Microtubule- and dynein-mediated movement of Orientia tsutsugamushi to themicrotubule organizing center

The host cell microfilaments and microtubules (MTs) are known to play a cri tical role in the life cycles of several pathogenic intracellular microbes by providing for successful invasion and promoting movement of the pathogen once inside the host cell cytoplasm. Orientia tsutsugamushi, an obligate i ntracellular bacterium, enters host cells by induced phagocytosis, escapes to the cytosol, and then replicates in the cytosol. ECV304 cells infected w ith O. tsutsugamushi revealed the colocalization of the MT organizing cente r (MTOC) and cytosolic orientiae by indirect immunofluorescence assay. Usin g immunofluorescence microscopy in the presence and absence of MT-depolymer izing agents (colchicine and nocodazole), it was shown that the cytosolic o riential movement was mediated by MTs. By transfection study (overexpressio n of dynamitin [also called p50], which is known to associate with dynein-d ependent movement), the movement of O. tsutsugamushi to the MTOC was also m ediated by dynein, the minus-end-directed MT-related motor. Although the si gnificance of this movement in the life cycle of O. tsutsugamushi was not p roven, we propose that the cytosolic O. tsutsugamushi bacteria use MTs and dyneins to propel themselves from the cell periphery to the MTOC.