Dr. Katherina Psathakis' world is that of microscopes, or more precisely, that of electron microscopes. At the heart of CellNanOS, she makes sure that the tiniest cell structures, some of which are only nanometers in size, are visible. For her, this is always a fascinating sight.

You are responsible for the electron microscopy in CellNanOs. When did you start working at the Osnabrück University?

I studied in Osnabrück myself, that was really a great time. But I performed the practical part of my studies on Crete, where I also wrote my diploma thesis. Afterwards I went to Münster and did my doctorate with a topic in cell biology, although I had previously completed my diploma thesis in marine zoology and marine ecology. Originally, I had also wanted to do a doctorate in this subject area. But it happened that I switched subjects. Doing so, I was involved with electron microscopy during my whole career. After my PhD, I continued working for more than 10 years at the Max Planck Institute for Molecular Biomedicine in Münster in stem cell research, but then I headed back to my home university in Osnabrück because there was a very interesting position in electron microscopy at CellNanOs available (editor's note: Center for Cellular Nanoanalytics Osnabrück).

© Osnabrück University | Lena Dehnen

After all, where else is there such a concentrated form of this possibility to work independently on such large-scale equipment? That's unique and you have to emphasize this location as something special [...].

So you got to know electron microscopy as a method during your studies. Can one say that you gradually fell more and more in love with this microscopy technique?

That's true. It is a very special technique. Back then, people did a lot of cell biology and molecular biology of course, whereas electron microscopy was used comparatively less often  - there were not so many instruments at this - now it is the opposite, now electron microscopy is a complete hype. By always occupying this technical niche, I had the chance to get this great job in the CellNanOs.

What is your main task here in the CellNanOs?

When I arrived here, the CellNanOs was still under construction (editor's note: opening of CellNanOs took place in 2017), i.e. the premises were already planned, but some structural adjustments had to be made to the highly specialized electron microscopes. The appropriate electron microscopes and preparation equipment had to be selected and ordered. So at the beginning, I spent a lot of time on doing so. It's not just pipettes, but large equipment that cost a lot of money. Such devices are always looked at personally and tested with samples that you bring along. Before ordering, we travelled a lot for inquiring and testing similar microscopes elsewhere to make the best choice for our equipment, we even went to London to visit a colleague at Kings College. Afterwards, the devices had to be installed and put into operation. Now, my main task is to make sure that the devices do what they are supposed to do and that people, including students, use the devices for their projects. After all, where else is there such a concentrated form of this possibility to work independently on such large-scale equipment? That's unique and you have to emphasize this location as something special, that's very important. In such a concentrated form as here - we have 7 electron microscopes, all of which can do something different, and in addition you can combine them with our high-resolution light microscopes, that is a beacon throughout Germany, something very special!

What is the most unique electron microscope here at CellNanOs for you?

The scanning electron microscope is very special, it is combined with a microtome (editor's note: a microtome cuts the sample block into wafer-thin, microscopable slices before an image can be taken, a process that originally preceded the image aquisition at the microscope), or the Serial Block Face Imaging method, where you can image very high-volume samples like whole pieces of tissue for instance, at a high resolution in 3 D. For this purpose, the ultramicrotome cuts thin sections of up to 15 nanometers from the sample with a diamond knife and the microscope then creates an image of the cut surface. This happens several thousand times in the microscope. If the many sections are superimposed on each other, a 3D image of the sample is obtained. We have a total of four transmission electron microscopes that produce a two-dimensional image, but the trend is to go into the third dimension and realize it in a high volume. And here we can do both: 3D microscopy in high resolution and 3D microscopy in large volume, and we can do it automatically. That is really great.

© Osnabrück University | Lena Dehnen

Dr. Katherina Psathakis heart beats for electron microscopy. At the CellNanOs, the Center for Cellular Nanoanalytics, she makes sure that the powerful microscopes work properly and she helps and consults scientists to get their dream image. Here, she discusses the results with PhD students Leo and Rico (from left to right).

What kind of projects do you supervise and help with at the CellNanOs?

The projects come from the research groups of our biology department and from external cooperation partners from other universities and research institutions. Of course, the electron microscopy is correspondingly demanding, because no sample is like the other. You have to do a lot of preparation of the sample, you can't just turn on the machine and everything works, every sample is different. It makes a difference whether you want to examine a fruit fly or individual cells, or tissue, or bacteria or yeasts. At the moment, there are projects from the Zoology-Developmental Biology Lab, where you work with fruit flies, from the Microbiology, there you have bacteria or Salmonella, which have infected other cells. We have yeasts, plants... all kinds of samples.

