Chlamydia bacteria collects DNA from the inside out

Published on
January 10, 2023

Family members of the chlamydia-causing bacteria collect genes inside their host to enrich their DNA. These new genes help them survive outside their host. That is especially useful for chlamydia bacteria infecting microscopically small amoeba, which regularly switch hosts. Therefore, they collect more DNA than their cousins infecting multicellular hosts, including humans. This was discovered by an international team of scientists of Wageningen, Uppsala and Vienna.

The researchers used state-of-the-art computational methods to model the path of evolution from chlamydial ancestors to species found today. They concluded that the ancestor likely already lived inside host cells. Later, family members infecting amoeba added metabolic genes to their genome to help gain energy and cope with higher levels of oxygen, which can be toxic to some microorganisms.

Horizontal gene transfer

That bacteria exchange genetic material is not new. This so-called horizontal gene transfer helps them to acquire new traits and adapt to changing environments. However, bacteria living inside a host (endosymbionts) lead relatively isolated lives and have few opportunities to exchange genes. Yet, they do encounter other bacteria inside the host: amoeba often host multiple endosymbionts and they eat bacteria, so there are other microbes around to exchange genes with. “Most Chlamydiae move between different hosts and get exposed to changing environments, which could explain why there is selection to keep and even gain metabolic genes,” says Matthias Horn, co-senior author and Professor at the University of Vienna.

Sequencing environmental samples

Why haven’t researchers uncovered these results earlier? “Most life on earth is microbial, but many microbes are extremely difficult to grow in the lab” clarifies Thijs Ettema, co-senior author and professor at Wageningen University & Research. “We have only recently gained the capability to sequence genomes directly from environmental samples and explore the breadth of chlamydial diversity”.

The teams of Ettema and Horn had independently discovered new Chlamydiae genomes in environments ranging from the deep sea to sponges to Antarctic lakes. They decided to team up and use the new data to reconstruct how Chlamydiae evolved. “While we focused on one ancient group of endosymbionts, the Chlamydiae, we are confident this mode of endosymbiont evolution is more widespread”, say Jennah Dharamshi (Uppsala University) and Stephan Köstlbacher (University of Vienna and Wageningen University & Research), the two co-first authors of the study. The research is an important step for understanding the emergence and evolution of endosymbiotic bacteria, including human pathogens.


Dharamshi, J.E., Köstlbacher, S., Schön, M.E. et al. Gene
gain facilitated endosymbiotic evolution of Chlamydiae. Nat Microbiol 8,
40–54 (2023).

In addition to Thijs J. G. Ettema, Matthias Horn, Jennah Dharamshi, and Stephan Köstlbacher, study authors also include , Max E. Schön (Uppsala University) and Astrid Collingro (University of Vienna).