Metabolic Engineering of Candida Tropicalis for the Production of Long–Chain Dicarboxylic Acids

Abstract

We have engineered an industrial strain of the yeast, Candida tropicalis, for the efficient production of long–chain dicarboxylic acids, which are important raw materials for the chemical industry. By sequential disruption of the four genes encoding both isozymes of the acyl–CoA oxidase which catalyzes the first reaction in the β–oxidation pathway, alkane and fatty acid substrates have been successfully redirected to the ω–oxidation pathway. Consequently, the conversion efficiency and chemical selectivity of their terminal oxidation to the corresponding dicarboxylic acids has been improved to 100 percent. The specific productivity of the bioconversion has been increased further by amplification of the cytochrome P450 monooxygenase and NADPH–cyto–chrome reductase genes encoding the rate–limiting ω–hydroxylase in the ω–oxidation pathway. The amplified strains demonstrated increased ω–hydroxylase activity and a 30% increase in productivity compared to the β–oxidation–blocked strain in fermentations. The bioconversion is effective for the selective terminal oxidation of both saturated and unsaturated linear aliphatic substrates with chain–lengths ranging from 12 carbons to 22 carbons and also avoids the undesirable chain modifications associated with passage through the β–oxidation pathway, such as unsaturation, hydroxylation, or chain shortening. It is now possible to efficiently produce a wide range of previously unavailable saturated and unsaturated dicarboxylic acids with a high degree of purity.