Blue gloves, white coat, the smell of disinfectant in the air. This is Katja Krannich's working environment. She takes a cell culture vessel out of the incubator: LLC PK1. "My favorite cell line," she explains with a smile. "They are so beautifully colorful. You can see the cell division very clearly, as they already express two dyes. However, they have to be handled carefully. They are very sensitive, they don't like to separate, and yet they are stable," she explains.

Krannich is a medical-technical laboratory assistant and works as a laboratory technician at ZEISS. Every day, she prepares samples for work under the microscope. She works with different cell lines, all of which require different handling. The work is varied, and a lot comes down to experience and the courage to try things out. "If the cells don't grow or look like you want, it's a matter of developing a feeling for what to do, reacting ad hoc, deciding." Krannich is completely in her element.

In the past, when cells were needed, they had to be procured at a nearby research institute. This was sometimes complicated and time consuming. This gave birth to the idea of a cell culture lab with its own lab technician at ZEISS.

Krannich has overseen the lab since 2021 and is the "control center," as she says. She is the one who pulls all the strings. She manages equipment, devices, and hazardous materials and, of course, looks after the cells. But more importantly, she’s got her colleagues' backs so that they can focus on their core topics. She prepares samples for development, customer training, application development, product management, and occasionally for central research.

To grow the cell culture and keep it alive, the cells should be moved regularly. Krannich routinely performs the so-called passaging or splitting of cells on Monday, Thursday, and Friday, or as needed. In the meantime, she monitors the general condition of the cells and the growth of the culture with a microscope. It is important to prevent contamination or detect it early. Sterile work is essential.

An important indicator for the time of splitting is the so-called confluence. This refers to the largely gapless coverage of the bottom surface of a culture vessel with cells. Very close cell-to-cell contact affects their behavior, and most cells then stop dividing, so they have to be sub-cultured promptly if they are to survive.

"Our cell lines are roughly similar, but some either need a special medium or other additives, are easier or harder to detach from the culture vessel, or grow better on coated vessels. The timing for splitting varies, and some 'cell clusters' are difficult to separate," Krannich says. A lot depends on her intuition and sensitivity. She draws on her extensive experience with the different cell lines, gained over more than 15 years at a national institute for virology.

Krannich's special tasks include preparing samples for live cell imaging, cell arrest, plasmid transfection, immunofluorescence, and the production of permanent preparations. These processes sometimes run for an entire week and must be precisely monitored. "I have to keep to exact times; a lot of subtleties matter," she notes.

The staining of different cell components challenges her again and again: be it live cell staining, transfection, or immunofluorescence. "Once I had an important client workshop coming up. The clock was ticking and the cells didn't look like they should," she reports excitedly. "But fortunately, I quickly came up with a plan B and was then able to provide 'fancy' cells after all."