Pathways of Energy Metabolism Required for Phenotypic Expression of Nif+Kp Genes in Escherichia Coli

Abstract

In E. coli K12 (F'nif+ KP) hybrids, electron-transport-dependent phosphorylation is not necessary for anaerobic nitrogen fixation, and substrate level phosphorylation can provide sufficient ATP from glucose for nitrogenase activity, The fumarate-reduction system, however, is essential in these hybrids for the transfer of electrons to nitrogenase, This system is probably also involved in maintaining the membrane in the energized state, thereby allowing nitrogen fixation to occur, The nitrate-reduction system, which can energize the membrane like the fumarate-reduction system, is not necessary for nitrogenase activity in the E. coli KI2(F'nif+ Kp) hybrids, However, two nitrate reductase genes, chlA, and chlB, are essential for inhibition of nitrogen fixation by nitrate. Moreover, nitrate inhibits nitrogenase activity and this inhibition is most probably effected through a regulator factor coded by chlA and chlB,

Fnr Is Required for NifL-Dependent Oxygen Control of nif Gene Expression in Klebsiella pneumoniae

“…Attractive hypothetical candidates for the physiological electron donor for NifL are components of the anaerobic electron transport system (Fig. 5), particularly the electron transport system to fumarate, whose transcription under anaerobic conditions is directly dependent on Fnr activation (1,24,34,38). Preliminary data, which indicate that K. pneumoniae NifL under anaerobic conditions is membrane associated, whereas in the presence of oxygen NifL is in the cytosolic fraction, support this model (Klopprogge and Schmitz, unpublished).…”

nifgenes in alien backgrounds

“…The phenotype of narD~ hybrids resembles that of the ni/Q mutation in that nif expression occurs at relatively high molybdate concentration (Imperial et al 1984). Skotnicki & Rolfe (1979) reported that far mutants of E. coli did not express Kp nif on FN68 and proposed that nif regulation in response to Oa might be linked to general control of the synthesis of redox enzymes. However, Hill (1985) reinvestigated the matter with the more stable pRDl and obtained normal nif expression in five far mutants of E. coli.…”

Regulation of nitrogen fixation in Klebsiella pneumoniae: NifL, one protein transducing two environmental signals to the nif-transcriptional activator NifA

“…Attractive hypothetical candidates for the physiological electron donor for NifL are components of the anaerobic electron transport system (Fig. 9), particularly the electron transport system to fumarate, whose transcription under anaerobic conditions is directly dependent on Fnr activation (Ackrell, 2000;Manodori et al, 1992;Skotnicki and Rolfe, 1979;Van Hellemond and Tielens, 1994).…”