title: Enhancing E. coli isobutanol tolerance through engineering its global transcription factor cAMP receptor protein (CRP).
abstract: The limited isobutanol tolerance of Escherichia coli is a major drawback during fermentative isobutanol production. Different from classical strain engineering approaches, this work was initiated to improve E. coli isobutanol tolerance from its transcriptional level by engineering its global transcription factor cAMP receptor protein (CRP). Random mutagenesis libraries were generated by error-prone PCR of crp, and the libraries were subjected to isobutanol stress for selection. Variant IB2 (S179P, H199R) was isolated and exhibited much better growth (0.18 h(-1) ) than the control (0.05 h(-1) ) in 1.2% (v/v) isobutanol (9.6 g/L). Genome-wide DNA microarray analysis revealed that 58 and 308 genes in IB2 had differential expression (>2-fold, p < 0.05) in the absence and presence of 1% (v/v) isobutanol, respectively. When challenged with isobutanol, genes related to acid resistance (gadABCE, hdeABD), nitrate reduction (narUZYWV), flagella and fimbrial activity (lfhA, yehB, ycgR, fimCDF), and sulfate reduction and transportation (cysIJH, cysC, cysN) were the major functional groups that were up-regulated, whereas most of the down-regulated genes were enzyme (tnaA) and transporters (proVWX, manXYZ). As demonstrated by single-gene knockout experiments, gadX, nirB, rhaS, hdeB, and ybaS were found associated with strain isobutanol resistance. The intracellular reactive oxygen species (ROS) level in IB2 was only half of that of the control when facing stress, indicating that IB2 can withstand toxic isobutanol much better than the control.
authors.affiliation: School of Chemical & Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore, 637459, Singapore.
authors.forename: Huiqing
authors.initials: H
authors.lastname: Chong
authors.forename: Hefang
authors.initials: H
authors.lastname: Geng
authors.forename: Hongfang
authors.initials: H
authors.lastname: Zhang
authors.forename: Hao
authors.initials: H
authors.lastname: Song
authors.forename: Lei
authors.initials: L
authors.lastname: Huang
authors.forename: Rongrong
authors.initials: R
authors.lastname: Jiang
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000440:Butanols / Q000378:metabolism*; D002373:Cyclic AMP Receptor Protein / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D055786:Gene Knockout Techniques; D060847:Metabolic Engineering / Q000379:methods*
chemical_list: D000440:Butanols; D002373:Cyclic AMP Receptor Protein; C040507:isobutyl alcohol
keywords: biofuel; cAMP receptor protein; global regulator; isobutanol tolerance; strain engineering; transcriptional engineering