Transcriptome analysis of parallel-evolved Escherichia coli strains under ethanol stress.
BACKGROUND
Understanding ethanol tolerance in microorganisms is important for the improvement of bioethanol production. Hence, we performed parallel-evolution experiments using Escherichia coli cells under ethanol stress to determine the phenotypic changes necessary for ethanol tolerance.


RESULTS
After cultivation of 1,000 generations under 5% ethanol stress, we obtained 6 ethanol-tolerant strains that showed an approximately 2-fold increase in their specific growth rate in comparison with their ancestor. Expression analysis using microarrays revealed that common expression changes occurred during the adaptive evolution to the ethanol stress environment. Biosynthetic pathways of amino acids, including tryptophan, histidine, and branched-chain amino acids, were commonly up-regulated in the tolerant strains, suggesting that activating these pathways is involved in the development of ethanol tolerance. In support of this hypothesis, supplementation of isoleucine, tryptophan, and histidine to the culture medium increased the specific growth rate under ethanol stress. Furthermore, genes related to iron ion metabolism were commonly up-regulated in the tolerant strains, which suggests the change in intracellular redox state during adaptive evolution.


CONCLUSIONS
The common phenotypic changes in the ethanol-tolerant strains we identified could provide a fundamental basis for designing ethanol-tolerant strains for industrial purposes.
Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, Japan.
Takaaki
T
Horinouchi
Kuniyasu
K
Tamaoka
Chikara
C
Furusawa
Naoaki
N
Ono
Shingo
S
Suzuki
Takashi
T
Hirasawa
Tetsuya
T
Yomo
Hiroshi
H
Shimizu
D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D000596:Amino Acids / Q000494:pharmacology; D019020:Directed Molecular Evolution; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D000431:Ethanol / Q000633:toxicity*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005798:Genes, Bacterial / Q000235:genetics; D007477:Ions; D007501:Iron / Q000494:pharmacology; D025341:Principal Component Analysis; D018085:Regulon / Q000235:genetics; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics*
D000596:Amino Acids; D007477:Ions; D000431:Ethanol; D007501:Iron