Autoregulation of nitrogenase expression in Klebsiella pneumoniae

Abstract

An investigation into the influence of N, on the expression of Klebsiella pneumoniae nitrogenase has led to a reassessment of the role of the nitrogenase MoFe protein in autoregulation. Anaerobic derepression of nitrogenase (C,H,-reducing) activity, of Nif D and K polypeptides, and of nifH-/ac expression, following the removal of excess NH; , were greater under N, than Ar. This enhancement occurred in Nif+ but not in Nif-strains, and in Nif+ strains was prevented by CZH, , an inhibitor of N, fixation. Thus N, fixation is important for maintaining derepression. Derepression of nifH-lac under Ar in various Nif' and Nif-strains (including NifH-, NifD-, NifB-and NifL-mutants) and of wild-type lac under N, or Ar in a Nif' strain were measured to investigate the regulation. The mechanism regulating the enhancement under N, neither involved the MoFe protein of nitrogenase, as proposed by Dixon et a/. (1980, Nature 286, 12&132)# nor the nifL product, but was probably due to a general upgrading of the N status. Moreover, during batch growth limited by a non-repressing fixed N source, the levels of nifH-lac expression in the Nif+ and Nif-strains suggested that the nifH gene product (or Fe protein) may have a positive autoregulatory function.

Nitrogen Fixation Genes and Nitrogenase Activity of the Non-Heterocystous Cyanobacterium <i>Thermoleptolyngbya</i> sp. O-77

“…In previous studies ( 12 , 18 , 45 ), the induction of nitrogenase activity in cells was performed under various N 2 gas phases; however, the optimal N 2 content has not yet been adequately examined. In order to establish optimal induction conditions for nitrogenase in Tl .…”

“…In the case of heterocystous cyanobacteria such as Anabaena variabilis and Nostoc spongiaeforme , nitrogenase induction was stronger under the culture conditions of argon-based gas mixtures (Ar/CO 2 =99/1 [v/v%]) than N 2 -based gas mixtures (N 2 /CO 2 =99/1 [v/v%]) ( 45 ). In non-cyanobacteria, the nitrogenase activity of Klebsiella pneumoniae was weaker under the conditions of N 2 -based gas mixtures (N 2 /CO 2 = 99/1 [v/v%]) than argon-based gas mixtures (Ar/CO 2 = 99/1 [v/v%]) ( 12 ). These findings are consistent with our experimental results, suggesting that the N 2 concentration in culture medium significantly affected the induction of nitrogenase activity by the thermophilic cyanobacterium of Tl.…”

FeMo cofactor biosynthesis in a nifE − mutant of Rhodobacter capsulatus

“…It is interesting to note that the observation of a dramatic increase in nitrogenase activity on cell cultivation under N 2 is not unprecedented. For the K. pneumoniae wild‐type strain, it has been shown that the rate of nitrogenase synthesis is increased by a factor of ≈ 2.5 under N 2 compared with the rate obtained with serine‐grown cells under Ar [54].…”

N2 Fixation by non-heterocystous cyanobacteria1

“…In diazotrophs, nitrogenase synthesis is derepressed under conditions of nitrogen limitation. N 2 is not an inducer of nitrogenase synthesis, though sustained derepression of nitrogenase depends on active N 2 fixation in order to maintain general nitrogen status and thereby allow protein synthesis to continue [168]. In cyanobacteria that can fix N 2 aerobically, nitrogenase synthesis occurs in the presence of air.…”