DOME

Univ.-Prof. Dr. Matthias Horn

Professor at the Division of Microbial Ecology

☎ +43 1 4277 91208
✉ matthias.horn(at)univie.ac.at


» CV
» Researcher profile at the University of Vienna (u:cris)
» Lectures and courses (u:find)

CeMESS/Ludwig Schedl

Our research focuses on bacteria infecting and residing within eukaryotic cells. Using an array of molecular and computational methods, we discover novel intracellular microbes and decipher the molecular mechanisms and evolutionary processes underlying these associations.
Bacteria living within eukaryotic host cells comprise important pathogens as well as symbionts of humans, animals, and protists. Yet, intracellular microbes have long been underestimated with respect to their diversity, distribution in nature, and their ecological importance.
To address this knowledge gap, we investigate selected non-model organisms, including symbionts of amoeba, arthropods, and cnidarians, as well as viruses infecting protists. Current studies include the search for novel giant viruses, the effects of co-infections with multiple intracellular microbes, genome evolution under the constraints of the intracellular life style, and evolution experiments to better understand the evolution of microbe-host interactions.

Research Topics

Evolution and biology of strictly intracellular microbes

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).

Giant viruses: Evolution, adaptation and population dynamics

Viruses are the most abundant biological entities infecting all cellular life forms with major consequences for their individual hosts and entire ecosystems. Yet, they are also the most unknown biological players, with the protist-infecting nucleocytoplasmic large DNA viruses (Nucleocytoviricota), also referred to as giant viruses, as one of the more recent discoveries that challenged our perception of the viral world.
Giant viruses are as large as bacteria both in terms of particle and genome size, and share a number of features previously observed in cellular microorganisms only. Our current knowledge about these unusual viruses is predominantly based on few isolates obtained with a very limited number of protist host species, while metagenomic data suggests a tremendous diversity of yet undiscovered viruses infecting microbial eukaryotes.
We participated in the discovery of the Klosneuvirinae, a group of giant viruses with a record-holding large number of translation-related genes. More recently, we have shown how bacterial symbionts help amoeba hosts to counter infections by giant viruses, representing one of the very few giant virus defense mechanisms in protists.

Stefan Pommer - photopic.at CC BY-NC-SA 4.0

Microbe-host interactions in protists

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.

Bacterial symbionts in arthropods

Arthropods and their bacterial symbionts represent well-known models for studying microbial symbiosis and the interaction between microbes and animal. In our lab, we are particularly interested in the less well studied microbial symbionts and arthropod groups and have investigated bacterial symbionts in the wood louse Porcellio scaber, the dwarf spider Oedothorax gibbosus, mealybugs, and adelgids of the Adelges laricis/Adelges tardus species complex. This research is carried out in parts in collaboration with Alejandro Manzano Marín.

Group Members

Dr. Astrid Collingro

Senior Scientist

Dr. Nisha Goyal

Postdoc

Dr. Sofia Rigou

Postdoc

Dr. Florian Pichlmüller

Technician

Berna de Vries

PhD Student

Panagiota Folla

PhD Student

Lukas Helmlinger

PhD Student

Nick Hofmann

Master's Student

Vitalii Kovtunyk

PhD Student

Florian Panhölzl

PhD Student

Angelika Schwarzhans

PhD Student

Anjana Accamma Chatlanda Biddappa

Master's Student

Publications

Fritsche TR, Horn M, Seyedirashti S, Gautom RK, Schleifer KH, Wagner M. In situ detection of novel bacterial endosymbionts of Acanthamoeba spp. phylogenetically related to members of the Rickettsiales. Applied and Environmental Microbiology. 1999.

Horn M, Fritsche TR, Gautom RK, Schleifer KH, Wagner M. Novel Bacterial Endosymbionts of Acanthamoeba isolates related to the Paramecium Symbiont Caedibacter caryophilus. Environmental Microbiology. 1999.

141 - 142 out of 142

Microbiomes Drive Planetary Health

Matthias Horn is part of the FWF-funded Cluster of Excellence (CoE)

Learn more