New paper in Nature Microbiology: Genome expansion in bacterial endosymbionts

Chlamydiae is known for the infamous human pathogen Chlamydia, but this group of bacteria evolved over a billion years ago. Despite being ancient and diverse, all chlamydiae today are intracellular and depend on living inside the cells of hosts ranging from animals to single-cell amoeba. In a study published in Nature Microbiology a team around Stephan Köstlbacher and Matthias Horn from DoME, and Jennah Dharamshi and Thijs Ettema from Wageningen University & Research reports that the ancestor of Chlamydiae likely already lived inside host cells. But that chlamydiae infecting amoeba later evolved in unexpected ways for intracellular bacteria: Counter to expectations for genome streamlining in strict endosymbionts, using ancestral state reconstruction they detected substantial gene gain within Chlamydiae. In particular, genes involved in energy metabolism and aerobiosis characteristic of the more metabolically versatile protist-infecting chlamydiae were gained. The study shows that metabolic complexity can increase during endosymbiont evolution, adding an additional perspective for understanding symbiont evolutionary trajectories across the tree of life.

From left to right authors Astrid Collingro, Jennah Dharamshi, and Stephan Köstlbacher at the 2022 Planctomycetes, Verrucomicrobia, Chlamydia (PVC) V meeting in Bergen, Norway.