Conjugative plasmid pLD-TEX-KL promotes growth of host bacterium Legionella dumoffii at low temperatures
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Legionella (Fluoribacter) dumoffii is a resident of various aquatic environments and occasionally causes pneumonia in humans. We found that L. dumoffii strain TEX-KL carries a 66-kb circular plasmid. As predicted by the presence of tra genes similar to those of other transferable plasmids, we showed that pLD-TEX-KL was actually capable of transferring itself to a plasmid-cured derivative of the original strain. Unexpectedly, this plasmid-free derivative turned out to be partially defective in terms of growth at temperatures 30°C or lower. Subsequent works revealed that the growth defect was attributable to the loss of the plasmid gene traA(Ti) homologous to the traA gene of Ti plasmid from Agrobacterium tumefaciens, and that the growth was restored by the introduction of the mobA/repB gene of plasmid pMMB207. Since the existence of a DNA nickase domain is the only feature common to the traA(Ti) and mobA/repB gene products, we hypothesized that this growth defect at low temperature is related to insufficient DNA transactions, which can somehow be alleviated by the nickase activity of those plasmid-encoded proteins. It was also noted that the above features of growth defect at low temperatures were seen in L. dumoffii cells parasitizing the amebic host Acanthamoeba culbertsoni.
KeywordsLegionella dumoffii pLD-TEX-KL Conjugative transfer Low temperature TraA
We thank Hideko Kajiwara for technical assistance and Sharon Y. A. M. Villanueva for comments on the manuscript. We also thank Takayoshi Yamaguchi and Eiji Harada for useful suggestions. This work was supported by grant 14370094 from the Ministry of Education, Science, Culture and Sports of Japan and grant H14-047 from the Ministry of Health, Labor and Welfare of Japan.
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