Kinematics of Intracellular Chlamydiae Provide Evidence for Contact-Dependent Development

Abstract

A crucial process of chlamydial development involves differentiation of the replicative reticulate body (RB) into the infectious elementary body (EB). We present experimental evidence to provide support for a contactdependent hypothesis for explaining the trigger involved in differentiation. We recorded live-imaging of Chlamydia trachomatis-infected McCoy cells at key times during development and tracked the temporospatial trajectories of individual chlamydial particles. We found that movement of the particles is related to development. Early to mid-developmental stages involved slight wobbling of RBs. The average speed of particles increased sharply at 24 h postinfection (after the estimated onset of RB to EB differentiation). We also investigated a penicillin-supplemented culture containing EBs, RBs, and aberrantly enlarged, stressed chlamydiae. Near-immobile enlarged particles are consistent with their continued tethering to the chlamydial inclusion membrane (CIM). We found a significantly negative, nonlinear association between speed and size/type of particles, providing further support for the hypothesis that particles become untethered near the onset of RB to EB differentiation. This study establishes the relationship between the motion properties of the chlamydiae and developmental stages, whereby wobbling RBs gradually lose contact with the CIM, and RB detachment from the CIM is coincidental with the onset of late differentiation.

Extrusions are phagocytosed and promoteChlamydiasurvival within macrophages

“…We postulated that one mechanistic basis for how extrusions could preserve Chlamydia infectivity is by facilitating continued RB–EB conversion, even while these bacteria are no longer host cell‐associated. The conversion of Chlamydia reticulate bodies (RB) to infectious EB requires bacteria to be within an inclusion and host cell, which may be due to contact of the RB with the inclusion membrane (Wilson, Timms, McElwain, & Bavoil, ; Wilson, Whittum‐Hudson, Timms, & Bavoil, ), and therefore would not be expected to occur for Chlamydia released by lysis of the host cell.…”

“…The conversion of Chlamydia reticulate bodies (RB) to infectious EB requires bacteria to be within an inclusion and host cell, which may be due to contact of the RB with the inclusion membrane (Wilson, Timms, McElwain, & Bavoil, 2006;Wilson, Whittum-Hudson, Timms, & Bavoil, 2009), and therefore would not be expected to occur for Chlamydia released by lysis of the host cell.…”

The Chlamydial Type III Secretion Mechanism: Revealing Cracks in a Tough Nut

“…The environmental cues that result in this event remain undefined, but Wilson et al (2009) have suggested that something as simple as space constraints within the inclusion dictate dissociation. Electron micrographs from multiple groups (Matsumoto, 1982a; Nichols et al, 1985) contain images of cylindrical surface projections emanating from RBs and forming direct connection with the inclusion membrane.…”

Transformation of a plasmid-free, genital tract isolate ofChlamydia trachomatiswith a plasmid vector carrying a deletion in CDS6 revealed that this gene regulates inclusion phenotype

“…A simple explanation of the ‘black hole’ inclusion morphology could be that the growth rate of the CDS6 knockout mutant(s) is reduced at the mid stage of the developmental cycle, generating a distinctive inclusion whose membrane grows normally and would yield doughnut‐shaped inclusions with replicating RBs at the periphery. This is consistent with the contact‐dependent development model of intracellular development (Wilson et al ., , ; Peters et al ., ). It is possible that the protein encoded by CDS6 is also the factor responsible for conferring the virulence properties associated with the C. trachomatis plasmid.…”