title: Furfural tolerance and detoxification mechanism inCandida tropicalis.
abstract: BACKGROUND
  Current biomass pretreatment by hydrothermal treatment (including acid hydrolysis, steam explosion, and high-temperature steaming) and ionic liquids generally generate inhibitors to the following fermentation process. Furfural is one of the typical inhibitors generated in hydrothermal treatment of biomass. Furfural could inhibit cell growth rate and decrease biofuel productivity of microbes.Candida tropicalisis a promising microbe for the production of biofuels and value-added chemicals using hemicellulose hydrolysate as carbon source. In this study,C. tropicalisshowed a comparable ability of furfural tolerance during fermentation. We investigated the mechanism ofC. tropicalis's robust tolerance to furfural and relevant metabolic responses to obtain more information for metabolic engineering of microbes for efficient lignocellulose fermentation.
  
  
  RESULTS
  Candida tropicalisshowed comparable intrinsic tolerance to furfural and a fast rate of furfural detoxification.C. tropicalis's half maximal inhibitory concentration for furfural with xylose as the sole carbon source was 3.69 g/L, which was higher than that of most wild-type microbes reported in the literature to our knowledge. Even though furfural prolonged the lag phase ofC. tropicalis, the final biomass in the groups treated with 1 g/L furfural was slightly greater than that in the control groups. By real-time PCR analysis, we found that the expression ofADH1inC. tropicalis(ctADH1) was induced by furfural and repressed by ethanol after furfural depletion. The expression ofctADH1could be regulated by both furfural and ethanol. After the disruption of genectADH1, we found thatC. tropicalis's furfural tolerance was weakened. To further confirm the function ofctADH1and enhanceEscherichia coli's furfural tolerance,ctADH1was overexpressed inE. coliBL21 (DE3). The rate of furfural degradation inE. coliBL21 (DE3) with pET-ADH1 (high-copy plasmid) and pCS-ADH1 (medium-copy plasmid) was increased by 1.59-fold and 1.28-fold, respectively.
  
  
  CONCLUSIONS
  Candida tropicaliswas a robust strain with intrinsic tolerance to inhibitor furfural. The mechanism of furfural detoxification and metabolic responses were identified by multiple analyses. Alcohol dehydrogenase 1 was confirmed to be responsible for furfural detoxification.C. tropicalisshowed a complex regulation system during furfural detoxification to minimize adverse effects caused by furfural. Furthermore, the mechanism we uncovered in this work was successfully applied to enhanceE. coli's furfural tolerance by heterologous expression ofctADH1. The study provides deeper insights into strain modification for biofuel production by efficient lignocellulose fermentation.
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Shizeng
authors.initials: S
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Gang
authors.initials: G
authors.lastname: Cheng
authors.affiliation: Deconstruction Division, Joint BioEnergy Institute, Emeryville, CA 94608 USA.
authors.forename: Chijioke
authors.initials: C
authors.lastname: Joshua
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Zijun
authors.initials: Z
authors.lastname: He
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Xinxiao
authors.initials: X
authors.lastname: Sun
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Ruimin
authors.initials: R
authors.lastname: Li
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Lexuan
authors.initials: L
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, West Room 314, Science and Technology Building, No. 15 North Third Ring East Road, Chaoyang District, Beijing, 100029 People's Republic of China.
authors.forename: Qipeng
authors.initials: Q
authors.lastname: Yuan
keywords: Alcohol dehydrogenase 1; Candida tropicalis; Furfural detoxification; Furfural tolerance