Ionic Liquid Tolerance of Yeasts in Family Dipodascaceae and Genus Wickerhamomyces Irnayuli Sitepu 1 & Lauren Enriquez 1 & Valerie Nguyen 1 & Russell Fry 1 & Blake Simmons 2,3 & Steve Singer 2,4 & Christopher Simmons 1 & Kyria L. Boundy-Mills 1 Received: 18 December 2019 /Accepted: 13 February 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract In previous studies of ionic liquid (IL) tolerance of numerous species of ascomy- cetous yeasts, two strains of Wickerhamomyces ciferrii and Galactomyces candidus had unusually high tolerance in media containing up to 5% (w/v) of the 1-ethyl-3- methylimidazolium acetate ([C 2 C 1 Im][OAc]). The study aimed at investigating whether additional strains of these species, and additional species in the Dipodascaceae family, also possess IL tolerance, and to compare sensitivity to the acetate and chloride versions of the ionic liquid. Fifty five yeast strains in the family Dipodascaceae, which encompasses genera Galactomyces, Geotrichum, and Dipodascus, and seven yeast strains of species Wickerhamomyces ciferrii were tested for ability to grow in laboratory medium containing no IL, 242 mM [C 2 C 1 Im][OAc], or 242 mM [C 2 C 1 Im]Cl, and in IL-pretreated switchgrass hydro- lysate. Many yeasts exhibited tolerance of one or both ILs, with higher tolerance of the chloride anion than of the acetate anion. Different strains of the same species exhibited varying degrees of IL tolerance. Galactomyces candidus, UCDFSTs 52– 260, and 50–64, had exceptionally robust growth in [C 2 C 1 Im][OAc], and also grew well in the switchgrass hydrolysate. Identification of IL tolerant and IL resistant yeast strains will facilitate studies of the mechanism of IL tolerance, which could include superior efflux, metabolism or exclusion. Keywords Ionic liquid pretreatment . Lignocellulosic biofuels . Inhibitor tolerance . Switchgrass hydrolysate . Tolerant yeast . Galactomyces candidus https://doi.org/10.1007/s12010-020-03293-y Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12010-020- 03293-y] contains supplementary material, which is available to authorized users. * Kyria L. Boundy-Mills klbmills@ucdavis.edu Extended author information available on the last page of the article Published online: 17 March 2020 Applied Biochemistry and Biotechnology (2020) 191:1580–1593