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Journal of Bacteriology, August 2002, p. 4081-4088, Vol. 184, No. 15
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.15.4081-4088.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

AmtB Is Necessary for NH4+-Induced Nitrogenase Switch-Off and ADP-Ribosylation in Rhodobacter capsulatus{ddagger}

Alexander F. Yakunin,{dagger} and Patrick C. Hallenbeck*

Département de Microbiologie et Immunologie, Université de Montréal, Succursale Centre-ville, Montréal, Québec H3C 3J7, Canada

Received 1 March 2002/ Accepted 3 May 2002

Rhodobacter capsulatus possesses two genes potentially coding for ammonia transporters, amtB and amtY. In order to better understand their role in the physiology of this bacterium and their possible significance in nitrogen fixation, we created single-knockout mutants. Strains mutated in either amtB or amtY did not show a growth defect under any condition tested and were still capable of taking up ammonia at nearly wild-type rates, but an amtB mutant was no longer capable of transporting methylamine. The amtB strain but not the amtY strain was also totally defective in carrying out ADP-ribosylation of Fe-protein or the switch-off of in vivo nitrogenase activity in response to NH4+ addition. ADP-ribosylation in response to darkness was unaffected in amtB and amtBY strains, and glutamine synthetase activity was normally regulated in these strains in response to ammonium addition, suggesting that one role of AmtB is to function as an ammonia sensor for the processes that regulate nitrogenase activity.

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

{ddagger} Dedicated to the memory of Werner Klipp.

{dagger} Permanent address: Institute of Basic Biological Problems, Russian Academy of Sciences, Puschino, Russia.

Journal of Bacteriology, August 2002, p. 4081-4088, Vol. 184, No. 15
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.15.4081-4088.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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