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Permeability of Coxiella burnetii to ribonucleosides

Department of Microbiology and Immunology, Robert E. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26506, USA¹

Author for correspondence: Herbert A. Thompson. Tel: +1 404 639 1083. Fax: +1 404 639 1056. e-mail: hct2{at}cdc.gov

Knowledge about transport in Coxiella burnetii, an obligate phagolysosomal parasite, is incomplete. The authors investigated the capability of isolated, intact, host-free Coxiella to transport ribonucleosides while incubated at a pH value typical of lysosomes. Because of the low activities and limitations of obtaining experimental quantities of isolated, purified Coxiella, incorporation of substrate into nucleic acid was used as a trap for determination of uptake abilities. Virulent wild-type (phase I) organisms possessed uptake capability for all ribonucleosides. Both phase I and phase II (avirulent) organisms incorporated the purine nucleosides guanosine, adenosine and inosine, and showed a more limited uptake of thymidine and uridine. Both phases were poorly active in cytidine uptake. Neither phase of the organism was capable of transport and incorporation of NTPs, CMP, cytosine or uracil. Water space experiments confirmed that the uptake process concentrated the purine nucleosides within the cytoplasm of both wild-type and phase II Coxiella via a low-pH-dependent mechanism. Comparison of uptake rates in Escherichia coli versus Coxiella verified that the incorporation of ribonucleosides by Coxiella is a slow process. It is concluded that Coxiella possesses some transport pathways consistent with utilization of pools of nucleosides found within its host cell lysosomal pathway.

Keywords: nucleosides and nucleotides, phase I and phase II activity, cell volume, growth in chick embryos

Abbreviations: CCCP, carbonyl cyanide m-chlorophenylhydrazine

^a Present address: Q Fever Unit, Rickettsial Section, Viral and Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30333, USA.

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