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Journal of Bacteriology, April 2001, p. 2595-2604, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2595-2604.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

A Functional myo-Inositol Dehydrogenase Gene Is Required for Efficient Nitrogen Fixation and Competitiveness of Sinorhizobium fredii USDA191 To Nodulate Soybean (Glycine max [L.] Merr.)

Guoqiao Jiang,1 Ammulu Hari Krishnan,1 Yong-Woong Kim,2 Thomas J. Wacek,3 and Hari B. Krishnan1,4,*

Department of Agronomy1 and Plant Genetics Research Unit, USDA-ARS,4 University of Missouri, Columbia, Missouri 65211; Department of Agricultural Chemistry, Chonnam National University, Kwang-Ju, Korea2; and Urbana Laboratories, St. Joseph, Missouri 645013

Received 25 October 2000/Accepted 11 January 2001

Inositol derivative compounds provide a nutrient source for soil bacteria that possess the ability to degrade such compounds. Rhizobium strains that are capable of utilizing certain inositol derivatives are better colonizers of their host plants. We have cloned and determined the nucleotide sequence of the myo-inositol dehydrogenase gene (idhA) of Sinorhizobium fredii USDA191, the first enzyme responsible for inositol catabolism. The deduced IdhA protein has a molecular mass of 34,648 Da and shows significant sequence similarity with protein sequences of Sinorhizobium meliloti IdhA and MocA; Bacillus subtilis IolG, YrbE, and YucG; and Streptomyces griseus StrI. S. fredii USDA191 idhA mutants revealed no detectable myo-inositol dehydrogenase activity and failed to grow on myo-inositol as a sole carbon source. Northern blot analysis and idhA-lacZ fusion expression studies indicate that idhA is inducible by myo-inositol. S. fredii USDA191 idhA mutant was drastically affected in its ability to reduce nitrogen and revealed deteriorating bacteroids inside the nodules. The number of bacteria recovered from such nodules was about threefold lower than the number of bacteria isolated from nodules initiated by S. fredii USDA191. In addition, the idhA mutant was also severely affected in its ability to compete with the wild-type strain in nodulating soybean. Under competitive conditions, nodules induced on soybean roots were predominantly occupied by the parent strain, even when the idhA mutant was applied at a 10-fold numerical advantage. Thus, we conclude that a functional idhA gene is required for efficient nitrogen fixation and for competitive nodulation of soybeans by S. fredii USDA191.

* Corresponding author. Mailing address: USDA-ARS, 108W Curtis Hall, University of Missouri, Columbia, MO 65211. Phone: (573) 882-8151. Fax: (573) 884-7850. E-mail: KrishnanH{at}missouri.edu.

Journal of Bacteriology, April 2001, p. 2595-2604, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2595-2604.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.