PhD Defence by Emmelie Joe Freudenberg Rasmussen

Principal supervisor:

• Professor Peter Ruhdal Jensen

Co-supervisors:

• Associate Professor Christian Solem
• Personal Professor Michiel Kleerebezem
• Senior Scientist Jos Boekhorst

Examiners:

• Associate Professor Anurag Kumar Singha, DTU Food
• Associate Professor Hermie J. M. Harmsen, University Medical Center Groningen
• Senior Research Fellow Kim Ib Sørensen, Novonesis

Moderator at defence:

• Associate Professor Timothy John Hobley

Resume
The human gut is home for trillions of bacteria, of which many play an essential role in digestion, immunity, and overall health. For these bacteria to thrive, they need access to vital nutrients, including vitamins. However, relatively little is still known about how gut bacteria obtain and share these nutrients with one another and how important it might be. The work explores the role of vitamin B2 (riboflavin) and investigates how bacteria use this vitamin to survive and maintain a healthy intestinal environment.

The research focused on the genus Faecalibacterium, which is one of the most important beneficial bacteria in the human gut. Faecalibacterium are associated with anti-inflammatory properties and is often reduced in individuals with intestinal inflammation. Riboflavin might have an important protective role in this context. The study revealed that some Faecalibacterium strains can produce riboflavin themselves, while others must obtain it from their surroundings, investigating how access to this vitamin influences their survival in the gut.

To identify possible sources of riboflavin, lactic acid bacteria commonly used in food fermentations was investigated. A particular strain of Lactococcus lactis was found to produce and release large amounts of riboflavin. Furthermore, it was demonstrated that this bacterium could supply riboflavin to Faecalibacterium, providing evidence that different gut microbes can support one another through vitamin sharing.

The thesis also examined how antioxidants influence the gut microbiome, especially after disruption by antibiotics. These studies improve our understanding of how gut bacteria respond and recover from environmental challenges.

A key finding in this work is that microbial exchange of riboflavin can help beneficial gut bacteria survive under physiologically relevant conditions. The findings advance our understanding of interactions within the gut microbiome and may support the development of new microbiome-based strategies for improving intestinal health. Beyond healthcare applications, the riboflavin-producing bacterium was successfully used to naturally enrich plant-based foods, including soy and oat products with vitamin B2.

A copy of the PhD thesis is available for reading at the department.