Efficient production of cellobionic acid from cellobiose by genetically modified Pseudomonas taetrolens

Abstract

Pseudomonas taetrolens is one of the most efficient lactobionic acid (LBA)-producing microorganisms. We previously found that it also produced cellobionic acid (CBA) and that quinoprotein glucose dehydrogenase (GDH) from P. taetrolens could convert lactose into LBA. Here, we discovered that GDH could also convert cellobiose into CBA when it was heterologously expressed in Escherichia coli. To enhance the CBA-producing ability of P. taetrolens, we homologously expressed GDH in P. taetrolens, and demonstrated that the intracellular cellobiose-oxidizing activity (1.75 U/μg) and CBA titer (21.4 g/L) of the recombinant P. taetrolens were approximately 54% and 60% higher than those (1.14 U/μg and 13.4 g/L, respectively) of the wild-type P. taetrolens in 12 h flask cultures. We optimized culture conditions of this recombinant strain, such as cellobiose concentration, growth temperature, and cell density of seed culture. Thereafter, we scaled up the CBA production using a 5-L bioreactor under the optimized culture condition determined in flask culture experiments. The CBA production titer, yield, and productivity of the recombinant P. taetrolens strain after batch fermentation were 200 g/L, 95.6%, and 9.52 g/L/h, respectively, which far exceeded those obtained in previous studies. Our study provides important clues to achieve economically feasible production of CBA.