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Journal of Bacteriology, May 2003, p. 3031-3035, Vol. 185, No. 10
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.10.3031-3035.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

S-Adenosylmethionine Transport in Rickettsia prowazekii

Aimee M. Tucker, Herbert H. Winkler, Lonnie O. Driskell, and David O. Wood*

Laboratory of Molecular Biology, Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, Alabama 36688

Received 9 December 2002/ Accepted 28 February 2003

Rickettsia prowazekii, the causative agent of epidemic typhus, is an obligate, intracellular, parasitic bacterium that grows within the cytoplasm of eucaryotic host cells. Rickettsiae exploit this intracellular environment by using transport systems for the compounds available in the host cell's cytoplasm. Analysis of the R. prowazekii Madrid E genome sequence revealed the presence of a mutation in the rickettsial metK gene, the gene encoding the enzyme responsible for the synthesis of S-adenosylmethionine (AdoMet). Since AdoMet is required for rickettsial processes, the apparent inability of this strain to synthesize AdoMet suggested the presence of a rickettsial AdoMet transporter. We have confirmed the presence of an AdoMet transporter in the rickettsiae which, to our knowledge, is the first bacterial AdoMet transporter identified. The influx of AdoMet into rickettsiae was a saturable process with a KT of 2.3 µM. Transport was inhibited by S-adenosylethionine and S-adenosylhomocysteine but not by sinfungin or methionine. Transport was also inhibited by 2,4-dinitrophenol, suggesting an energy-linked transport mechanism, and by N-ethylmaleimide. AdoMet transporters with similar properties were also identified in the Breinl strain of R. prowazekii and in Rickettsia typhi. By screening Escherichia coli clone banks for AdoMet transport, the R. prowazekii gene coding for a transporter, RP076 (sam), was identified. AdoMet transport in E. coli containing the R. prowazekii sam gene exhibited kinetics similar to that seen in rickettsiae. The existence of a rickettsial transporter for AdoMet raises intriguing questions concerning the evolutionary relationship between the synthesis and transport of this essential metabolite.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, Laboratory of Molecular Biology, University of South Alabama, Mobile, AL 36688-0002. Phone: (251) 460-6324. Fax: (251) 460-7269. E-mail: wood{at}sungcg.usouthal.edu.

Journal of Bacteriology, May 2003, p. 3031-3035, Vol. 185, No. 10
0021-9193/03/$08.00+0     DOI: 10.1128/JB.185.10.3031-3035.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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