Zaubern mit Mikroben

Katja Bühler still raves about the view from the roof: It's been a while since she first stood above the campus of the Helmholtz Centre for Environmental Research - UFZ. "You have to be free of giddiness," she says with a grin, "but in return you can look out over the whole of Leipzig!" For the microbiologist, however, the research roof is interesting above all because of her latest project: she soon wants to install a small experimental reactor up here, in which microbes become hydrogen producers.

The allure of microbiology

Working magic with microbes has been Katja Bühler's goal since the beginning of her career. "When I came to university fresh out of school, I was mainly attracted to zoology," the 47-year-old recalls in retrospect - "but then I realized what fascinating worlds you can dive into in microbiology." That was in the 1990s, Bühler was studying at the university in her hometown of Hamburg, and she intuitively grasped that a lot of new things were happening in the field of microbes. "Microbes can always do anything," is how she sums up this appeal: Even in the most inhospitable environments, they settle in. And that's exactly what her research is now based on in Leipzig; she works with so-called biofilms - those thin, slippery layers that form on stagnant water or other surfaces, for example. "They are often resistant to antibiotics and other biocides, which is why they are generally unpopular," says Katja Bühler: "But we want to take advantage of their problematic properties."

You can think of the process as being like a factory, she says, and you can sense that this is not the first time she has explained her complex research: the enzymes in the biofilm take on the role of machines that produce hydrogen. And like real machines, they need energy for this, which they obtain from solar energy - a classic biocatalysis process. There is a system to the fact that Katja Bühler uses biofilm for this process, and not just individual bacteria found in the film: "When bacteria grow as biofilm, various physiological parameters change," she explains: "As a result, they are much more robust in dealing with environmental stress. This improves process stability, which is much higher in the biofilm than in other cell cultures."

Katja Bühler first saw biofilms when she had no idea what was hidden behind the slime: She comes from a seafaring family, her father used to sail the seas as a marine engineer. "And that thing that forms on the hull of a ship, which sailors don't like at all - that's also a biofilm!" Meanwhile, Katja Bühler did not inherit her enthusiasm for the water. "When my father used to sail, I was always very happy to be there, but not as an active sailor, more as ballast," she says with a laugh. She was in South Africa with her parents for a long time when her father changed jobs, inland and thus completely out of touch with the sea. After studying in Hamburg, she moved to Zurich as a postdoc, became a group leader for technical enzymology at the University of Dortmund, and in 2015 received her dual appointment at the UFZ in Leipzig and as a professor for the technology of productive biofilms at the TU Dresden.

"Leipzig is a great city," she says, raving about the flair in the summery old town. And once again, she has plenty of water around her; sometimes she canoes along the canals with her husband and two children in their early teens - with the best view of the UFZ high-rise building on whose roof she will soon place the first microbial reactor.

Producing hydrogen naturally - without industrial electrolysis

"So far, our systems have a volume of just under two milliliters, " she says. Gradually, she wants to increase the volume to a liter once the technology is balanced. And that's not easy: "You force the cells to do something that makes no sense to them. The cell is naturally designed to generate biomass by dividing itself. But we want it to stop growing to a large extent and direct most of the energy it obtains from the sun into hydrogen production instead. That's not really what evolution is after."

But the appeal of the process is obvious: Until now, hydrogen has been produced primarily in an industrial electrolysis process that uses green electricity to break water down into hydrogen and oxygen. The electrical energy used in the process is converted into chemical energy and stored in the hydrogen. Bioreactors, on the other hand, produce hydrogen in a direct way, without the intermediate step of energy conversion at all. But Katja Bühler knows that it will be a long time before the technology can be used on a larger scale. Her goal is to produce enough hydrogen to power a single-family home - "that could be done on a common roof surface."

Expert on the German government's National Hydrogen Council

She herself is now contributing her know-how at a political level: for a few months now, she has been a member of the National Hydrogen Council, which was set up by the German government in 2020. Twenty-six experts from science, industry and civil society sit on it. Their task is to advise the German government on how to implement the National Hydrogen Strategy. "I was already there at the first meetings and got an overview," says Katja Bühler.

In her scientific work, meanwhile, she is concerned with making hydrogen even more versatile and economical - soon also on the roof high above Leipzig. "We want to produce biologically generated hydrogen in an efficient, environmentally friendly and resource-saving way. To bring our basic research into technological application, we are working closely with partners from science and industry," explains Katja Bühler. She has no lack of a motivated team, and the view of the reactor at dizzy heights has given the team renewed impetus, she says with a laugh: "The workplace with the panoramic view up there is highly popular!"

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