title: Optimization of fatty alcohol biosynthesis pathway for selectively enhanced production of C12/14 and C16/18 fatty alcohols in engineered Escherichia coli.
abstract: BACKGROUND
  With the increasing stress from oil price and environmental pollution, aroused attention has been paid to the microbial production of chemicals from renewable sources. The C12/14 and C16/18 alcohols are important feedstocks for the production of surfactants and detergents, which are widely used in the most respected consumer detergents, cleaning products and personal care products worldwide. Though bioproduction of fatty alcohols has been carried out in engineered E. coli, several key problems have not been solved in earlier studies, such as the quite low production of C16/18 alcohol, the lack of optimization of the fatty alcohol biosynthesis pathway, and the uncharacterized performance of the engineered strains in scaled-up system.
  
  
  RESULTS
  We improved the fatty alcohol production by systematically optimizing the fatty alcohol biosynthesis pathway, mainly targeting three key steps from fatty acyl-acyl carrier proteins (ACPs) to fatty alcohols, which are sequentially catalyzed by thioesterase, acyl-coenzyme A (CoA) synthase and fatty acyl-CoA reductase. By coexpression of thioesterase gene BTE, acyl-CoA synthase gene fadD and fatty acyl-CoA reductase gene acr1, 210.1 mg/L C12/14 alcohol was obtained. A further optimization of expression level of BTE, fadD and acr1 increased the C12/14 alcohol production to 449.2 mg/L, accounting for 75.0% of the total fatty alcohol production (598.6 mg/L). In addition, by coexpression of thioesterase gene 'tesA, acyl-CoA synthase gene fadD and fatty acyl-CoA reductase gene FAR, 101.5 mg/L C16/18 alcohol was obtained, with C16/18 alcohol accounting for 89.2% of the total fatty alcohol production.
  
  
  CONCLUSIONS
  To our knowledge, this is the first report on selective production of C12/14 and C16/18 alcohols by microbial fermentation. This work achieved high-specificity production of both C12/14 and C16/18 alcohols. The encouraging 598.6 mg/L of fatty alcohols represents the highest titer reported so far. In addition, the 101.5 mg/L 89.2% C16/18 alcohol suggests an important breakthrough in C16/18 alcohol production. A more detailed optimization of the expression level of fatty alcohol biosynthesis pathway may contribute to a further improvement of fatty alcohol production.
authors.affiliation: Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Laoshan District, Qingdao 266101, China.
authors.forename: Yan-Ning
authors.initials: YN
authors.lastname: Zheng
authors.forename: Ling-Ling
authors.initials: LL
authors.lastname: Li
authors.forename: Qiang
authors.initials: Q
authors.lastname: Liu
authors.forename: Jian-Ming
authors.initials: JM
authors.lastname: Yang
authors.forename: Xiang-Wei
authors.initials: XW
authors.lastname: Wang
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Xin
authors.initials: X
authors.lastname: Xu
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.forename: Guang
authors.initials: G
authors.lastname: Zhao
authors.forename: Mo
authors.initials: M
authors.lastname: Xian
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways; D003066:Coenzyme A Ligases / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005233:Fatty Alcohols / Q000737:chemistry / Q000378:metabolism*; D005285:Fermentation; D005818:Genetic Engineering; D007218:Industrial Microbiology; D015394:Molecular Structure; D015854:Up-Regulation
chemical_list: D029968:Escherichia coli Proteins; D005233:Fatty Alcohols; D000445:Aldehyde Oxidoreductases; C021351:hexadecanal dehydrogenase (acylating); D003066:Coenzyme A Ligases