title: Impact of two ionic liquids, 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium methylphosphonate, on Saccharomyces cerevisiae: metabolic, physiologic, and morphological investigations.
abstract: BACKGROUND
  Ionic liquids (ILs) are considered as suitable candidates for lignocellulosic biomass pretreatment prior enzymatic saccharification and, obviously, for second-generation bioethanol production. However, several reports showed toxic or inhibitory effects of residual ILs on microorganisms, plants, and animal cells which could affect a subsequent enzymatic saccharification and fermentation process.
  
  
  RESULTS
  In this context, the impact of two hydrophilic imidazolium-based ILs already used in lignocellulosic biomass pretreatment was investigated: 1-ethyl-3-methylimidazolium acetate [Emim][OAc] and 1-ethyl-3-methylimidazolium methylphosphonate [Emim][MeO(H)PO2]. Their effects were assessed on the model yeast for ethanolic fermentation, Saccharomyces cerevisiae, grown in a culture medium containing glucose as carbon source and various IL concentrations. Classical fermentation parameters were followed: growth, glucose consumption and ethanol production, and two original factors: the respiratory status with the oxygen transfer rate (OTR) and carbon dioxide transfer rate (CTR) of yeasts which were monitored online by respiratory activity monitoring systems (RAMOS). In addition, yeast morphology was characterized by environmental scanning electron microscope (ESEM). The addition of ILs to the growth medium inhibited the OTR and switched the metabolism from respiration (conversion of glucose into biomass) to fermentation (conversion of glucose to ethanol). This behavior could be observed at low IL concentrations (≤5% IL) while above there is no significant growth or ethanol production. The presence of IL in the growth medium also induced changes of yeast morphology, which exhibited wrinkled, softened, and holed shapes. Both ILs showed the same effects, but [Emim][MeO(H)PO2] was more biocompatible than [Emim][OAc] and could be better tolerated by S. cerevisiae.
  
  
  CONCLUSIONS
  These two imidazolium-derived ILs were appropriate candidates for useful pretreatment of lignocellulosic biomass in the context of second-generation bioethanol production. This fundamental study provides additional information about the toxic effects of ILs. Indeed, the investigations highlighted the better tolerance by S. cerevisiae of [Emim][MeO(H)PO2] than [Emim][OAc].
authors: Unité Génie Enzymatique et Cellulaire, FRE-CNRS 3580, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France.
authors: Nasir
authors: N
authors: Mehmood
authors: Unité Génie Enzymatique et Cellulaire, FRE-CNRS 3580, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France.
authors: Eric
authors: E
authors: Husson
authors: Unité de Recherche Vignes et Vins de Champagne-UPRES-EA 4707, Université de Reims Champagne-Ardenne, BP1039, 51687 Reims Cedex 2, France.
authors: Cédric
authors: C
authors: Jacquard
authors: AVT-Biochemical Engineering, RWTH Aachen University, Aachen, Germany.
authors: Sandra
authors: S
authors: Wewetzer
authors: AVT-Biochemical Engineering, RWTH Aachen University, Aachen, Germany.
authors: Jochen
authors: J
authors: Büchs
authors: Unité Génie Enzymatique et Cellulaire, FRE-CNRS 3580, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France.
authors: Catherine
authors: C
authors: Sarazin
authors: Unité Génie Enzymatique et Cellulaire, FRE-CNRS 3580, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039 Amiens Cedex, France.
authors: Isabelle
authors: I
authors: Gosselin
keywords: Environmental scanning electronic microscopy; Ionic liquid; Respirofermentative metabolism; Saccharomyces cerevisiae; Second-generation bioethanol