A microbiologist can't let their sourdough die

Microbes are just so cool

Ever since high school, Judith Behnsen has loved everything small. As much as she enjoyed studying biology in general, she found plants and animals much less fascinating than microbes and their superpowers. An individual bacterium doing its thing, living anywhere, from the depth of the ocean to the hottest springs to the human body—Judith knew from the beginning that she would stick with microbes. Even to this day, the versatility of microbes continues to amaze her. When there is no oxygen for bacteria to respire, Judith is fascinated by how ‘they just use other terminal electron acceptors and continue to thrive’. Her fascination with bacteria also extends to life outside of the lab. She has her own microbes at home to make quark—a German yoghurt-like specialty—and to diligently maintain her sourdough starter culture. After two years into the pandemic, she states: ‘as a microbiologist, at this point it's a sense of pride to not let the sourdough die’.

Microbial fermentation is not only important to produce human food but is also crucial for bacteria and fungi living in the human gut. In her lab, Judith is studying how commensal and pathogenic bacteria and fungi interact with each other, with the human host and how they create microbial communities (Santus et al., 2021). Additionally, she is interested in understanding how Salmonella bacteria establish infections in the human gut since Salmonella Typhimurium infection is still a leading cause of food-borne illnesses worldwide. Due to her expertise in this distinct niche, Judith is section editor for the FEMS journal microLife, overseeing the topics of gut microbiome, fungal microbiome, gnotobiotics and Salmonella pathogenesis.

Learning how gut microbes thrive

Judith's research specifically focuses on Enterobacteria that commonly live in the human gastrointestinal tract as commensals, pathobionts but also pathogens. Judith aims to unravel how microbes compete with each other and with the host for metal ions. This focus was established during her time as a postdoctoral researcher, where she revealed a previously unknown role for the host cytokine IL-22 in microbial pathogenesis (Behnsen et al., 2014). It was known that IL-22 was upregulated in bacterial infections and subsequently induced expression of antimicrobial proteins like lipocalin-2 and calprotectin. It was therefore surprising that Judith and her co-authors found IL-22 to boost the colonization of a pathogenic bacterium. Their paper elucidated the underlying mechanism, showing that Salmonella Typhimurium can use lipocalin-2 and calprotectin to sequester metals and thus overcome metal starvation. This strategy allows the pathogen to outcompete susceptible competitors like commensal E. coli in the gut.

Judith also seeks to understand how commensal and beneficial Escherichia coli acquire essential metals in the gut environment. In a recently published article, she showed that the probiotic strain E. coli Nissle 1917 uses the siderophore yersiniabactin as a metallophore to sequester zinc under physiological conditions (Behnsen et al., 2021). Judith's research thus shed light on the mechanisms that probiotic and pathogenic bacteria use to outcompete gut commensal bacteria and thrive in an inflamed gut.

To understand the distinct roles of the multitude of species in the gut microbiome, Judith's lab employs gnotobiotic mouse technology. Gnotobiotic mice are colonized by defined microbial communities that enable Judith and her team to study specific microbial interactions in the gut. For her work, she even established the first germ-free mouse facility at the Department of Microbiology and Immunology at the University of Illinois Chicago, where she is currently holding an Assistant Professor position.

Being trained and training the next generation of scientists

As she states it, she ‘did not plan for a microbiology research career in academia’. She just always followed her scientific interests towards the next career step. With a degree in Biology, she went on to study the opportunistic human pathogenic fungus Aspergillus fumigatus at the Leibniz Institute for Natural Product Research and Infection Biology in Jena, Germany and earned her PhD. She then moved to the USA for her postdoctoral research in Salmonella pathogenesis at the University of California, Irvine. She considers herself lucky to have had outstanding mentors and many positive experiences throughout her career. This inspired her to continue research in an academic setting and form her own research group. She values the fact that the position is ‘tenure-track’, allowing her to transition into a permanent professorial appointment after establishing a successful independent research program.

Leading a research group differs significantly from bench work and requires a new set of skills, but Judith enjoys the multiple facets of her new role. While she is not the one performing the majority of the experiments at the bench anymore, she is now busy outlining projects, writing grant applications and manuscripts, teaching as well as establishing research collaborations. She particularly enjoys mentoring her trainees—be that postdocs, graduate or undergraduate students—as well as the conversations about exciting new findings or the troubleshooting of yet unsuccessful experiments. Her motivation to be an inspiring mentor for her trainees can be traced back to her own mentors that accompanied her on her academic journey. Since they were and continue to be highly supportive of Judith and her career, she wants ‘to pay this forward and be the best mentor possible’. Her aim is that trainees leave the lab with an excitement for science and motivated for the next step in their career, be that in industry or academia, research or teaching.

One way to connect with her trainees is via instant communication platforms like Slack. Thanks to this, lab members can reach her anytime to update her on their newest results, like the exciting hits from a recent transposon screen. Results from this experiment will hopefully shed light on the genetic components of a new competition mechanism of Proteus mirabilis that Judith and her team described last year (Kiani et al., 2021). Serendipitously, they discovered the previously unknown ability of P. mirabilis, a commensal in the gut microbiota, to kill E. coli and other species of Enterobacteria. Judith and her team are now trying to understand which contact-dependent killing system mediates this highly efficient killing, as the obvious candidate, the Type 6 Secretion System, seems not to be involved. Sounds like this will be another interesting research paper that can be expected from Judith's group in the coming years!

Conflict of interest statement

The author was commissioned by FEMS to write this article.

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