Addressing Fatty Acids Toxicity and Production in Biocatalysts.

摘要

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.;In current study, the toxicity of short chain fatty acids: hexanoic, octanoic, and decanoic acid on Saccharomyces. cerevisiae and Escherichia.coliwere 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 integrity, which was confirmed by increased membrane leakage. This induction of membrane leakage could be significantly decreased by introducing 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 integrity also occurred under octanoic acid stress. Futhermore, increased saturated:unsaturated lipid ratio in E. coli was also reported. Thus, manipulating membrane lipid to restore membrane integrity possibly overcome toxicity of fatty acids and improve production.;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 beta-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.