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Journal of Bacteriology, August 2004, p. 5384-5391, Vol. 186, No. 16
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.16.5384-5391.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Indole-3-Acetic Acid Biosynthesis Is Deficient in Gluconacetobacter diazotrophicus Strains with Mutations in Cytochrome c Biogenesis Genes

Sunhee Lee,^1, M. Flores-Encarnación,² M. Contreras-Zentella,² L. Garcia-Flores,² J. E. Escamilla,² and Christina Kennedy^1*

Division of Plant Pathology and Microbiology, Department of Plant Sciences, The University of Arizona, Tucson, Arizona 85721,¹ Instituto de Fisiologia Celular, Universidad Nacional Autonoma de Mexico, Mexico D.F., Mexico²

Received 4 May 2004/ Accepted 17 May 2004

Gluconacetobacter diazotrophicus is an endophyte of sugarcane frequently found in plants grown in agricultural areas where nitrogen fertilizer input is low. Recent results from this laboratory, using mutant strains of G. diazotrophicus unable to fix nitrogen, suggested that there are two beneficial effects of G. diazotrophicus on sugarcane growth: one dependent and one not dependent on nitrogen fixation. A plant growth-promoting substance, such as indole-3-acetic acid (IAA), known to be produced by G. diazotrophicus, could be a nitrogen fixation-independent factor. One strain, MAd10, isolated by screening a library of Tn5 mutants, released only 6% of the amount of IAA excreted by the parent strain in liquid culture. The mutation causing the IAA^– phenotype was not linked to Tn5. A pLAFR3 cosmid clone that complemented the IAA deficiency was isolated. Sequence analysis of a complementing subclone indicated the presence of genes involved in cytochrome c biogenesis (ccm, for cytochrome c maturation). The G. diazotrophicus ccm operon was sequenced; the individual ccm gene products were 37 to 52% identical to ccm gene products of Escherichia coli and equivalent cyc genes of Bradyrhizobium japonicum. Although several ccm mutant phenotypes have been described in the literature, there are no reports of ccm gene products being involved in IAA production. Spectral analysis, heme-associated peroxidase activities, and respiratory activities of the cell membranes revealed that the ccm genes of G. diazotrophicus are involved in cytochrome c biogenesis.

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* Corresponding author. Mailing address: Division of Plant Pathology and Microbiology, Department of Plant Sciences, P.O. Box 210036, Forbes 204, University of Arizona, Tucson, AZ 85721. Phone: (520) 621-9835. Fax: (520) 621-9290. E-mail: ckennedy{at}u.arizona.edu.

Present address: Howard Hughes Medical Institute, Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461.

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Journal of Bacteriology, August 2004, p. 5384-5391, Vol. 186, No. 16
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.16.5384-5391.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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