Microbial production of propionic acid through a novel β-alanine route

Prof. Sang Yup Lee’s group at KAIST has developed a novel vitamin B₁₂-independent biosynthetic pathway for propionic acid production via a β-alanine route, achieving the highest reported titer of heterologous propionic acid production to date. By systematically engineering Escherichia coli and Corynebacterium glutamicum, the team established a sustainable and efficient microbial platform that overcomes the intrinsic limitations of conventional propionigenic bacteria. The study was published in January 2026 (Microbial production of propionic acid through a novel β -alanine route, Metabolic Engineering, 93, 219–231 (2026)).

Propionic acid is an important three-carbon (C3) platform chemical used in food preservation, pharmaceuticals, herbicides, and thermoplastic production. Current industrial production depends largely on the petrochemical Reppe process, raising concerns regarding fossil resource dependence and environmental sustainability. Although native propionigenic microorganisms can synthesize propionic acid biologically, their slow growth, strict anaerobic requirements, and limited genetic engineering tools restrict industrial scalability. To address these constraints, the KAIST team designed an alternative metabolic route based on β-alanine as a key intermediate.

The research team designed the pathway into two distinct modules: an upstream β-alanine-forming module and a downstream propionic acid-forming module. Through systematic enzyme screening and optimization of metabolic flux, the engineered E. coli strain achieved 14.8 g/L of propionic acid. To address product toxicity observed in E. coli, which showed significant growth inhibition above 20 g/L, the pathway was subsequently introduced into C. glutamicum, a host with superior organic acid tolerance. By incorporating the downstream pathway into a previously engineered β-alanine-overproducing strain and implementing additional strategies including deletion of acetate-producing genes (ack-pta), disruption of propionate degradation pathways (prpD2B2C2), and evaluation of native CoA transferase and reductase candidates, the engineered strain achieved 47.4 g/L of propionic acid in fed-batch fermentation. This represents the highest reported titer for heterologous propionic acid biosynthesis.

This study establishes a scalable and vitamin B₁₂-independent strategy for sustainable propionic acid production from renewable carbon sources. By integrating pathway modularization, enzyme optimization, metabolic flux redistribution, and host strain selection, the work provides a general framework for the development of efficient microbial cell factories for C3 platform chemicals.

“This research establishes a promising β-alanine-based platform that operates independently of expensive cofactors like vitamin B₁₂, offering a significant advantage for cost-effective industrial scale-up,” said Sang Yup Lee, the corresponding author and a professor in the Department of Chemical and Biomolecular Engineering at KAIST.

“Systematic optimization of metabolic flux and pathway coordination enabled us to reach record-level titers, highlighting the industrial potential of the β-alanine route and this propionyl-CoA platform can be further extended to the biosynthesis of various other value-added compound,” said the co-first author, Da-Hee Ahn.

This work was supported by the development of platform technologies of microbial cell factories for the next-generation biorefineries project (2022M3J5A1056117) and by the development of advanced synthetic biology source technologies for leading the biomanufacturing industry project (RS-2024-00399424) from National Research Foundation supported by the Korean Ministry of Science and ICT.