Chlamydial metabolism revisited: interspecies metabolic variability and developmental stage-specific physiologic activities

Authors

  • Anders Omsland,

    1. Host-Parasite Interactions Section, Laboratory of Intracellular Parasites, NIAID, NIH, Hamilton, MT, USA
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    • These authors contributed equally.
  • Barbara Susanne Sixt,

    1. Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria
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    • These authors contributed equally.
  • Matthias Horn,

    Corresponding author
    1. Division of Microbial Ecology, Department of Microbiology and Ecosystem Science, University of Vienna, Vienna, Austria
    • Correspondence: Matthias Horn, Department of Microbiology and Ecosystem Science, University of Vienna, A-1090 Vienna, Austria. Tel.: +43 1 4277 76608; e-mail: horn@microbial-ecology.net

      and

      Ted Hackstadt, NIAID, NIH, Hamilton, MT 59840, USA. Tel.: +1 406 363 9308; e-mail: ted_hackstadt@nih.gov

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  • Ted Hackstadt

    Corresponding author
    1. Host-Parasite Interactions Section, Laboratory of Intracellular Parasites, NIAID, NIH, Hamilton, MT, USA
    • Correspondence: Matthias Horn, Department of Microbiology and Ecosystem Science, University of Vienna, A-1090 Vienna, Austria. Tel.: +43 1 4277 76608; e-mail: horn@microbial-ecology.net

      and

      Ted Hackstadt, NIAID, NIH, Hamilton, MT 59840, USA. Tel.: +1 406 363 9308; e-mail: ted_hackstadt@nih.gov

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Abstract

Chlamydiae are a group of obligate intracellular bacteria comprising important human and animal pathogens as well as symbionts of ubiquitous protists. They are characterized by a developmental cycle including two main morphologically and physiologically distinct stages, the replicating reticulate body and the infectious nondividing elementary body. In this review, we reconstruct the history of studies that have led to our current perception of chlamydial physiology, focusing on their energy and central carbon metabolism. We then compare the metabolic capabilities of pathogenic and environmental chlamydiae highlighting interspecies variability among the metabolically more flexible environmental strains. We discuss recent findings suggesting that chlamydiae may not live as energy parasites throughout the developmental cycle and that elementary bodies are not metabolically inert but exhibit metabolic activity under appropriate axenic conditions. The observed host-free metabolic activity of elementary bodies may reflect adequate recapitulation of the intracellular environment, but there is evidence that this activity is biologically relevant and required for extracellular survival and maintenance of infectivity. The recent discoveries call for a reconsideration of chlamydial metabolism and future in-depth analyses to better understand how species- and stage-specific differences in chlamydial physiology may affect virulence, tissue tropism, and host adaptation.

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