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Journal of Bacteriology, November 2006, p. 7572-7580, Vol. 188, No. 21
0021-9193/06/$08.00+0     doi:10.1128/JB.00576-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The dps Gene of Symbiotic "Candidatus Legionella jeonii" in Amoeba proteus Responds to Hydrogen Peroxide and Phagocytosis

Miey Park,^1, Seong Tae Yun,^1, Sue-Yun Hwang,² Choong-Ill Chun,³ and Tae In Ahn^1*

Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea,¹ Graduate School of Biology and Information Technology, Hankyong National University, 67 Sokjong-Dong, Kyonggi-Do 456-749, Republic of Korea,² Department of Biological Science, Sookmyung Women's University, Seoul 140-742, Republic of Korea³

Received 24 April 2006/ Accepted 16 August 2006

To survive in host cells, intracellular pathogens or symbiotic bacteria require protective mechanisms to overcome the oxidative stress generated by phagocytic activities of the host. By genomic library tagging, we cloned a dps (stands for DNA-binding protein from starved cells) gene of the symbiotic "Candidatus Legionella jeonii" organism (called the X bacterium) (dps_X) that grows in Amoeba proteus. The gene encodes a 17-kDa protein (pI 5.19) with 91% homology to Dps and DNA-binding ferritin-like proteins of other organisms. The cloned gene complemented the dps mutant of Escherichia coli and conferred resistance to hydrogen peroxide. Dps_X proteins purified from E. coli transformed with the dps_X gene were in oligomeric form, formed a complex with pBlueskript SKII DNA, and protected the DNA from DNase I digestion and H₂O₂-mediated damage. The expression of the dps_X gene in "Candidatus Legionella jeonii" was enhanced when the host amoeba was treated with 2 mM H₂O₂ and by phagocytic activities of the host cell. These results suggested that the Dps protein has a function protective of the bacterial DNA and that its gene expression responds to oxidative stress generated by phagocytic activities of the host cell. With regard to the fact that invasion of Legionella sp. into respiratory phagocytic cells causes pneumonia in mammals, further characterization of dps_X expression in the Legionella sp. that multiplies in a protozoan host in the natural environment may provide valuable information toward understanding the protective mechanisms of intracellular pathogens.

Published ahead of print on 1 September 2006.

These authors contributed equally to this work.

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