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The damaging effects of short chain fatty acids on Escherichia coli membranes.

ABSTRACT: Carboxylic acids are an attractive biorenewable chemical. However, like many other fermentatively produced compounds, they are inhibitory to the biocatalyst. An understanding of the mechanism of toxicity can aid in mitigating this problem. Here, we show that hexanoic and octanoic acids are completely inhibitory to Escherichia coli MG1655 in minimal medium at a concentration of 40 mM, while decanoic acid was inhibitory at 20 mM. This growth inhibition is pH-dependent and is accompanied by a significant change in the fluorescence polarization (fluidity) and integrity. This inhibition and sensitivity to membrane fluidization, but not to damage of membrane integrity, can be at least partially mitigated during short-term adaptation to octanoic acid. This short-term adaptation was accompanied by a change in membrane lipid composition and a decrease in cell surface hydrophobicity. Specifically, the saturated/unsaturated lipid ratio decreased and the average lipid length increased. A fatty acid-producing strain exhibited an increase in membrane leakage as the product titer increased, but no change in membrane fluidity. These results highlight the importance of the cell membrane as a target for future metabolic engineering efforts for enabling resistance and tolerance of desirable biorenewable compounds, such as carboxylic acids. Knowledge of these effects can help in the engineering of robust biocatalysts for biorenewable chemicals production.

SUBMITTER: Royce LA

PROVIDER: S-EPMC3757260 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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The damaging effects of short chain fatty acids on Escherichia coli membranes.

Royce Liam A LA Liu Ping P Stebbins Matthew J MJ Hanson Benjamin C BC Jarboe Laura R LR

Applied microbiology and biotechnology 20130803 18

Carboxylic acids are an attractive biorenewable chemical. However, like many other fermentatively produced compounds, they are inhibitory to the biocatalyst. An understanding of the mechanism of toxicity can aid in mitigating this problem. Here, we show that hexanoic and octanoic acids are completely inhibitory to Escherichia coli MG1655 in minimal medium at a concentration of 40 mM, while decanoic acid was inhibitory at 20 mM. This growth inhibition is pH-dependent and is accompanied by a signi ...[more]

PMID: 23912117

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Project description:BackgroundRecent progress in production of various biofuel precursors and molecules, such as fatty acids, alcohols and alka(e)nes, is a significant step forward for replacing the fossil fuels with renewable fuels. A two-step process, where fatty acids from sugars are produced in the first step and then converted to corresponding biofuel molecules in the second step, seems more viable and attractive at this stage. We have engineered an Escherichia coli strain to take care of the second step for converting short chain fatty acids into corresponding alcohols by using butyrate kinase (Buk), phosphotransbutyrylase (Ptb) and aldehyde/alcohol dehydrogenase (AdhE2) from Clostridium acetobutylicum.ResultsThe engineered E. coli was able to convert butyric acid and other short chain fatty acids of chain length C3 to C7 into corresponding alcohols and the efficiency of conversion varied with different E. coli strain type. Glycerol proved to be a better donor of ATP and electron as compared to glucose for converting butyric acid to butanol. The engineered E. coli was able to tolerate up to 100 mM butyric acid and produced butanol with the conversion rate close to 100% under anaerobic condition. Deletion of native genes, such as fumarate reductase (frdA) and alcohol dehydrogenase (adhE), responsible for side products succinate and ethanol, which act as electron sink and could compete with butyric acid uptake, did not improve the butanol production efficiency. Indigenous acyl-CoA synthetase (fadD) was found to play no role in the conversion of butyric acid to butanol. Engineered E. coli was cultivated in a bioreactor under controlled condition where 60 mM butanol was produced within 24 h of cultivation. A continuous bioreactor with the provision of cell recycling allowed the continuous production of butanol at the average productivity of 7.6 mmol/l/h until 240 h.ConclusionsE. coli engineered with the pathway from C. acetobutylicum could efficiently convert butyric acid to butanol. Other short chain fatty acids with the chain length of C3 to C7 were also converted to the corresponding alcohols. The ability of engineered strain to convert butyric acid to butanol continuously demonstrates commercial significance of the system.

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The damaging effects of short chain fatty acids on Escherichia coli membranes.

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The damaging effects of short chain fatty acids on Escherichia coli membranes.

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