title: Mechanistic insights into the effect of imidazolium ionic liquid on lipid production byGeotrichum fermentans.
abstract: BACKGROUND
  Ionic liquid (IL) pretreatment has emerged as a promising technique that enables complete utilization of lignocellulosic biomass for biofuel production. However, imidazolium IL has recently been shown to exhibit inhibitory effect on cell growth and product formation of industrial microbes, such as oleaginous microorganisms. To date, the mechanism of this inhibition remains largely unknown.
  
  
  RESULTS
  In this study, the feasibility of [Bmim][OAc]-pretreated rice straw hydrolysate as a substrate for microbial lipid production byGeotrichum fermentans, also known asTrichosporon fermentans, was evaluated. The residual [Bmim][OAc] present in the hydrolysate caused a reduction in biomass and lipid content (43.6 and 28.1%, respectively) ofG. fermentans, compared with those of the control (7.8 g/L and 52.6%, respectively). Seven imidazolium ILs, [Emim][DEP], [Emim]Cl, [Amim]Cl, [Bmim]Cl, [Bzmim]Cl, [Emim][OAc], and [Bmim][OAc], capable of efficient pretreatment of lignocellulosic biomass were tested for their effects on the cell growth and lipid accumulation ofG. fermentansto better understand the impact of imidazolium IL on the lipid production. All the ILs tested inhibited the cell growth and lipid accumulation. In addition, both the cation and the anion of IL contributed to IL toxicity. The side chain of IL cations showed a clear impact on toxicity. On examining IL anions, [OAc]-was found to be more toxic than those of [DEP]-and Cl-. IL exhibited its toxicity by inhibiting sugar consumption and key enzyme (malic enzyme and ATP-citrate lyase) activities ofG. fermentans. Cell membrane permeability was also altered to different extents in the presence of various ILs. Scanning electron microscopy revealed that IL induces fibrous structure on the surface ofG. fermentanscell, which might represent an adaptive mechanism of the yeast to IL.
  
  
  CONCLUSIONS
  This work gives some mechanistic insights into the impact of imidazolium IL on the cell growth and lipid accumulation of oleaginous yeast, which is important for IL integration in lignocellulosic biofuel production, especially for microbial lipid production.
authors.affiliation: School of Bioscience and Bioengineering, South China University of Technology, Guangzhou Higher Education Mega Centre, 382 East Waihuan Rd., Panyu District, Guangzhou, 510006 China.
authors.forename: Li-Ping
authors.initials: LP
authors.lastname: Liu
authors.affiliation: School of Food Science and Engineering, South China University of Technology, Room 409, Building 13, 381 Wushan Rd., Tianhe District, Guangzhou, 510640 China.
authors.forename: Min-Hua
authors.initials: MH
authors.lastname: Zong
authors.affiliation: Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York, 12180 USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Linhardt
authors.affiliation: School of Food Science and Engineering, South China University of Technology, Room 409, Building 13, 381 Wushan Rd., Tianhe District, Guangzhou, 510640 China.
authors.forename: Wen-Yong
authors.initials: WY
authors.lastname: Lou
authors.affiliation: School of Food Science and Engineering, South China University of Technology, Room 409, Building 13, 381 Wushan Rd., Tianhe District, Guangzhou, 510640 China.
authors.forename: Ning
authors.initials: N
authors.lastname: Li
authors.affiliation: Key Laboratory of Renewable Energy, Chinese Academy of Sciences, 2 Nengyuan Rd., Tianhe District, Guangzhou, 510640 China.
authors.forename: Chao
authors.initials: C
authors.lastname: Huang
authors.affiliation: School of Food Science and Engineering, South China University of Technology, Room 409, Building 13, 381 Wushan Rd., Tianhe District, Guangzhou, 510640 China ; Guangdong Province Key Laboratory for Green Processing of Natural Products and Product Safety, 381 Wushan Rd., Tianhe District, Guangzhou, 510640 China.
authors.forename: Hong
authors.initials: H
authors.lastname: Wu
keywords: Geotrichum fermentans; Imidazolium ionic liquid; Inhibition; Lignocellulosic hydrolysate; Lipid production