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Journal of Bacteriology, July 2009, p. 4522-4533, Vol. 191, No. 14
0021-9193/09/$08.00+0     doi:10.1128/JB.00272-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

orf4 of the Bacillus cereus sigB Gene Cluster Encodes a General Stress-Inducible Dps-Like Bacterioferritin{triangledown}

Shin-Wei Wang,1 Chien-Yen Chen,2 Joseph T. Tseng,3 Shih-Hsiung Liang,1 Ssu-Ching Chen,1 Chienyan Hsieh,1 Yen-hsu Chen,4 and Chien-Cheng Chen1*

Department of Biotechnology, National Kaohsiung Normal University, 62 Shenjhong Rd., Yanchao Township, Kaohsiung County 82444, Taiwan,1 Department of Earth and Environmental Sciences, National Chung Cheng University, 168 University Road, Min-Hsiung, Chiayi 621, Taiwan,2 Institute of Bioinformatics, College of Bioscience and Biotechnology, National Cheng Kung University, Tainan 70101, Taiwan,3 Division of Infectious Diseases, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan4

Received 2 March 2009/ Accepted 28 April 2009

The function of orf4 in the sigB cluster in Bacillus cereus ATCC 14579 remains to be explored. Amino-acid sequence analysis has revealed that Orf4 is homologous with bacterioferritins and Dps. In this study, we generated an orf4-null mutant and produced recombinant protein rOrf4 to establish the role of orf4. In vitro, the purified rOrf4 was found to exist in two distinct forms, a dimeric form and a polymer form, through size exclusion analysis. The latter form exhibited a unique filament structure, in contrast to the typical spherical tetracosamer structure of bacterioferritins; the former can be induced to form rOrf4 polymers immediately after the addition of FeCl2. Catalysis of the oxidation of ferrous irons by ferroxidase activity was detected with rOrf4, and the mineralized irons were subsequently sequestered only in the rOrf4 polymer. Moreover, rOrf4 exerted DNA-protective activity against oxidative damage via DNA binding in a nonspecific manner, as is seen with Dps. In vivo, deletion of orf4 had no effect on activation of the alternative sigma factor {sigma}B, and therefore, orf4 is not associated with {sigma}B regulation; however, orf4 can be significantly upregulated upon environmental stress but not H2O2 treatment. B. cereus strains with constitutive Orf4 expression exhibited a viability higher than that of the orf4-null mutant, under specific oxidative stress or heat shock. Taken together, these results suggest that Orf4 functions as a Dps-like bacterioferritin in response to environmental stress and can provide cell protection from oxidative damage through iron sequestration and DNA binding.

* Corresponding author. Mailing address: Department of Biotechnology, National Kaohsiung Normal University, 62 Shenjhong Rd., Yanchao Township, Kaohsiung County 82444, Taiwan. Phone: 886-7-7172930. Fax: 886-7-6051353. E-mail: cheng{at}nknu.edu.tw

{triangledown} Published ahead of print on 1 May 2009.

Journal of Bacteriology, July 2009, p. 4522-4533, Vol. 191, No. 14
0021-9193/09/$08.00+0     doi:10.1128/JB.00272-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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