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Applied and Environmental Microbiology, January 2004, p. 535-541, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.535-541.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Bradyrhizobium elkanii rtxC Gene Is Required for Expression of Symbiotic Phenotypes in the Final Step of Rhizobitoxine Biosynthesis

Shin Okazaki, Masayuki Sugawara, and Kiwamu Minamisawa*

Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan

Received 28 August 2003/ Accepted 10 October 2003

We disrupted the rtxC gene on the chromosome of Bradyrhizobium elkanii USDA94 by insertion of a nonpolar aph cartridge. The rtxC mutant, designated {Delta}rtxC, produced serinol and dihydrorhizobitoxine but no rhizobitoxine, both in culture and in planta. The introduction of cosmids harboring the rtxC gene into the {Delta}rtxC mutant complemented rhizobitoxine production, suggesting that rtxC is involved in the final step of rhizobitoxine biosynthesis in B. elkanii USDA94. Glycine max cv. Lee inoculated with {Delta}rtxC or with a null mutant, {Delta}rtx::{Omega}1, showed no foliar chlorosis, whereas the wild-type strain USDA94 caused severe foliar chlorosis. The two mutants showed significantly less nodulation competitiveness than the wild-type strain on Macroptilium atropurpureum. These results indicate that dihydrorhizobitoxine, the immediate precursor of the oxidative form of rhizobitoxine, has no distinct effect on nodulation phenotype in these legumes. Thus, desaturation of dihydrorhizobitoxine by rtxC-encoded protein is essential for the bacterium to show rhizobitoxine phenotypes in planta. In addition, complementation analysis of rtxC by cosmids differing in rtxC transcription levels suggested that rhizobitoxine production correlates with the amount of rtxC transcript.

* Corresponding author. Mailing address: Graduate School of Life Sciences, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577, Japan. Phone: 81-22-217-5684. Fax: 81-22-263-9845. E-mail: kiwamu{at}ige.tohoku.ac.jp.

Applied and Environmental Microbiology, January 2004, p. 535-541, Vol. 70, No. 1
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.1.535-541.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Itakura, M., Tabata, K., Eda, S., Mitsui, H., Murakami, K., Yasuda, J., Minamisawa, K. (2008). Generation of Bradyrhizobium japonicum Mutants with Increased N2O Reductase Activity by Selection after Introduction of a Mutated dnaQ Gene. Appl. Environ. Microbiol. 74: 7258-7264 [Abstract] [Full Text]  
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