Tim McCubbin, Veronica Martinez, Lars Nielsen, Esteban Marcellin*


Australian Institute of Bioengineering and Nanotechnology
Corner College and Cooper Rds (Bldg 75)
The University of Queensland
Brisbane, Queensland, Australia



A unique, yet poorly understood metabolism results in propionibacteria being naturally high producers of propionate (PA) and candidate organisms for its industrial-scale biological production. However, to be competitive with traditional petrochemical PA synthesis routes a yield of 0.6 g PA/g glucose is required1, which surpasses the capabilities of the best natural producing strain, P. acidipropionici 55737. While resistant to rational engineering approaches, higher producing native strains are still susceptible to random mutagenesis techniques such as genome-shuffling. Recently, we successfully used genome-shuffling to create a strain, known as WGS7, with superior PA productivity and a yield exceeding targets for an economically viable fermentation2. Sequencing of WGS7 showed its genome was highly similar to P. acidipropionici 55737 and the underlying cause of the improved phenotype remained elusive. To unlock the mystery behind WGS7, a battery of systems biology approaches were applied. Initially a metabolic model was generated that described the entirety of metabolism and subsequently reduced and curated to describe the most relevant, thermodynamically consistent reactions considering proteomic and metabolomics data. This reduced model could then be used to estimate the instantaneous metabolic fluxes throughout the fermentation for both the wildtype and mutant strains using a technique called dynamic metabolic flux analysis. This in-depth analysis gave keen insights into the differential use of metabolic pathways between the two strains, particularly highlighting the role of the TCA cycle to enhance PA production and overcome its inhibitory influence on metabolism. The results not only serve to guide future genetic engineering work but increase our understanding of the complex, dynamic propionibacteria fermentation.

1.Rodriguez, B.A.; Stowers, C.C.; Pham, V.; Cox, B.M. The production of propionic acid, propanol and propylene sugar fermentation: An industrial perspective on the progress, technical challenges and future outlook. Green Chem. 2014, 41, 837-852.

2.Luna-Flores, C.H.; Stowers, C.C.; Cox, B.; Nielsen, L.K.; Marcellin, E. Scalable and economical process for propionic acid biosynthesis. Biotechnol. Biofuels 2017, Submitted