Fermentative production of short-chain fatty acids and methyl ketones in Escherichia coli

Abstract

Dependence on petroleum for fuels is a well-known issue in the United States today. However, petroleum is also used to produce a broad range of chemicals that are used in applications such as plastics, fragrances, surfactants, detergents, food additives, and pharmaceuticals. As the world's supply of petroleum dwindles, we must look to another method of procuring these chemicals. Biorenewable chemical production attempts to fill this void. Shortchain fatty acids and ketones are desirable precursors to many of these industrially relevant chemicals. Short-chain fatty acids are precursors to alpha-olefins, which are used as lubricants and surfactants in a variety of industries, including the automotive industry. They can also be used as precursors to fatty alcohols, which have potential applications as biodiesel. Methyl ketones are also a class of chemicals with many industrial applications. Butanone is a common industrial solvent, while 4-hydroxybutanone is used in pesticides, terpenoids, and most importantly, is an intermediate in the production of doxorubicin, an anticancer agent. Here we report the biorenewable production of short-chain fatty acids and methyl ketones from fermentation in Escherichia coli. A series of synthetic constructs were made to produce the desired metabolites utilizing glucose as the feedstock. Butyrate was produced at 9.670 g/L, hexanoate at 1.963 g/L, and octanoate at 0.216 g/L. In addition, 0.201 g/L of valerate was produced. Heptanoate production by fermentation in E. coli was reported for the first time, reaching a titer of 0.008 g/L. 4-hydroxy-2-butanone was produced by fermentation at a titer of 2.5 mM. To our knowledge this is the first report of production of 4-hydroxy-2-butanone by microbial fermentation.