Developmental cycle of Coxiella burnetii: structure and morphogenesis of vegetative and sporogenic differentiations

Abstract

Coxiella burnetii is a gram-variable obligate intracellular bacterium which carries out its development cycle in the phagolysosome of eucaryotic cells. Ultrastructural analysis of C. burnetii, 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 (SCV). Potassium permanganate staining of purified rickettsiae revealed a number of differences in the internal structures of the cell variants. (i) The outer membrane of the SCV and LCV were comparable; however, the underlying dense layer of the SCV was much wider and more prominent than that of the LCV. The periplasmic space of the SCV 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 SCV. 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 C. burnetii is comparable, although not identical, to cellular differentiation of endospore formation. A developmental cycle consisting of vegetative and sporogenic differentiation is proposed.

Autophagy induction favours the generation and maturation of the Coxiella-replicative vacuoles

“…With this dilution an MOI of 10 was obtained. C. burnetii number was estimated using Gimenez staining (McCaul and Williams, 1981). Cells were incubated for different periods of time at 37∞C in an atmosphere of 95% air and 5% CO 2 .…”

“…The replication of C. burnetii , in acidic phagolysosomes is a paradigmatic example of a pathogen that survives in a harsh intracellular environment. This resistance is in part attributed to the pathogen's biphasic developmental cycle, with two morphologically, compositionally and functionally distinct forms: the metabolically dormant, less replicating and environmentally stable small cell variants (SCVs) and the metabolically active, replicating and more fragile large cell variants (LCVs) (McCaul and Williams, 1981). SCVs are now thought to be infective forms (Hackstadt, 1996) although a spore-like particle (SLP) has been ultrastructurally described.…”

A Sporulation Gene in Coxiella burnetii?

“…Compared t o other members of the family Rickettsiaceae the organism displays an unusually high resistance against environmental conditions. The existence of "endospored' (MCCAUL and WILLIAMS, 1981) o r "spore-like forms" (SCHAAL et al, 1987;JEKOV, 1985), and "small dense cells" (MCCAUL et al, 1991) has been described and such forms characterized by electron microscopy and immunologically (MCCAUL et al, 1991). As a consequence a complex cycle of differentiation has been postulated (MCCAUL and WIL-Searching for conserved target sequences for a diagnostic PCR to improve the diagnosis of Q fever we have cloned and sequenced a NotIIEcoRV fragment from genomic DNA of C. burnetii, isolate "NINE MILE", phase I.…”

A comparison of methods for extracting DNA from Coxiella burnetii as measured by a duplex qPCR assay

“…The SCV were apparently protected from these effects, as no significant difference was demonstrated with the filtered (SCV only) samples. The SCV of C. burnetii has condensed chromatin (McCaul and Williams 1981), which may prevent inhibitors binding and ⁄ or increase the temperature required to separate the strands of DNA, hence protecting the DNA from inhibitors binding to the separated strands. For the samples spiked with either the unfiltered or filtered cultures, the silica column method (RBC-silica) extracted the largest amounts of detectable DNA.…”