title: Impact of pseudo-continuous fermentation on the ethanol tolerance of Scheffersomyces stipitis.
abstract: In this work we conducted the pseudo-continuous fermentation, i.e., continuous fermentation with cell retention, using Scheffersomyces stipitis, and studied its effect on ethanol tolerance of the strain. During the fermentation experiments, S. stipitis was adapted to a mild concentration of ethanol (20-26 g/L) for two weeks. Two substrates (glucose and xylose) were used in different fermentation experiments. After fermentation, various experiments were performed to evaluate the ethanol tolerance of adapted cells and unadapted cells. Compared to the unadapted cells, the viability of adapted cells increased by 8 folds with glucose as the carbon source and 6 folds with xylose as the carbon source following exposure to 60 g/L ethanol for 2 h. Improved ethanol tolerance of the adapted cells was also revealed in the effects of ethanol on plasma membrane permeability, extracellular alkalization and acidification. The mathematical modeling of cell leakage, extracellular alkalization and acidification revealed that cells cultured on glucose show better ethanol tolerance than cells cultured on xylose but the differences become smaller for adapted cells. The results show that pseudo-continuous fermentation can effectively improve cell's ethanol tolerance due to the environmental pressure during the fermentation process.
authors.affiliation: Department of Chemical Engineering, Auburn University, Auburn, AL 36849, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Liang
authors.forename: Min Hea
authors.initials: MH
authors.lastname: Kim
authors.forename: Qinghua Peter
authors.initials: QP
authors.lastname: He
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D000431:Ethanol / Q000378:metabolism / Q000494:pharmacology*; D005110:Extracellular Space / Q000737:chemistry; D005285:Fermentation / Q000187:drug effects; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008027:Light; D050296:Microbial Viability / Q000187:drug effects; D004718:Saccharomycetales / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D014994:Xylose / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000431:Ethanol; D014994:Xylose; D005947:Glucose
keywords: Adaptation; Cellulosic ethanol; Ethanol fermentation; Ethanol tolerance; Scheffersomyces stipitis