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Evolution and Functional Characterization of the RH50 Gene from the Ammonia-Oxidizing Bacterium Nitrosomonas europaea ^,

INSERM, U845, Paris F-75015, France,¹ Université Paris Descartes, Faculté de Medecine René Descartes, Paris F-75015, France,² Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich NR4 7UH, United Kingdom,³ Department of Microbiology, University of Bayreuth, Universitaetsstrasse 30, 95447 Bayreuth, Germany,⁴ INSERM, U571, Paris F-75015, France,⁵ Institut Jacques Monod, CNRS-UMR 7592, Université Paris 6 et Paris 7, 2 Place Jussieu, 75251 Cedex 05, Paris, France⁶

Received 10 July 2007/ Accepted 4 September 2007

The family of ammonia and ammonium channel proteins comprises the Amt proteins, which are present in all three domains of life with the notable exception of vertebrates, and the homologous Rh proteins (Rh50 and Rh30) that have been described thus far only in eukaryotes. The existence of an RH50 gene in bacteria was first revealed by the genome sequencing of the ammonia-oxidizing bacterium Nitrosomonas europaea. Here we have used a phylogenetic approach to study the evolution of the N. europaea RH50 gene, and we show that this gene, probably as a component of an integron cassette, has been transferred to the N. europaea genome by horizontal gene transfer. In addition, by functionally characterizing the Rh50_Ne protein and the corresponding knockout mutant, we determined that NeRh50 can mediate ammonium uptake. The RH50_Ne gene may thus have replaced functionally the AMT gene, which is missing in the genome of N. europaea and may be regarded as a case of nonorthologous gene displacement.

Published ahead of print on 5 October 2007.

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