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It’s all about the cell wall for brand-new professor Dennis Claessen

Dennis Claessen has been appointed professor of Molecular Microbiology at the Institute of Biology Leiden. With his teaching and research on the cell wall, the professor wants to establish applications in the industry and the medical sector.

‘Scientifically speaking, 2020 is not even such a bad year for me’, Dennis Claessen says, smiling, at the start of the video-interview. An understatement, because this year he received a prestigious VICI grant from the Dutch Research Council, his students were awarded in international competitions, and on 11 November he received the news of his appointment as professor of Molecular Microbiology. The first thing he did? ‘I promised my kids to bake pancakes and walk St. Maarten with them, so we did.’

Bacteria without a coat

Microbiologist Dennis Claessen has devoted his entire career to the cell wall of bacteria. It starts at the University of Groningen, where Claessen specializes in molecular biology and microbiology. During an internship, he met Groningen professor Lubbert Dijkhuizen and professor Han Wösten, now working in Utrecht, from whom he will later obtain his doctorate. In his PhD research, Claessen is introduced to actinomycetes and studies the cell wall of these antibiotic-producing soil bacteria. He continues as a postdoc at Oxford and learns about research into bacteria that live without a cell wall. This seems paradoxical because the cell wall is a protective coat for a bacterium. Claessen decides that once back in the Netherlands, he wants to study this further.

Designing a new cell wall

In 2010 Claessen is hired at the Institute of Biology Leiden. He continues his research on the cell wall of antibiotic-producing bacteria. A year later, professor Gilles van Wezel joins the IBL, and the two will work closely together. A successful collaboration, and not only in the field of research; in 2011 they win the Academic Year Prize with their project Antibiotics Wanted!. With a practical lesson kit developed by them, secondary school pupils learn about antibiotic-producing bacteria and the problem of antibiotics resistance.

'It sounds like science fiction, but in ten years time, we can make big steps in it'

It is now 2020. In the role of professor and with a VICI grant in his pocket, Claessen wants to use his research on morphology and cell wall-deficient bacteria for innovative applications in the industry and the medical sector. He wants to find out, for example, whether the cell wall can be changed with the help of synthetic biology. Claessen envisions a cell wall-deficient bacterium that will receive a newly designed cell wall and thus a different shape. This way the bacterium can be used more efficiently and in a more controllable manner for the production of antibiotics and enzymes, for example. ‘It still sounds like science fiction now, but in ten years time, we can make big steps in it,’ he says.

His study into cell wall deficient bacteria is also interesting for medical applications. Claessen suspects that some pathogenic bacteria can also get rid of their cell wall. It makes them insensitive to drugs and invisible to the immune system. Claessen is investigating whether this is the case with tuberculosis bacteria because they can hide in the body for a long time.

Love for synthetic biology and education

Claessen's interest in synthetic biology reflects in his teaching. In 2010 he is introduced to iGEM, an international student competition in synthetic biology, and he is sold at once. In 2016, Claessen supervises the first fully Leiden iGEM team together with current Education director at IBL Han de Winde. The lessons they and the involved team members learn lead to better performance every year. 2020 is the highlight: the Leiden team, which has designed a test kit to detect infectious diseases, wins the main prize and five other prizes in the competition. ‘All credits go to the direct supervisors and of course the team itself’, says Claessen, who is involved as an adviser. ‘It is a great inspiration and fantastic to see the members develop in their role.’ Members of a previous iGEM team are also in the win. They come second in the international BISC-E competition with their sustainable alternative to plastic microparticles in, for example, cosmetics.

To Claessen, education is in his own words ‘great to be allowed to do’. Since recently, he is also active as chairman of the Programme Committee Biology. He sees it as a stepping stone to critically review the Leiden Biology curriculum and to be able to give concrete advice. He also likes to keep busy with the education itself: ‘I wouldn't want to lose all my teaching duties, I like to keep doing the things I enjoy.’

Header image: cell wall-deficient bacteria, coloured by fluorescent proteins. Photo: Shraddha Shitut (IBL).

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