Pathogen-host reorganization during Chlamydia invasion revealed by cryo-electron tomography

Area of Science:

• Microbiology
• Cell Biology
• Structural Biology

Background:

• Bacterial invasion of host cells is crucial for infection but poorly understood in 3D.
• Chlamydia trachomatis causes significant human diseases like STIs and trachoma.

Purpose of the Study:

• To visualize the three-dimensional structural dynamics of Chlamydia elementary body invasion.
• To elucidate the role of bacterial polarity and secretion systems in host cell entry.

Main Methods:

• Whole-cell cryo-electron tomography of Chlamydia trachomatis LGV2 elementary bodies (EBs).
• In situ imaging of early bacterial endocytosis within host cells.

Main Results:

• Chlamydial EBs are intrinsically polarized, with one pole featuring type III secretion systems (T3SSs).
• EBs orient with the T3SS-containing pole towards host cells, contacting the plasma membrane.
• Host cell entry involves macropinosomes and actin rearrangements, leading to tight vacuole encapsulation.
• Bacterial polarity and T3SSs are lost after internalization.

Conclusions:

• This study reveals novel structural transitions in both Chlamydia and host cells during invasion.
• Polarized orientation and T3SSs are critical for initiating Chlamydia entry into host cells.