What is your specific task in these projects?

There are doctoral candidates or students who want to learn a lot themselves, so they are taught how to prepare and microscope their samples. But some of them just need a result, i.e. they bring their samples and we prepare everything and do the electron microscopic work for them so that they get handed the finished image only. But of course we also give advice and evaluate the material. Another possibility is that people are trained by me so that they do a practical course in electron microscopy or spend part of their doctoral thesis learning this method. Later on, this gives them the opportunity to apply for appropriate positions with this expertise. This is an expertise that not everyone has and not all universities can offer. This is something special that students here in Osnabrück can learn compared to other universities.

Are there any samples that interest you in particular or that you find visually appealing?

Since I have worked in stem cell biology in Münster for a long time, I still find it fascinating that one can differentiate one cell type to other cell types or even small organs, so-called organoids like miniature-brains, just by reprogramming them. In the case of the brain organoids, you can really see the synapses under the microscope. If you imagine that this has differentiated from a skin cell, I find that very fascinating. I love that I can really see a change in structure under the microscope and not just look at a band in the gel after a PCR. These are really neurons, bacteria or a fly's heart or whatever structure you are looking at and you can witness it with your own eyes. I love to see this diversity and especially the different biological structures. And with every sample you almost always have beautiful structures to find. And time is always running out at the electron microscope. When you sit at the microscope and you have such beautiful samples, the hours pass by and you don't notice it. I often lose myself in this beauty, so I always have to watch my time.

© Osnabrück University | Lena Dehnen

When you sit at the microscope and you have such beautiful samples, the hours pass by and you don't notice it.

Which is your favorite microscope at the CellNanOs? Which technology do you particularly like?

Purely from what you get as a result, the "serial block-face" electron microscope I mentioned before is awesome, of course. Although all you have to do is to insert the prepared sample and come get the results a week later. So it's the result which is rather exciting. The microscope itself is special because it has a microtome inside. To combine it with this high-precision electron microscope is very fascinating. You don't sit at it all the time, but you can watch it again and again throughout the week during image aquisition and start scrolling to the emerging 3D model and get a first impression. That's really great. One run we had once consisted of 3000 single pictures. For the following analysis you need powerful computers, of course. One or two terrabytes of data may come out after a run.
As a technique, I think the immuno-labelling technique is great (editor's note: the antibody labelling of a specific molecule or protein on an ultra-thin microscopic section for exact localisation), even if it is often challenging. Until you get a correct result, until you can say, for example, that the antigen (editor's note: the protein to be labeled) is located on the inner membrane side of an organelle or on the outer one, it is very demanding. Many factors come into play here: The preparative and biochemical side like the choice of antibodies and more. But the best thing for me, almost a hobby, is scanning electron microscopy, the pictures look so great, you could hang them on the wall as art (Dr. Psathaki points to some scanning electron pictures hanging on the walls of her office).

Are you currently giving lectures? Where can students get to know you?

Not yet this semester, but we are planning a course for the coming winter semester (editor's note: winter semester 20/21). It will be about light and electron microscopy, but also about data management. It will be an independent module with a two-week internship. If that works, I would like to offer more myself. If you do your bachelor's degree here, you can of course come to me at any time and do some sort of a small practical course. And, of course, we also train Master's or PhD students if they are interested.

You told me that you worked on your diploma thesis on Crete. What is your connection to Greece?

I'm half-Greek, I'm from Crete and I would have liked to stay there after my diploma, I wanted to continue my studies in marine biology and zoology, but the path took me somewhere else. And I have to say, maybe it was the right way. But Crete is still my home at heart and besides, Greece is my dream country, I like to be there.

What do you do to clear your head?

Actually I wanted to become an outdoor biologist, that's what got me into studying biology. I am an outdoor person: all the outdoors, all day, and of course animals: I own a horse and I go out for a ride with her every evening, so I have enough distraction. Then I like to go running, riding my racing bike, I generally enjoy doing endurance sports, mostly when they take place outside! What I do not like so much are large crowds of people. Some people like going to festivals, I don't have the need to visit a crowded pub in the evening. I rather need fresh air, nature and freedom.


Thanks for the interview!