Morphological remodeling of Coxiella burnetii during its biphasic developmental cycle revealed by cryo-electron tomography

Doulin C Shepherd; Mohammed Kaplan; Naveen Vankadari; Ki Woo Kim; Charles L Larson; Przemysław Dutka; Paul A Beare; Edward Krzymowski; Robert A Heinzen; Grant J Jensen; Debnath Ghosal

doi:10.1016/j.isci.2023.107210

Morphological remodeling of Coxiella burnetii during its biphasic developmental cycle revealed by cryo-electron tomography

iScience. 2023 Jun 24;26(7):107210. doi: 10.1016/j.isci.2023.107210. eCollection 2023 Jul 21.

Authors

Doulin C Shepherd¹, Mohammed Kaplan², Naveen Vankadari¹, Ki Woo Kim^{2

3}, Charles L Larson⁴, Przemysław Dutka^{2

5}, Paul A Beare⁴, Edward Krzymowski⁶, Robert A Heinzen⁴, Grant J Jensen^{2

7}, Debnath Ghosal^{1

8}

Affiliations

¹ Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia.
² Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
³ School of Ecology and Environmental System, Kyungpook National University, Sangju, Korea.
⁴ Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA.
⁵ Division od Chemistry and Chemical Engineering, California Institute of Technology, 1200 California Boulevard, Pasadena, CA 91125, USA.
⁶ Department of Physics and Astronomy, Brigham Young University, Provo, UT 84604, USA.
⁷ Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84604, USA.
⁸ ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia.

Abstract

Coxiella burnetii is an obligate zoonotic bacterium that targets macrophages causing a disease called Q fever. It has a biphasic developmental life cycle where the extracellular and metabolically inactive small cell variant (SCV) transforms inside the host into the vegetative large cell variant (LCV). However, details about the morphological and structural changes of this transition are still lacking. Here, we used cryo-electron tomography to image both SCV and LCV variants grown either under axenic conditions or purified directly from host cells. We show that SCVs are characterized by equidistant stacks of inner membrane that presumably facilitate the transition to LCV, a transition coupled with the expression of the Dot/Icm type IVB secretion system (T4BSS). A class of T4BSS particles were associated with extracellular densities possibly involved in host infection. Also, SCVs contained spherical multilayered membrane structures of different sizes and locations suggesting no connection to sporulation as once assumed.

Keywords: Microbiology; Structural biology.