title: Direct ethanol production from cellulosic materials at high temperature using the thermotolerant yeast Kluyveromyces marxianus displaying cellulolytic enzymes.
abstract: To exploit cellulosic materials for fuel ethanol production, a microorganism capable of high temperature and simultaneous saccharification-fermentation has been required. However, a major drawback is the optimum temperature for the saccharification and fermentation. Most ethanol-fermenting microbes have an optimum temperature for ethanol fermentation ranging between 28 degrees C and 37 degrees C, while the activity of cellulolytic enzymes is highest at around 50 degrees C and significantly decreases with a decrease in temperature. Therefore, in the present study, a thermotolerant yeast, Kluyveromyces marxianus, which has high growth and fermentation at elevated temperatures, was used as a producer of ethanol from cellulose. The strain was genetically engineered to display Trichoderma reesei endoglucanase and Aspergillus aculeatus beta-glucosidase on the cell surface, which successfully converts a cellulosic beta-glucan to ethanol directly at 48 degrees C with a yield of 4.24 g/l from 10 g/l within 12 h. The yield (in grams of ethanol produced per gram of beta-glucan consumed) was 0.47 g/g, which corresponds to 92.2% of the theoretical yield. This indicates that high-temperature cellulose fermentation to ethanol can be efficiently accomplished using a recombinant K. marxianus strain displaying thermostable cellulolytic enzymes on the cell surface.
authors.affiliation: Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodaicho, Nada, Kobe, 657-8501, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Yanase
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Hasunuma
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Yamada
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Tanaka
authors.forename: Chiaki
authors.initials: C
authors.lastname: Ogino
authors.forename: Hideki
authors.initials: H
authors.lastname: Fukuda
authors.forename: Akihiko
authors.initials: A
authors.lastname: Kondo
mesh_terms: D001230:Aspergillus / Q000201:enzymology / Q000235:genetics; D002475:Cellobiose / Q000378:metabolism; D044602:Cellulases / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006358:Hot Temperature; D007716:Kluyveromyces / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D014242:Trichoderma / Q000201:enzymology / Q000235:genetics
chemical_list: D005656:Fungal Proteins; D011994:Recombinant Proteins; D002475:Cellobiose; D000431:Ethanol; D002482:Cellulose; D044602:Cellulases; D005947:Glucose