TRANSITION-METAL REQUIREMENT TO EXPRESS HIGH-LEVEL NAD+-DEPENDENT FORMATE DEHYDROGENASE FROM A SERINE-TYPE METHYLOTROPHIC BACTERIUM

Formate dehydrogenase (EC 1.2.1.2) from an aerobic organism was found to be metal-dependent. This NAD+-dependent enzyme required the presence of tungsten or molybdenum to express high enzyme levels in the facultative methylotrophic Methylobacterium sp. RXM. The apparent V(max) of the reaction increased 22-fold in a tungstate-containing medium when compared with a non-metal-supplemented growth medium. The absence of those metals in the culture medium resulted in the partial loss of an energy-yielding step and approx. 50% decrease in the cell yield was observed. Moreover, formate accumulated in the extracellular medium and culture pH dropped. Tungsten produced a higher stimulation of formate dehydrogenase activity than that obtained with molybdenum for batch cultivation of Methylobacterium sp. RXM.