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Applied and Environmental Microbiology, March 2003, p. 1527-1531, Vol. 69, No. 3
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.3.1527-1531.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Fnr Is Involved in Oxygen Control of Herbaspirillum seropedicae N-Truncated NifA Protein Activity in Escherichia coli

Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, Curitiba, PR 81531-990, Brazil

Received 5 July 2002/ Accepted 2 December 2002

Herbaspirillum seropedicae is an endophytic diazotroph belonging to the ß-subclass of the class Proteobacteria, which colonizes many members of the Gramineae. The activity of the NifA protein, a transcriptional activator of nif genes in H. seropedicae, is controlled by ammonium ions through its N-terminal domain and by oxygen through mechanisms that are not well understood. Here we report that the NifA protein of H. seropedicae is inactive and more susceptible to degradation in an fnr Escherichia coli background. Both effects correlate with oxygen exposure and iron deprivation. Our results suggest that the oxygen sensitivity and iron requirement for H. seropedicae NifA activity involve the Fnr protein.