Metabolic engineering of Rhizopus oryzae: effects of overexpressing pyc and pepc genes on fumaric acid biosynthesis from glucose.

Fumaric acid, a dicarboxylic acid used as a food acidulant and in manufacturing synthetic resins, can be produced from glucose in fermentation by Rhizopus oryzae. However, the fumaric acid yield is limited by the co-production of ethanol and other byproducts. To increase fumaric acid production, overexpressing endogenous pyruvate carboxylase (PYC) and exogenous phosphoenolpyruvate carboxylase (PEPC) to increase the carbon flux toward oxaloacetate were investigated. Compared to the wild type, the PYC activity in the pyc transformants increased 56%-83%, whereas pepc transformants exhibited significant PEPC activity (3-6 mU/mg) that was absent in the wild type. Fumaric acid production by the pepc transformant increased 26% (0.78 g/g glucose vs. 0.62 g/g for the wild type). However, the pyc transformants grew poorly and had low fumaric acid yields (<0.05 g/g glucose) due to the formation of large cell pellets that limited oxygen supply and resulted in the accumulation of ethanol with a high yield of 0.13-0.36 g/g glucose. This study is the first attempt to use metabolic engineering to modify the fumaric acid biosynthesis pathway to increase fumaric acid production in R. oryzae.