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Applied and Environmental Microbiology, August 2009, p. 5037-5046, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00398-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Comparative Genome-Wide Transcriptional Profiling of Azorhizobium caulinodans ORS571 Grown under Free-Living and Symbiotic Conditions {triangledown} ,{dagger}

Shuhei Tsukada,{ddagger} Toshihiro Aono,{ddagger}* Noriko Akiba, Kyung-Bum Lee,§ Chi-Te Liu, Hiroki Toyazaki, and Hiroshi Oyaizu

Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan

Received 17 February 2009/ Accepted 8 June 2009

The whole-genome sequence of the endosymbiotic bacterium Azorhizobium caulinodans ORS571, which forms nitrogen-fixing nodules on the stems and roots of Sesbania rostrata, was recently determined. The sizes of the genome and symbiosis island are 5.4 Mb and 86.7 kb, respectively, and these sizes are the smallest among the sequenced rhizobia. In the present study, a whole-genome microarray of A. caulinodans was constructed, and transcriptomic analyses were performed on free-living cells grown in rich and minimal media and in bacteroids isolated from stem nodules. Transcriptional profiling showed that the genes involved in sulfur uptake and metabolism, acetone metabolism, and the biosynthesis of exopolysaccharide were highly expressed in bacteroids compared to the expression levels in free-living cells. Some mutants having Tn5 transposons within these genes with increased expression were obtained as nodule-deficient mutants in our previous study. A transcriptomic analysis was also performed on free-living cells grown in minimal medium supplemented with a flavonoid, naringenin, which is one of the most efficient inducers of A. caulinodans nod genes. Only 18 genes exhibited increased expression by the addition of naringenin, suggesting that the regulatory mechanism responding to the flavonoid could be simple in A. caulinodans. The combination of our genome-wide transcriptional profiling and our previous genome-wide mutagenesis study has revealed new aspects of nodule formation and maintenance.

* Corresponding author. Mailing address: Biotechnology Research Center, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan. Phone: 81 3 5841 2409. Fax: 81 3 5841 2408. E-mail: uaono{at}mail.ecc.u-tokyo.ac.jp

{triangledown} Published ahead of print on 19 June 2009.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

{ddagger} These authors contributed equally to the work.

§ Present address: Center for Information Biology and DNA Data Bank of Japan, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411-8540, Japan.

Present address: Institute of Biotechnology, National Taiwan University, R412, No. 81, Chang-Xing St., Taipei 106, Taiwan (R.O.C.).

Applied and Environmental Microbiology, August 2009, p. 5037-5046, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00398-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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