Addressing Fatty Acids Toxicity and Production in Biocatalysts

Abstract

<p>Fatty acids recently gain more attentions due to its potentials as fuel and chemicals. However, they are toxic to biocatalysts like many other biofuel compounds. Understanding the inhibitory mechanism can help to improve the production of fatty acids.</p> <p>In current study, the toxicity of short chain fatty acids: hexanoic, octanoic, and decanoic acid on Saccharomyces. cerevisiae and Escherichia.coli were inverstigated with a focus on octanoic acid. The toxicity of fatty acids (hexanoic, octanoic, and decanoic acid) in S. cerevisiae is dependent on doses and chain lengths, and also leads to damaged membrane intergirity, which was confirmed by increased membreane leakage. This induction of membrane leakage could be significantly decreased by inctroducing endogenous oleic acid into cell membrane. Although E.coli cells showed different response from S. cerevisiae when stressed by hexanoic, octanoic, and decanoic acid, similar disrupted membrane intergirity also occurred under octanoic acid stress. Futhermore, increased saturated:unsaturated lipid ratio in E. coli was also reported. Thus, manipulating memberane lipid to restore membrane integrity possibly overcome toxicity of fatty acids and improve production.</p> <p>Medium chain length carboxylic acids drive more attention because of their broad application in our life. In this thesis, Transcriptomic analysis was applied to construct a robust E.coli strain for production of medium chain length fatty acids. The first generation engineered strain ML103 (pXZ18Z) (deletion of fatty acid β-oxidation pathway, over-expression of fatty acid elongation gene (fabZ) and acyl-ACP thioesterase from R. communis ) was used as a host strain to study the possible pathway. Transcriptome analysis revealed a series of disturbed genes and transcription factors including stress response, biofilm, transporters, nitrogen limitation and membrane disruption.</p>