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J Ind Microbiol Biotechnol (2010) 37:12111220 DOI 10.1007/s10295-010-0768-8
ORIGINAL PAPER
Adaptation of the xylose fermenting yeast Saccharomyces cerevisiae F12 for improving ethanol productionin different fed-batch SSF processes
E. Toms-Pej M. Ballesteros J. M. Oliva
L. Olsson
Received: 5 April 2010 / Accepted: 14 June 2010 / Published online: 29 June 2010 Society for Industrial Microbiology 2010
Abstract An efcient fermenting microorganism for bioethanol production from lignocellulose is highly tolerant to the inhibitors released during pretreatment and is able to ferment efciently both glucose and xylose. In this study, directed evolution was employed to improve the xylose fermenting Saccharomyces cerevisiae F12 strain for bioethanol production at high substrate loading. Adapted and parental strains were compared with respect to xylose consumption and ethanol production. Adaptation led to an evolved strain more tolerant to the toxic compounds present in the medium. When using concentrated prehydroly-sate from steam-pretreated wheat straw with high inhibitor concentration, an improvement of 65 and 20% in xylose consumption and nal ethanol concentration, respectively, were achieved using the adapted strain. To address the need of high substrate loadings, fed-batch SSF experiments were performed and an ethanol concentration as high as27.4 g/l (61% of the theoretical) was obtained with 11.25% (w/w) of water insoluble solids (WIS).
Keywords Bioethanol Xylose
Evolutionary engineering Fed-batch S. cerevisiae
Introduction
The depletion of the world petroleum supply as well as increased levels of greenhouse gases have recently stimulated extensive interest in optimizing fermentation processes for large-scale production of alternative biofuels such as bioethanol [1]. In this context, bioethanol produced from lignocellulose, the so-called second-generation bioethanol, is an interesting alternative. Lignocellulosic bio-mass such as agricultural residues, forest products or energy crops do not compete with food crops, and in addition, these side-streams from food production are also less expensive than conventional agricultural feedstocks [2].
Owing to the structural characteristics of the lignocellulosic materials, pretreatment is a crucial step for obtaining potentially fermentable sugars in the hydrolysis step. Steam explosion is one of the more widely exploited pretreatments. It offers several attractive features when compared to other pretreatment technologies, including the potential for signicantly lower environmental impact, lower capital investment, larger potential for energy efciency, less hazardous chemicals and conditions and complete sugar recovery [3]. During steam explosion pretreatment, ber structure is altered...