown to have an important function in genetically engineered xylose-fermenting S. cerevisiae strains. In the present study, rpe1 disruption cells did not grow in 25 mM furfural and had a 65-hour lag before growth in 15 mM furfural. Wild-type cells had a lag time of 12 to 18 hours in 25 mM furfural and less than 12 hours in 15 mM furfural. Neither rpe1 disruption cells nor wild-type cells were inhibited in 5 mM furfural. HPLC analysis suggests that one possible mechanism responsible for growth inhibition is the inability of cells lacking Rpelp to completely metabolize furfural into furfuryl alcohol. Interestingly, rpe1 disruption cells did not have a comparable growth defect in the presence of HMF or ethanol. Moreover, other gene mutants in the pentose phosphate pathway (tal1, ygr043c, tkl1, tkl2, gnd1, gnd2, and zwf1) did not have the same furfural induced growth defect seen in the rpe1 disruption.