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
Affiliations
Doulin C. Shepherd
Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia
Mohammed Kaplan
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; Corresponding author
Naveen Vankadari
Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia
Ki Woo Kim
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; School of Ecology and Environmental System, Kyungpook National University, Sangju, Korea
Charles L. Larson
Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
Przemysław Dutka
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; Division od Chemistry and Chemical Engineering, California Institute of Technology, 1200 California Boulevard, Pasadena, CA 91125, USA
Paul A. Beare
Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
Edward Krzymowski
Department of Physics and Astronomy, Brigham Young University, Provo, UT 84604, USA
Robert A. Heinzen
Coxiella Pathogenesis Section, Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT, USA
Grant J. Jensen
Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA; Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84604, USA; Corresponding author
Debnath Ghosal
Department of Biochemistry and Pharmacology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Melbourne, VIC, Australia; ARC Centre for Cryo-electron Microscopy of Membrane Proteins, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VIC, Australia; Corresponding author
Summary: 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.
