Refardt, Dominik, Dr.

My research interests - evolution of parasitism

Living at the expense of others is a clever life style which has been adopted by a large part of the living world. At the same time it is puzzling, because the parasite harms the resource it relies on, its host. How does it manage to bite the hand that feeds it and get away with it?

Evolutionarily speaking, parasites constantly adapt to counter-adaptations of their hosts, creating a never ending race between two antagonists. This provides the launchpad for the evolution of sex and recombination, it helps to understand what parasite virulence is and why it can't be avoided and last but not least it underlies the evolution of generally fascinating phenotypes such as highly reduced genomes and complicated life cycles.

Since I entered the biological sciences, I studied causes and consequences of parasitism, first with unicellular parasites of waterfleas, now with acellular parasites of bacteria. If you share my interests, contact me. I am interested in all sorts of interactions, be it a collaboration among peers or the supervision of a masters thesis.

Temperate Bacteriophages

Bacteriophages are viral predators of bacteria. While some of them invariably kill their host after infection (lysis), temperate phages can decide to remain benign: they insert themselves into the genome of their host and remain there quietly as a so called prophage (lysogeny). Such a prophage can be triggered to excise itself again and kill the host, typically via the bacterial SOS response (prophage induction).

Thus, we have here a very simple organism with a dual transmission strategy. Either aggressive (lysis) or benign (lysogeny). How the phage behaves depends on two decisions. One is made after infection (kill now or sit and wait?), the second is made during lysogeny (leave now or stay longer?), and together they define the phage life cycle. How phage behavior works mechanistically is understood in great detail thanks to decades of experimental investigation.

I want to place this knowledge in an ecological and evolutionary framework. What are the advantages of having those two life styles and under what conditions should a phage choose either lysis or lysogeny? Now that the importance of phages in many ecosystems is recognized, we must understand what selective forces shape them and how they respond.

Evolution of microsporidian parasites

Microsporidia a highly specialized unicellular parasites. Possibly because of their parasitic life style (they are intracellular parasites), they have small and compacted genomes and highly reduced mitochondria. In addition to that, they evolve at a high rate. Taken together, they have a rather "protist-like" appearance, which has tricked taxonomists for a long time into believing that they are very ancient eukaryotes.

Now it is fairly certain that they have a fungal origin. Their ancestor was probably a chytrid or zygomycete which adopted a parasitic life-style that subsequently gave rise to thousands of highly specialized species that gained the status of a phylum. Who the ancestor is and where exactly in the fungal tree it is located is not known.

We might have identified a species that could be the missing link between fungi and microsporidia. With the help of Jiri Vavra (Charles University, Praque) and Tim James (University of Michigan) I am currently tightening this up by sequencing more genes of it. In the best of all cases it turns out to be indeed a close relative of the "missing link", if not, well... at least we will have learned at a lot about a very peculiar parasite!

Prospective students

I am currently looking for new students to join my lab. If you are looking for a place to do your masters, I would be delighted if you contacted me to discuss mutual interests and the possible opportunities. I mainly work with phages nowadays, but it doesn't take a lot to spark my interest for microsporidia again.

Publications

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