Regulation of nitrogen fixation in the phototrophic purple bacterium Rhodobacter capsulatus

  • Masepohl B
  • Drepper T
  • Paschen A
 et al. 
  • 3

    Readers

    Mendeley users who have this article in their library.
  • N/A

    Citations

    Citations of this article.

Abstract

In R. capsulatus synthesis and activity of the molybdenum and the alternative nitrogenase is controlled at three levels by the environmental factors ammonium, molybdenum, light, and oxygen. At the first level, transcription of the nifA1, nifA2, and anfA genes--which encode the transcriptional activators of all other nif and anf genes, respectively--is controlled by the Ntr system in dependence on ammonium availability. Mutations in ginB (coding for the signal transduction protein PII) result in significant expression of nifA and anfA in the presence of ammonium. In contrast to GlnB, the PII-paralogue GlnK is not involved in the Ntr signal transduction mechanism. In addition to ammonium control, transcription of anfA is inhibited by traces of molybdenum via the molybdate-dependent repressor proteins MopA and MopB. At the second level of regulation, activity of NifA1, NifA2, and AnfA is inhibited by ammonium in an NtrC-independent manner. This post-translational ammonium control of NifA activity is partially released in the absence of GlnK, and completely abolished in a glnB/glnK double mutant. In contrast, AnfA activity is still inhibited by ammonium in the glnB/glnK mutant background. At the third level of regulation, both GlnB and GlnK as well as the (methyl)-ammonium transporter AmtB are involved in ammonium control of the DraT/DraG system, which mediates reversible ADP-ribosylation of both nitrogenase reductases (NifH and AnfH) in response to changes in ammonium availability or light intensity. Most remarkably, in a glnB/glnK double mutant ammonium control of the molybdenum (but not of the alternative) nitrogenase is completely relieved, leading to synthesis of active nitrogenase in the presence of high concentrations of ammonium.

Author-supplied keywords

  • *Gene Expression Regulation
  • Bacteria/genetics/*metabolism
  • Bacterial
  • Molybdenum/metabolism
  • Nitrogen Fixation/genetics/*physiology
  • Nitrogenase/genetics/metabolism
  • Rhodobacter capsulatus/genetics/*metabolism

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document

Authors

  • B Masepohl

  • T Drepper

  • A Paschen

  • S Gross

  • A Pawlowski

  • K Raabe

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free