The consequence of stimulating glucose dehydrogenase activity by the addition of PQQ on metabolite production by Agrobacterium radiobacter NCIB 11883

Summary

Agrobacterium radiobacter NCIB 11 883 does not produce gluconate under conditions of glucose excess in batch or continuous culture. However, the addition of micromolar concentrations of pyrrolo quinoline quinone (PQQ) to fermentation media resulted in rapid excretion of gluconate by batch and continuous cultures. This rapid dehydrogenation of glucose was found in cells grown under carbon and nitrogen limitation and is constitutive which suggests that the only reason why this activity is not normally expressed is due to the inability of the organism to synthesize the prosthetic group (PQQ) of the glucose dehydrogenase enzyme.

Although the addition of PQQ to batch and continuous cultures caused a very rapid specific rate of gluconate production (0.6–1.1 g gluconate g^-1 dry wt. h^-1) the rate of exopolysaccharide production remained unaltered. Indeed, when the rates of substrate and oxygen uptake are corrected for the rate of gluconate production in the presence of PQQ there appears to be little physiological consequence as a result of this oxidation.