The effect of molybdate and tungstate ions on the metabolic rates and enzyme activities in methanol-grown Methylobacterium sp. RXM

Feed-switching experiments were carried out in steady-state methanol-excess chemostat Methylobacterium sp. RXM cultures at a fixed dilution rate, temperature and pH (0.10 h−1, 30° C and 6.95, respectively). The removal of molybdate from the nutrient supply led to a metabolic energy deficiency reflected in the molar growth yield and biomass values. High carbon conversion efficiency was linked with high formate dehydrogenase (FDH) activity and observed only when either molybdate or tungstate was added to the feed medium. A constant coenzyme ratio NAD+/K-ferri-cyanide linked to FDH activity was found during the enzyme stimulation period following the feed-switching experiment with tungstate addition, which suggests that both activities belong to the same enzyme. Quantitative metabolic responses (carbon conversion efficiency, methanol and O2 consumption rates, CO2 production rate and respiratory quotient) were measured in between steady-states just after the shift in the nutrient supply composition.