Developmental cycle of XXXX : structure and morphogenesis of vegetative and sporogenic differentiations.

@entity4003 @entity19592 @entity6723
@entity4003 is a gram-variable obligate intracellular bacterium which carries out its development cycle in the phagolysosome of eucaryotic cells. Ultrastructural analysis of @entity4003 , in situ and after Renografin purification, by transmission electron microscopy of lead-stained thin sections has revealed extreme pleomorphism as demonstrated by two morphological cell types, a large cell variant (LCV) and a small cell variant ( @entity6723 ). @entity19592 staining of purified rickettsiae revealed a number of differences in the internal structures of the cell variants. (i) The outer membrane of the @entity6723 and LCV were comparable; however, the underlying dense layer of the @entity6723 was much wider and more prominent than that of the LCV. The periplasmic space of the @entity6723 was not readily visualized, whereas the periplasmic space of the LCV was apparent and resembled that of other gram-negative bacteria. (ii) Complex internal membranous intrusions which appeared to originate from the cytoplasmic membrane were observed in the @entity6723 . The LCV did not harbor an extensive membranous system. (iii) Some LCVs contained a dense body in the periplasmic space. This endogenous structure appeared to arise in one pole of the LCV as an electrondense "cap" formation with the progressive development of a dense body approximately 130 to 170 nm in diameter which was eventually surrounded by a coat of at least four layers. Our observations suggest that the morphogenesis of @entity4003 is comparable, although not identical, to cellular differentiation of endospore formation. A developmental cycle consisting of vegetative and sporogenic differentiation is proposed.
