Scalable propionic acid production using Cutibacterium acnes ZW-1: Insights into substrate and pH-driven carbon flux

An acid-resistant Cutibacterium acnes ZW-1 was isolated from human skin, and propionic acid (PA) production under different substrate and pH conditions was studied. When the molar ratio of lactic acid (LA) to acetic acid (AA) was 7:1 and the pH was 6.5, the PA concentration could reach 64.84 mM. Meanwhile, the index analysis and enzyme activity revealed that the PA carbon flux was 59 %, the PA electronic efficiency reached 79 %, and the propionyl-CoA carboxylase activity was 1.075 mmol·mg protein^-1. Considering the competition between AA/PA production and biomass synthesis, although the slightly acidic pH (<6.5) would promote the flow of carbon to PA, its concentration was severely inhibited due to the limitation of biomass. Further scale-up verification in an automated bioreactor indicated that PA production improved, up to 83.31 mM, and the production rate reached 1.066 g·L^-1·d^-1. This work may provide support for the industrial application of PA bioproduction.