This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The bacterium Chlamydia trachomatis is one of the most common causes of sexually transmitted infections worldwide. Biologically, it is regarded as a highly specialized "nutrient thief": Because chlamydia have lost the ability to reproduce independently outside a host cell, they hijack human metabolic products—particularly sphingolipids—for their own development.
Within the host cell, they create a sheltered environment known as an inclusion. These bacterial colonies often grow so large that they exceed the size of the human host cell's nucleus. The life cycle of these pathogens is characterized by extreme morphological change.
They alternate between robust, infectious elementary bodies during their time outside the cell and active reticular bodies that multiply inside host cells. To protect the genetic material during the infectious phase, the DNA within the tiny elementary bodies is packed extremely tightly into a nucleoid. For a long time, investigating this internal structure posed a challenge for scientists: Measuring just 200 to 300 nanometers in size, the elementary bodies lie below the physical resolution limit of conventional light microscopes.
This even led to chlamydia being mistakenly regarded as viruses until the 1960s. New findings from Würzburg are now unraveling the mystery of this compact architecture. The study, now published in the journal Nature Communications, was carried out by a team led by professor Thomas Rudel, head of the Chair of Microbiology at the University of Würzburg; the co-first authors are Marcel Rühling and Fabienne Wagner.
In their study, the research team demonstrates that not only proteins but also lipids play a crucial role in the organization of the bacterial genome. In particular, the sphingolipid sphingomyelin is incorporated directly into the highly compacted nucleoid. The spatial correlation is striking: Around 90% of the nucleoid in the infectious form is occupied by these lipids.
"To our surprise, in our experiments we observed the highly dynamic incorporation and removal of a sphingomyelin derivative in bacterial nucleoids during the developmental cycle," explains Rudel. This observation was made possible only by a combination of techniques that produces images with unprecedented levels of detail. To overcome the physical limitations of optics, the team used expansion microscopy (ExM).
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