Toward A Chemical Revolution: Solving Biocatalyst Inhibition for the Production of Fatty Acids

Cracking crude oil into light olefins gave birth to chemical industry in the early 1900s. Olefins were used to synthesize a variety of chemical compounds that were marketed for specific applications. The combination of depleting petroleum reserves and unstable crude oil market prices gives rise to the need for a sustainable raw base for the chemical industry. Short Chain Fatty Acids (SCFAs) produced in high titer by biocatalysts are great candidates as a biorenewable feedstock for the chemical industry. Small organic molecules produced by biocatalysts can be defunctionalized by traditional chemical catalysis to synthesize a plethora of precursor molecules used in the chemical industry. SCFAs are intermediate metabolites that are used within the cell as substrates for producing longer chain fatty acids for membrane components. Unfortunately, SCFAs are inhibitory to cell growth, thereby the production of SCFAs via biocatalyst is difficult. In this work, the minimum inhibitor concentration (MIC) under anaerobic conditions for hexanoic (C6), octanoic (C8), and decanoic acids (C10) are determined to be 2.5 mM, 5 mM, and 10 mM respectively. The MIC under aerobic condtions are 5mM, 10mM, and 20mM for C6, C8, and C10 respectively. The base Escherichia coli biocatalyst used, MG1655, is comparable to other industrial strains 8739 and 9637. Under aerobic conditions, the cells are able to metabolize the SCFAs in the growth medium. Deletion mutants MG1655∆fadAB, MG1655∆fadIJ, MG1655∆fadABIJ show that the genes encoding the fatty acid degradation pathway aid cell growth under aerobic conditions. The deletion mutant MG1655∆fadR shows that the gene fadR inhibits the fatty acid degradation pathway leading to cell growth inhibition.