Evolution and Functional Characterisation of the RH50 Gene from the Ammonia-Oxidizing Bacterium Nitrosomonas europaea

Inserm, U845, Paris, F-75015, France; Université Paris Descartes, Faculté de Medecine René Descartes, Paris, F-75015 France.; Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK; Department of Microbiology, University of Bayreuth, Universitaetsstrasse 30, 95447 Bayreuth, Germany; Inserm, U571, Paris, F-75015, France; Institut Jacques Monod CNRS-UMR 7592, Université Paris 6 et Paris 7; 2, Place Jussieu, 75251 Cedex 05, Paris, France

^* To whom correspondence should be addressed. Email: giorgio.matassi{at}snv.jussieu.fr.

	Abstract

The family of ammonia/um 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 so 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 characterising the NeRh50 protein and the corresponding knockout mutant, we determined that NeRh50 can mediate ammonium uptake. The NeRH50 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 non-orthologous gene displacement.