Univ.-Prof. Dr. Matthias Horn

Chlamydiae are well-known as important pathogens of humans but have more recently also been found as symbionts of free-living amoebae. Molecular surveys suggest that the chlamydiae are highly diverse, likely infecting almost any animal lineage. They represent one of the evolutionary oldest strictly intracellular groups of microbes, with their last common ancestor having lived around one billion years ago. Studying chlamydial symbionts such as Protochlamydia amoebophila and Parachlamydia acanthamoebae, the comparison with their pathogenic counterparts, as well as evolution experiments using these symbionts allow us to investigate the evolution of the intracellular lifestyle of chlamydiae and their adaptation to different eukaryotic hosts. This research is carried out within the group of Matthias Horn, together with Astrid Collingro.

Recent project: Chlamydial symbionts in dictyostelids
The soil amoeba Dictyostelium discoideum is one of the best-known protist model systems and famous for its so-called social life cycle, a conserved mechanism found in all dictyostelids. During this life cycle, tens of thousands of cells aggregate and develop multicellular structures, eventually leading to the formation of spores. Recent evidence suggests that in nature chlamydial symbionts are widespread among dictyostelids. In this project, we aim to understand the diversity of chlamydial symbionts in dictyostelids and ask how chlamydiae adapted to the specific social life cycle of dictyostelid amoebae.
Collaboration partners:Susanne DiSalvo (Southern Illinois University Edwardsville), Tamara Haselkorn (University of Central Arkansas), Thiery Soldati (University of Geneva).

Many protists harbor specific bacterial symbionts. The function of these symbionts is, however, mostly unknown, and so are the underlying mechanisms of host interactions.

We are using diverse model systems to better understand the role of microbial symbionts for their protist hosts. We have shown that chlamydial symbionts can protect amoeba from lethal infections with the bacterial pathogen Legionella pneumoniae, and we have described an unusual protein secretion system in the amoeba symbiont Amoebophilus asiaticus.

We study amoeba symbionts such as Nucleicultrix amoebiphila to better understand how bacteria target and replicate in the nucleus of their host cells.