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Evolution for exogenous octanoic acid tolerance improves carboxylic acid production and membrane integrity

Paper ID Volume ID Publish Year Pages File Format Full-Text
31524 44807 2015 9 PDF Available
Title
Evolution for exogenous octanoic acid tolerance improves carboxylic acid production and membrane integrity
Abstract

•Evolution for octanoic acid tolerance increased fatty acid production 5-fold.•Evolution for octanoic acid tolerance extended to other fatty acids and butanol.•The evolved strain had altered membrane fluidity and integrity.•The evolved strain had significantly longer membrane lipids.

Carboxylic acids are an attractive biorenewable chemical, but as with many biorenewables, their toxicity to microbial biocatalysts limits their fermentative production. While it is generally accepted that membrane damage is the main mechanism of fatty acid toxicity, previous metabolic engineering efforts that increased membrane integrity did not enable increased carboxylic acid production. Here we used an evolutionary approach to improve tolerance to exogenous octanoic acid, with the goal of learning design strategies from this evolved strain. This evolution of an Escherichia coli MG1655 derivative at neutral pH in minimal media produced a strain with increased tolerance not only to octanoic acid, but also to hexanoic acid, decanoic acid, n-butanol and isobutanol. This evolved strain also produced carboxylic acids at a 5-fold higher titer than its parent strain when expressing the Anaerococcus tetradius thioesterase. While it has been previously suggested that intracellular acidification may contribute to carboxylic acid toxicity, we saw no evidence that the evolved strain has increased resistance to this acidification. Characterization of the evolved strain membrane showed that it had significantly altered membrane polarization (fluidity), integrity (leakage) and composition relative to its parent. The changes in membrane composition included a significant increase in average lipid length in a variety of growth conditions, including 30 °C, 42 °C, carboxylic acid challenge and ethanol challenge. The evolved strain has a more dynamic membrane composition, showing both a larger number of significant changes and larger fold changes in the relative abundance of membrane lipids. These results highlight the importance of the cell membrane in increasing microbial tolerance and production of biorenewable fuels and chemicals.

Keywords
Fatty acids; Membrane fluidity; Membrane composition; Membrane integrity; Membrane leakage; Intracellular acidification
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Evolution for exogenous octanoic acid tolerance improves carboxylic acid production and membrane integrity
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Publisher
Database: Elsevier - ScienceDirect
Journal: Metabolic Engineering - Volume 29, May 2015, Pages 180–188
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us