Microbial Biosynthesis of Monoterpenoic Acid from Glycerol

Geranic acid, a high-value monoterpenoic acid with wide applications, faces supply constraints from the traditional plant extraction method. This study aims to develop an efficient microbial platform for its sustainable production. We engineered an Escherichia coli host by introducing the heterologous mevalonate pathway and dehydrogenases from Castellaniella defragrans (CdGaDH and CdGeDH) to construct a geranic acid biosynthetic route from glycerol. A critical enhancement was achieved by employing the endogenous dehydrogenase EcAdhP alongside CdGeDH in the wild-type strain. Subsequently, employing the strain based on the CdGeDH-CdGaDH group with deletions in the tnaA and pta genes yielded 1.29 g/L of geranic acid with superior isomeric purity (98.85%) while reducing undesirable byproducts, such as acetic acid and indole. In a 1-L bioreactor, geranic acid was produced under optimized conditions which was subsequently isolated and purified to obtain a pure product. Furthermore, the platform was extended to produce nerolic acid, and the purified geranic acid was further methylated into methyl geranate. This work provides a green method for the sustainable and stereoselective biosynthesis of monoterpenoic acids.