title: Improving Escherichia coli membrane integrity and fatty acid production by expression tuning of FadL and OmpF.
abstract: BACKGROUND
  Construction of microbial biocatalysts for the production of biorenewables at economically viable yields and titers is frequently hampered by product toxicity. Membrane damage is often deemed as the principal mechanism of this toxicity, particularly in regards to decreased membrane integrity. Previous studies have attempted to engineer the membrane with the goal of increasing membrane integrity. However, most of these works focused on engineering of phospholipids and efforts to identify membrane proteins that can be targeted to improve fatty acid production have been unsuccessful.
  
  
  RESULTS
  Here we show that deletion of outer membrane protein ompF significantly increased membrane integrity, fatty acid tolerance and fatty acid production, possibly due to prevention of re-entry of short chain fatty acids. In contrast, deletion of fadL resulted in significantly decreased membrane integrity and fatty acid production. Consistently, increased expression of fadL remarkably increased membrane integrity and fatty acid tolerance while also increasing the final fatty acid titer. This 34% increase in the final fatty acid titer was possibly due to increased membrane lipid biosynthesis. Tuning of fadL expression showed that there is a positive relationship between fadL abundance and fatty acid production. Combinatorial deletion of ompF and increased expression of fadL were found to have an additive role in increasing membrane integrity, and was associated with a 53% increase the fatty acid titer, to 2.3 g/L.
  
  
  CONCLUSIONS
  These results emphasize the importance of membrane proteins for maintaining membrane integrity and production of biorenewables, such as fatty acids, which expands the targets for membrane engineering.
authors.affiliation: 4134 Biorenewables Research Laboratory, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA.
authors.forename: Zaigao
authors.initials: Z
authors.lastname: Tan
authors.affiliation: 4134 Biorenewables Research Laboratory, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA.|Department of Chemical Engineering and Materials Sciences, University of California, 916 Engineering Tower Irvine, Irvine, CA, 92697-2575, USA.
authors.forename: William
authors.initials: W
authors.lastname: Black
authors.affiliation: 4134 Biorenewables Research Laboratory, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA.
authors.forename: Jong Moon
authors.initials: JM
authors.lastname: Yoon
authors.affiliation: 4134 Biorenewables Research Laboratory, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA.
authors.forename: Jacqueline V
authors.initials: JV
authors.lastname: Shanks
authors.affiliation: 4134 Biorenewables Research Laboratory, Department of Chemical and Biological Engineering, Iowa State University, Ames, IA, 50011, USA. ljarboe@iastate.edu.
authors.forename: Laura R
authors.initials: LR
authors.lastname: Jarboe
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics* / Q000502:physiology*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D050612:Fatty Acid Transport Proteins / Q000235:genetics* / Q000378:metabolism; D005227:Fatty Acids / Q000096:biosynthesis*; D017353:Gene Deletion; D015870:Gene Expression; D008563:Membrane Lipids / Q000096:biosynthesis; D018272:Porins / Q000235:genetics*; D017384:Sequence Deletion
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D050612:Fatty Acid Transport Proteins; D005227:Fatty Acids; D008563:Membrane Lipids; C109237:OmpF protein; D018272:Porins; C065691:fadL protein, E coli
keywords: Fatty acid production; Membrane engineering; Membrane integrity; Outer membrane protein; Tolerance