PhD Defense Morten Lindqvist Hansen

Supervisor
Professor MSO Lars Jelsbak, DTU Bioengineering
Co-Supervisor
Associate Professor Ling Ding, DTU Bioengineering
Examiners
Professor Ákos Kovács, DTU Bioengineering
Associate Professor Mette Nicolaisen, University of Copenhagen
Professor Jos Raaijmakers, Leiden University
Chair
Senior Researcher Eva Sonnenschein, DTU Bioengineering

Bacteria, including Pseudomonas species, exist in complex microbial communities in natural environments, such as soil, where they continuously secrete chemical molecules in the form of secondary metabolites. These metabolites are highly specialized molecules mostly known for their antimicrobial activities. However, recent research indicates that these secondary metabolites may play more diverse roles in nature in terms of microbial signaling, motility and even serve as nutrients for other microbes.

We have focused on secondary metabolites from the species Pseudomonas protegens, which is a known biocontrol bacterium. Previous studies have clearly demonstrated the link between secondary metabolism and suppression of disease caused by pathogenic microorganisms. Though, little effort has been devoted to understanding the role of these metabolites in natural environments.

During the PhD project, we developed two approaches to study the microbial ecology of Pseudomonas species. Firstly, we developed a culture-independent method to address the Pseudomonas diversity in natural environments. Secondly, we engineered a whole-cell biosensor to detect a specific secondary metabolite to aid in the screening of species isolates.

Additionally, we provide two case studies of microbial interactions and their effect on secondary metabolism in Pseudomonas. The first study describes a sequential interaction between two closely related Pseudomonas species, affecting the secondary metabolism in P. protegens. The second study addresses the contribution of Pseudomonas-produced metabolites in the ability of P. protegens to invade a microbial community.

Taken together, the PhD project has provided novel insight into the role of Pseudomonas-produced secondary metabolites in microbial interactions. It further unfolds the potential for Pseudomonas-mediated biological control and engineering of soil- and plant-associated microbiomes.