1-Ethyl-3-methylimidazolium tolerance and intracellular lipid accumulation of 38 oleaginous yeast species
Pretreatment with ionic liquids (IL) such as 1-ethyl-3-methylimidazolium chloride or acetate is an effective method for aiding deconstruction of lignocellulosic biomass; however, the residual IL remaining in hydrolysates can be inhibitory to growth of ethanologenic or oleaginous yeasts that have been examined in the literature. The aim of this study was to identify oleaginous yeasts that are tolerant of the IL [C2C1Im][OAc] and [C2C1Im]Cl using 45 strains belonging to 38 taxonomically diverse species within phyla Ascomycota and Basidiomycota. Yeasts were cultivated in laboratory medium supplemented with 0, 2, or 4% IL in 96-well plates. The eight most tolerant strains were then cultivated in 10-mL media with no IL, 242mM [C2C1Im][OAc], or 242mM [C2C1Im]Cl. The effects of [C2C1Im]+ exposure on cell mass production and lipid accumulation varied at the species and strain level. The acetate salt decreased cell biomass and lipid production more severely than did the chloride ion for six strains. Lipid output was not markedly different (2.1 vs. 2.3 g/L) in Yarrowia lipolytica UCDFST 51-30, but decreased from 5 to 65% in other yeasts. An equimolar concentration of the chloride salt resulted in much milder effects, from 25% decrease to 66% increase in lipid output. The highest lipid outputs in this media were 8.3 and 7.9 g/L produced by Vanrija humicola UCDFST 10-1004 and UCDFST 12-717, respectively. These results demonstrated substantial lipid production in the presence of [C2C1Im]Cl at concentrations found in lignocellulosic hydrolysates, and thus, these two strains are ideal candidates for further investigation.
KeywordsTriacylgylcerols Biodiesel 1-Ethyl-3-methylimidazolium acetate Pretreatment Lignocellulosic biofuels Oleaginous yeast
The authors thank Shuang Shi, Florencia Chua, Idelia Chandra, Erin Cathcart, Jennifer Lincoln, and Vania Rahardjo of the Department of Food Science and Technology, UC, Davis, for the technical assistance. The authors are grateful to the anonymous reviewers, whose comments and suggestions greatly improved the manuscript.
This project was supported by the United States Department of Agriculture (USDA) Agricultural Food Research Initiative of the National Food and Agriculture, USDA, Grant No. 35621-04750. This work was partially supported by the Science Translation and Innovation Research (STAIR) Grant Program of the University of California, Davis. The portion of the work carried out at the DOE Joint BioEnergy Institute (http://www.jbei.org) was supported by the U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research, through contract DE-AC02-05CH11231 between Lawrence Berkeley National Laboratory and the U. S. Department of Energy.
Compliance with ethical standards
Some yeasts used in this study were isolated and identified as part of a collaborative project with Indonesian Institute of Sciences (LIPI); Research, Development and Innovation Agency, the Ministry of Environment and Forestry; and the Government of the Republic of Indonesia, funded by Grant Number U01TW008160 from the National Institute of Health (NIH) Fogarty International Center (FIC), the NIH Office of Dietary Supplements, the National Science Foundation (NSF), and the Department of Energy (DOE). The content is solely the responsibility of the authors and does not necessarily represent the official views of the FIC or the NIH, the Office of Dietary Supplements, the NSF, the DOE, or the USDA. The authors declare that they have no conflict of interest. This article does not contain any studies with human participants or animals performed by any of the authors.
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