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Applied and Environmental Microbiology, August 2009, p. 5012-5017, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00755-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Aerobic Vanillate Degradation and C1 Compound Metabolism in Bradyrhizobium japonicum{triangledown} ,{dagger}

Nirinya Sudtachat, Naofumi Ito, Manabu Itakura, Sachiko Masuda, Shima Eda, Hisayuki Mitsui, Yasuyuki Kawaharada, and Kiwamu Minamisawa*

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

Received 3 April 2009/ Accepted 27 May 2009

Bradyrhizobium japonicum, a symbiotic nitrogen-fixing soil bacterium, has multiple gene copies for aromatic degradation on the genome and is able to use low concentrations of vanillate, a methoxylated lignin monomer, as an energy source. A transcriptome analysis indicated that one set of vanA1B, pcaG1H1, and genes for C1 compound catabolism was upregulated in B. japonicum USDA110 cells grown in vanillate (N. Ito, M. Itakura, S. Eda, K. Saeki, H. Oomori, T. Yokoyama, T. Kaneko, S. Tabata, T. Ohwada, S. Tajima, T. Uchiumi, E. Masai, M. Tsuda, H. Mitsui, and K. Minamisawa, Microbes Environ. 21:240-250, 2006). To examine the functions of these genes in vanillate degradation, we tested cell growth and substrate consumption in vanA1B, pcaG1H1, and mxaF mutants of USDA110. The vanA1B and pcaG1H1 mutants were unable to grow in minimal media containing 1 mM vanillate and protocatechuate, respectively, although wild-type USDA110 was able to grow in both media, indicating that the upregulated copies of vanA1B and pcaG1H1 are exclusively responsible for vanillate degradation. Mutating mxaF eliminated expression of gfa and flhA, which contribute to glutathione-dependent C1 metabolism. The mxaF mutant had markedly lower cell growth in medium containing vanillate than the wild-type strain. In the presence of protocatechuate, there was no difference in cell growth between the mxaF mutant and the wild-type strain. These results suggest that the C1 pathway genes are required for efficient vanillate catabolism. In addition, wild-type USDA110 oxidized methanol, whereas the mxaF mutant did not, suggesting that the metabolic capability of the C1 pathway in B. japonicum extends to methanol oxidation. The mxaF mutant showed normal nodulation and N2 fixation phenotypes with soybeans, which was not similar to symbiotic phenotypes of methylotrophic rhizobia.

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

{triangledown} Published ahead of print on 5 June 2009.

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

Applied and Environmental Microbiology, August 2009, p. 5012-5017, Vol. 75, No. 15
0099-2240/09/$08.00+0     doi:10.1128/AEM.00755-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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