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Published: 2021-10-04

Studying the interplay between host cell and pathogen

PROFILE Barbara Sixt wants to know how human cells can fight pathogenic bacteria, when the bacteria find their way into the cell to grow and survive there. Using this knowledge and understanding of how the bacteria manage to overcome the defence mechanisms of human cells, researchers may find novel ways to eliminate the pathogen to stop the disease.

Text: Inger Nilsson

“A human cell uses various strategies to combat intracellular bacteria,” says Barbara Sixt. “It can block the growth of the microbe or kill the pathogen, or kill itself as a defence mechanism to deprive the bacterium of its growth niche. With increased knowledge on how microbes fight back to prevent their host cells from activating their defence mechanisms, we may be able to find means to reactivate the cell’s own defence against infections as a new path of fighting infectious diseases.”

Focusing on one bacterium

Barbara Sixt’s research focuses on one bacterium in particular – Chlamydia trachomatis. This bacterium causes eye infections that can lead to blindness, but it is also a common cause of sexually transmitted diseases that can lead to infertility and complications during pregnancy. Now, researchers have found new tools to study this bacterium.

Previously, researchers haven’t been able to manipulate genes in Chlamydia

“To study the interplay between host cell and pathogen, we use molecular genetic techniques to manipulate the genes of the host cells and the pathogen. In that way, we can disarm the cells or the bacterium in the lab to study the defence mechanisms and the bacterial counterattacks. Previously, researchers haven’t been able to manipulate genes in Chlamydia. But the methods we’re using now are new – and in constant progress.”

Barbara Sixt grew up in Austria and studied at the University of Vienna. She likes animals and first considered becoming a veterinarian, but instead fell for molecular biology mechanisms and discovered how exciting it was to study the smart survival strategies of bacteria. That is why she decided on becoming a researcher instead.

During her doctoral studies in Vienna, Barbara Sixt studied bacteria that are closely related to the human-infecting pathogen Chlamydia trachomatis but which do not infect humans, but instead infect amoebae – unicellular organisms found in soil. She discovered that human cells and animal cells exposed to these bacteria have the ability to commit a ‘programmed cell death’, which means that cells that are infected with the bacteria can activate a self-destruction programme to prevent the growth and spread of the pathogen.

Collaborating with chemists

“My current work is still inspired by this original discovery. I didn’t want to change my direction since there is still so much to discover, so I’ve continued to work with what I started on all those years ago. I particularly want to understand how the human infecting Chlamydia trachomatis bacterium can prevent cells from ‘committing suicide’ as a defence mechanism.”

After a three-year postdoctoral position in the US and one and a half years in Paris, Barbara Sixt came to Umeå University in 2018 at which point she started her own lab. She is now researcher and group leader at MIMS, the Laboratory for Molecular Infection Medicine Sweden.

“To me it’s important that the group is successful, but also that the researchers in my group are able to progress in their careers. We are around six people and that’s a reasonable group size. We’re a great team! Umeå is also a great place for collaborations. For instance, we’re planning on collaborating with chemists to see if we can find new drugs that can activate host cell defences to fight infections.”

The effects of the pandemic

The pandemic has been a cause of worries for Barbara Sixt and her research group in Umeå.

“We conduct most of our work in the lab, which at the start of the pandemic meant I was worried about a potential lockdown. It’s also been difficult to recruit staff. Many people haven’t wanted to or dared to move here during the pandemic and communication has suffered. Sometimes I have felt slightly disconnected.”

But at the same time, being forced to slow down somewhat also had some advantages.

This isn’t just a job to me

“Although I haven’t had the opportunity to travel, I’ve still participated in virtual meetings and online conferences that I wouldn’t have been able to go to otherwise.”

The decision to become a researcher was a no-brainer. Many researchers spend time in the industry, but to Barbara Sixt, that was never on the table.

“This isn’t just a job to me. Working as a researcher and group leader gives me so much freedom to follow my curiosity, and I can’t imagine having a job where I couldn’t pursue that.”

Short biography

Barbara Sixt is researcher and group leader at the Department of Molecular Biology, and also affiliated to the Laboratory for Molecular Infection Medicine Sweden, MIMS, both at Umeå University.

Barbara Sixt grew up in Austria and studied molecular biology, became interested in infection biology and completed her doctoral studies in Vienna. Subsequently, she held a three-year postdoctoral position at Duke University in the US followed by a year and a half in Paris. She came to Umeå University in 2018.


Short facts

Name: Barbara Susanne Sixt

Family: My cat has accompanied me from the US to France and then to Sweden. The rest of my family is in Austria.

Comes from: I was born and raised in Vienna, Austria.

Lives: At Tomtebo in Umeå, near the Nydala Lake.

Motivates me at work: I’m driven by curiosity. Biology is fascinating and there is still much to discover.

Inspires me: What inspires me the most are the microbes themselves. They are so smart.

Best way to relax: I like spending time outdoors, in nature, and to take long walks. I also like reading fantasy novels, which is a strong contrast to science.