On the Nature of Obligate Intracellular Symbiosis of Rickettsiae -- Rickettsia prowazekii Cells Import Mitochondrial Porin

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V. V. Emelyanov^1* and M. Yu. Vyssokikh²

¹Gamaleya Institute of Epidemiology and Microbiology, Russian Academy of Medical Sciences, ul. Gamalei 18, 123098 Moscow, Russia; fax: (495) 193-6183; E-mail: vvemilio@mail.ru

²Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia

^* To whom correspondence should be addressed.

Received September 12, 2005; Revision received February 13, 2006

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Mitochondrial porin was identified in Rickettsia prowazekii by Western blot analysis of whole cells and membrane fractions with monoclonal antibody against porin VDAC 1 of animal mitochondria. Using the BLAST server, no protein sequences homologous to mitochondrial porin were found among the rickettsial genomes. Rickettsiae also do not contain their own porin. The protein imported by rickettsiae is weakly extracted by nonionic detergents and, like porin in mitochondria, is insensitive to proteinase K in whole cells. Immunocytochemical analysis showed that it localizes to the outer membrane of the bacterial cells. These data support an earlier suggestion about import by rickettsiae of indispensable proteins from cytoplasm of the host cell as a molecular basis of obligate intracellular parasitism. They are also consistent with the hypothesis invoking a transfer of genes specifying surface proteins from the last common ancestor of rickettsiae and mitochondria to the host genome, and preservation by rickettsiae of the primitive ability to import these proteins.

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KEY WORDS: Rickettsia prowazekii, mitochondria, rickettsia-like endosymbiont, common ancestor, protein import, porin, nature of endocellular symbiosis

DOI: 10.1134/S0006297906070054

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