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.

中文翻译：

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重新审视衣原体代谢：种间代谢变异和发育阶段特异性生理活动。

衣原体是一组专性细胞内细菌，包括重要的人类和动物病原体以及无处不在的原生生物的共生体。它们的特点是发育周期，包括两个主要的形态和生理不同的阶段，即复制的网状体和传染性的非分裂基本体。在这篇综述中，我们重建了导致我们目前对衣原体生理学认识的研究历史，重点关注它们的能量和中心碳代谢。然后，我们比较了致病性和环境衣原体的代谢能力，突出了代谢更灵活的环境菌株之间的种间变异性。我们讨论了最近的发现，表明衣原体在整个发育周期中可能不会作为能量寄生虫生活，并且基本体不是代谢惰性的，而是在适当的无菌条件下表现出代谢活性。观察到的基本体的无宿主代谢活动可能反映了对细胞内环境的充分概括，但有证据表明这种活动在生物学上是相关的，并且是细胞外存活和维持感染性所必需的。最近的发现要求重新考虑衣原体代谢和未来的深入分析，以更好地了解衣原体生理学的物种和阶段特异性差异如何影响毒力、组织嗜性和宿主适应。