Membrane stress caused by octanoic acid in Saccharomyces cerevisiae

Abstract

In order to compete with petroleum-based fuel and chemicals, engineering a robust biocatalyst that can convert renewable feedstocks into biorenewable chemicals, such as carboxylic acids, is increasingly important. However, product toxicity is often problematic. In this study, the toxicity of the carboxylic acids hexanoic, octanoic, and decanoic acid on Saccharomyces cerevisiae was investigated, with a focus on octanoic acid. These compounds are completely inhibitory at concentrations of magnitude 1 mM, and the toxicity increases as chain length increases and as media pH decreases. Transciptome analysis, reconstruction of gene regulatory network, and network component analysis suggested decreased membrane integrity during challenge with octanoic acid. This was confirmed by quantification of dose-dependent and chain length-dependent induction of membrane leakage, though membrane fluidity was not affected. This induction of membrane leakage could be significantly decreased by a period of pre-adaptation, and this preadaptation was accompanied by increased oleic acid content in the membrane, significantly increased production of saturated lipids relative to unsaturated lipids, and a significant increase in the average lipid chain length in the membrane. However, during adaptation cell surface hydrophobicity was not altered. The supplementation of oleic acid to the medium not only elevated the tolerance of yeast cells to octanoic acid but also attenuated the membrane leakiness. However, while attempts to mimic the oleic acid supplementation effects through expression of the Trichoplusia ni acyl-CoA Δ9 desaturase OLE1(TniNPVE desaturase) were able to increase the oleic acid content, the magnitude of the increase was not sufficient to reproduce the supplementation effect and increase octanoic acid tolerance. Similarly, introduction of cyclopropanated fatty acids through expression of the Escherichia coli cfa gene was not helpful for tolerance. Thus, we have provided quantitative evidence that carboxylic acids damage the yeast membrane and that manipulation of the lipid content of the membrane can increase tolerance, and possibly production, of these valuable products.

Med15B Regulates Acid Stress Response and Tolerance in Candida glabrata by Altering Membrane Lipid Composition

“…Our genome-wide analyses confirmed the critical role played by the composition and structure of the membrane lipid and its physiological function in acid tolerance (46)(47)(48). Deletion of MED15B decreased the long-chain fatty acid and phospholipid proportion and the UFA/SFA ratio and blocked the biosynthesis of fecosterol and ergosterol, thereby increasing the zymosterol concentration to 2,866.1 g/g cells (dry weight) at pH 2.0.…”

Engineering fungal de novo fatty acid synthesis for short chain fatty acid production

“…Regarding a putative impact on growth by toxic SCFAs3637, we were interested in clarifying whether a strong initial production of C 8 -FA accounts for the inhibition of further growth. Product spectra of selected strains were recorded after 12, 24 and 48 h; the latter constituting the regularly chosen measurement point.…”

Crz1p Regulates pH Homeostasis in Candida glabrata by Altering Membrane Lipid Composition

“…To maintain pH homeostasis and cope with acidic conditions, microorganisms have developed a number of strategies. These include manipulating the lengths and saturation of fatty acid chains (43,44,49), the contents and types of sterols (48), and the presence of specific phospholipids, such as phosphatidic acid (45), cardiolipin (47), and some inositol phosphates (46). Changes in lipid composition of the Cgcrz1⌬ mutant might affect the activity of membrane proteins essential for barrier function (50,51).…”