Integrating metabolic and evolutionary engineering for enhanced propionic acid production under cross stress: a multi-omics perspective

Abstract Background: Propionic acid (PA), a potential building block for C3-based bulk chemicals, is used as a food preservative and antifungal agent because of the antimicrobial properties of its calcium-, potassium-, and sodium salts, as well as in the manufacture of pharmaceuticals, perfumes, pesticides and fungicides. However, industrial development of PA is seriously inhibited by oxygen stress, acid stress and glucose-induced osmotic stress concentration on account of the characteristic of Propionibacterium acidipropionici. To alleviate inhibition and increase PA production, enhancement P. acidipropionici tolerance to cross stress may be an effective strategy. Results: In this study, we first performed a combination of metabolic engineering (deletion of ldh and poxB and overexpression of mmc) with evolutionary engineering (selection under oxygen stress, acid stress and osmotic stress) in P. acidipropionici. The results indicated the mutants received superior physiological activity, especially the mutant III exhibited steady 1.5-3.5 folds higher growth property and further 37.1% PA titer and 37.8% PA productivity increase than the wildtype. Moreover, omics analysis revealed the determinants such as Dps , GroES , dnaK , ADI and GAD referred to the acid adaptation of microbes were positively mobilized. ABC-type glycine betaine referred to the adaptability to osmotic stress was detected to be 2-4 folds up-regulated. More than 2-fold down-regulation of NADH oxidase and almost 3-fold up-regulation of SOD and POD were observed in three mutants. Moreover, an approximately 2.5-fold upregulation of mmc was also found. Conclusion: The multi-omics analysis revealed the multidirectional variation tendency of P. acidipropionici under cross stress and provided in-depth insights into the mechanism of tolerance and high production of PA, which layed the foundation for construction of microbial cell factories.