Ammonium and Molybdenum Regulation of the Molybdenum Nitrogenase and the Alternative Nitrogenase in Rhodobacter Capsulatus

Drepper, Thomas; Groß, Silke; Masepohl, Bernd; Klipp, Werner

doi:10.1007/0-306-47615-0_62

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“…Regulation of glnK expression Like many proteobacteria, R. capsulatus contains two P IIencoding genes, glnB and glnK (Drepper et al, 2000;Masepohl et al, 2002). The R. capsulatus glnK gene region was isolated by a PCR-based strategy (Methods).…”

Section: Resultsmentioning

confidence: 99%

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Role of GlnB and GlnK in ammonium control of both nitrogenase systems in the phototrophic bacterium Rhodobacter capsulatus

et al. 2003

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In most bacteria, nitrogen metabolism is tightly regulated and P II proteins play a pivotal role in the regulatory processes. Rhodobacter capsulatus possesses two genes (glnB and glnK ) encoding P II -like proteins. The glnB gene forms part of a glnB-glnA operon and the glnK gene is located immediately upstream of amtB, encoding a (methyl-) ammonium transporter. Expression of glnK is activated by NtrC under nitrogen-limiting conditions. The synthesis and activity of the molybdenum and iron nitrogenases of R. capsulatus are regulated by ammonium on at least three levels, including the transcriptional activation of nifA1, nifA2 and anfA by NtrC, the regulation of NifA and AnfA activity by two different NtrC-independent mechanisms, and the post-translational control of the activity of both nitrogenases by reversible ADP-ribosylation of NifH and AnfH as well as by ADP-ribosylation independent switch-off. Mutational analysis revealed that both P II -like proteins are involved in the ammonium regulation of the two nitrogenase systems. A mutation in glnB results in the constitutive expression of nifA and anfA. In addition, the post-translational ammonium inhibition of NifA activity is completely abolished in a glnB-glnK double mutant. However, AnfA activity was still suppressed by ammonium in the glnB-glnK double mutant. Furthermore, the P II -like proteins are involved in ammonium control of nitrogenase activity via ADP-ribosylation and the switch-off response. Remarkably, in the glnB-glnK double mutant, all three levels of the ammonium regulation of the molybdenum (but not of the alternative) nitrogenase are completely circumvented, resulting in the synthesis of active molybdenum nitrogenase even in the presence of high concentrations of ammonium.

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Section: Resultsmentioning

confidence: 99%

“…Preliminary results concerning the role of R. capsulatus GlnB and GlnK in the regulation of nitrogen fixation were presented at the 12th and 13th International Congress on Nitrogen Fixation (Drepper et al, 2000;Groß et al, 2002;.…”

Section: Introductionmentioning

confidence: 99%