Nitrogen fixation by the unicellular cyanobacterium Gloeothece. Nitrogenase synthesis is only transiently repressed by oxygen

Reconciling the incompatible: N2 fixation And O2

“…In addition, the disappearance of residual activity following inhibition of nitrogenase synthesis by addition of NH^^ was much more rapid in air than under N,^ (Tozum et al, 1977). Furthermore, Od oes not permanently inhibit nitrogenase synthesis in Gloeotheee (Mullineaux, Chaplin & Gallon, 1983;Maryan et al, 19866;Page & Gallon, 1992). Transfer of aerobically grown cultures of Gloeotheee to O^iCOa (99-97:0-03, by vol.)…”

DNA topoisomerases in Gloeothece (Nägeli) sp. ATCC 27152: a role in N2 fixation?

“…In marked contrast, inhibition of nitrogenase synthesis following transfer of aerobically grown cultures of Gloeothece to O2: COg (99-97:0-03, by vol.) was only transient (Table 4; Maryan et aL, 1986), and was exactly paralleled by a transient predominance of DNA topoisomerase I activity over that of DNA gyrase (Table 2a). It is therefore possible that the short-lived inhibition by Oj of nitrogenase synthesis in Gloeothece is a result of a transient relaxation of one or more of the nif genes caused by a perturbation in the relative activities of DNA gyrase and DNA topoisomerase I.…”

“…The unicellular cyanobacterium Gloeothece (Nageli) is unusual, if not unique, among diazotrophs in that nitrogenase synthesis is only transiently, not permanently, repressed by Oj (Maryan et al, 1986). Furthermore, nitrogenase is synthesized in both aerobically and microaerobically grown cultures, though the rate of synthesis may be slightly greater when the prevailing concentration of Og is very low (Gallon & Chaplin, 1988).…”

“…Nitrogenase synthesis was measured as incorporation of radioactivity from Na2^*SO4 into the MoFeprotein of Gloeothece nitrogenase by the radioimmunoassay of Maryan et al (1986), as modified by .…”

How is nitrogenase regulated by oxygen?

“…Regulation of nitrogenase synthesis by 0 2 is less well understood than that by fixed N for the following reasons: (1) the O 2 lability of nitrogenase, (2) the technical sophistication required to measure and maintain a given dissolved oxygen concentration (section 3), (3) the absence of a straightforward method for selecting oxygen constitutive mutants (section 6.7) and (4) the relative lack of knowledge relating to the molecular [115] nif mRNA [19,116,117] nitrogenase polypeptides [114,118] nifH-lac a [119] nitrogenase polypeptides [120] nitrogenase polypeptides [121,122] nitrogenase polypeptides [123] nitrogenase polypeptides [124] nifIf mRNA [125] nitrogenase component I [126] polypeptides biology of oxygen regulation (section 6.6) compared to that of N regulation by the ntr control system [110][111][112]. Nevertheless, progress has been made, particularly with the facultative anaerobe .…”