(421be) 13C –Based Metabolic Flux Analysis of Saccharomyces Cerevisiae Under Octanoic Acid Inhibition

Short-chained fatty acids synthesized via fermentation from biorenewable feedstocks are a potential source of platform chemicals, and thus could help replace the traditional petrochemical’s dependence on crude oil. However, toxicity of fatty acids is an obstacle in the high titer of fatty acid production and it remains a key challenge in metabolic engineering. Metabolic flux analysis (MFA), the quantification of fluxes in metabolic pathways, is an integral tool for the development of strategies for genetic modification and the identification of metabolic regulation, by comparing fluxes under different environments. We used Saccharomyces cerevisiae as a model system  to study the effect of toxicity of octanoic acid. The exposure of octanoic acid to yeast caused significant growth inhibition. We elucidated the metabolic flux differences in central metabolism between control and octanoic acid inhibition by conducting ¹³C labeling experiments using fermentors.  The yeast cultures were fed with a mixture of uniformly ¹³C labeled glucose and 1-¹³C positional labeled glucose.  We quantified glucose uptake rate and fermentation product secretion rate using HPLC. The amino acid isotopomer fractions were measured using 2D [¹³C, ²H] HSQC NMR. Flux distributions were computed from simulating isotopomer distribution and then fitting it to the experimental measurements. We found distinctions in central metabolism flux distribution between control and treatment, especially in the TCA cycle. These observations could be coupled with transcriptome data to pinpoint the system bottleneck and identify the important genes responsible to enhance fatty acid tolerance. This project was funded by U.S. National Science Foundation (EEC-0813570).