An end-to-end pipeline for succinic acid production at an industrially relevant scale using Issatchenkia orientalis

Microbial production of succinic acid (SA) at an industrially relevant scale has been hindered by high downstream processing costs arising from neutral pH fermentation for over three decades. Here, we metabolically engineer the acid-tolerant yeast *Issatchenkia orientalis* for SA production, attaining the highest titers in sugar-based media at low pH (pH 3) in fed-batch fermentations, i.e., 109.5 g/L in minimal medium and 104.6 g/L in sugarcane juice medium. We further perform batch fermentation using sugarcane juice medium in a pilot-scale fermenter (300 L) and achieve 63.1 g/L of SA, which can be directly crystallized with a yield of 64.0%. Finally, we simulate an end-to-end low-pH SA production pipeline, and techno-economic analysis and life cycle assessment indicate our process is financially viable and can reduce greenhouse gas emissions by 34–90% relative to fossil-based production processes. We expect *I. orientalis* can serve as a general industrial platform for production of organic acids.

Vinh G. Tran, Somesh Mishra, Sarang S. Bhagwat, Saman Shafaei, Yihui Shen, Jayne L. Allen, Benjamin A. Crosly, Shih-I Tan, Zia Fatma, Joshua D. Rabinowitz, Jeremy S. Guest, Vijay Singh, Huimin Zhao