Role of the nifQ gene product in the incorporation of molybdenum into nitrogenase in Klebsiella pneumoniae

Abstract

NifQ- mutants of K. pneumoniae are defective in N2 fixation due to an elevated requirement for Mo. When mM concentrations of molybdate were added to the medium, the effects of the nifQ mutations were suppressed. NifQ- mutants were not impaired in the uptake of molybdate, but molybdate accumulation was defective in these mutants. All of the nif-coded proteins were present in NifQ- cells derepressed in the absence of Mo. Mo-activatable nitrogenase component I was found at the same level observed in the wild type. Mo thus does not play a role in nif expression or in the short-term stability of nif-coded proteins. The defect in NifQ- mutants was in the incorporation of Mo into nitrogenase component I. The nifQ gene product acts together with the products of nifB, nifN and nifE in the biosynthesis of the Fe-Mo cofactor of nitrogenase.