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Journal of Bacteriology, April 1999, p. 1994-2000, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The Presence of ADP-Ribosylated Fe Protein of Nitrogenase in Rhodobacter capsulatus Is Correlated with Cellular Nitrogen Status

Alexander F. Yakunin,1,2 Tatyana V. Laurinavichene,2 Anatoly A. Tsygankov,2 and Patrick C. Hallenbeck1,*

Département de Microbiologie et Immunologie, Université de Montréal, Succursale Centre-ville, Montréal, Québec H3C 3J7, Canada,1 and Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region, Russia2

Received 23 October 1998/Accepted 25 January 1999

The photosynthetic bacterium Rhodobacter capsulatus has been shown to regulate its nitrogenase by covalent modification via the reversible ADP-ribosylation of Fe protein in response to darkness or the addition of external NH4+. Here we demonstrate the presence of ADP-ribosylated Fe protein under a variety of steady-state growth conditions. We examined the modification of Fe protein and nitrogenase activity under three different growth conditions that establish different levels of cellular nitrogen: batch growth with limiting NH4+, where the nitrogen status is externally controlled; batch growth on relatively poor nitrogen sources, where the nitrogen status is internally controlled by assimilatory processes; and continuous culture. When cultures were grown to stationary phase with different limiting concentrations of NH4+, the ADP-ribosylation state of Fe protein was found to correlate with cellular nitrogen status. Additionally, actively growing cultures (grown with N2 or glutamate), which had an intermediate cellular nitrogen status, contained a portion of their Fe protein in the modified state. The correlation between cellular nitrogen status and ADP-ribosylation state was corroborated with continuous cultures grown under various degrees of nitrogen limitation. These results show that in R. capsulatus the modification system that ADP-ribosylates nitrogenase in the short term in response to abrupt changes in the environment is also capable of modifying nitrogenase in accordance with long-term cellular conditions.

* Corresponding author. Mailing address: Département de Microbiologie et Immunologie, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal, Québec H3C 3J7, Canada. Phone: (514) 343-6278. Fax: (514) 343-5701. E-mail: patrick.hallenbeck{at}umontreal.ca.

Journal of Bacteriology, April 1999, p. 1994-2000, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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