Disparate oxygen responsiveness of two regulatory cascades that control expression of symbiotic genes in Bradyrhizobium japonicum |
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Authors: | Sciotti Michel-Angelo Chanfon Astrid Hennecke Hauke Fischer Hans-Martin |
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Affiliation: | Institut für Mikrobiologie, Eidgen?ssische Technische Hochschule, CH-8092 Zürich, Switzerland. |
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Abstract: | Two oxygen-responsive regulatory systems controlling numerous symbiotic genes in Bradyrhizobium japonicum were assayed in free-living cultures for their capacity to activate target genes under different oxygen conditions. NifA- and FixLJ-controlled target genes showed disparate relative expression patterns. Induction of NifA-dependent genes was observed only at oxygen concentrations below 2% in the gas phase, whereas that of FixLJ-controlled targets progressively increased when the oxygen concentration was lowered from 21 to 5, 2, or 0.5%. We propose that this reflects a response to a gradient of increasing oxygen deprivation as bacteria invade their host during root nodule development. |
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