PhD Defense Nathalie Nina Suhr Eiris Henriksen

Microbial secondary metabolites have been exploited by humankind for decades, especially as antibiotics. Naturally, it has been the perception that the antibiotic properties also define
their predominant role in nature - as weapons to kill competitors. However, within microbial communities, these complex molecules can play a broad range of roles ranging from facilitators of cooperation to exploitative competition. Evidently, through their ability to modulate the behaviour of microorganisms, secondary metabolites may in part be responsible for shaping microbial communities. However, natural microbial communities are complex, thus deciphering the role(s) of secondary metabolites within these dynamic assemblages can be challenging, which have led most studies to examine the metabolites and its producer under contrieved condition, thus the true ecological roles of microbial secondary metabolites are not elucidated.

In this project, we developed and used marine microbial model systems to investigate the presence and influence of microbial secondary metabolites in marine microbial communities. Using an in situ model system we followed the development of a marine microbial biofilm community in coastal seawaters, which allowed for novel insight into the temporal dynamics of secondary metabolites during natural microbial community development. Furthermore, using a marine algal model system, we explored how the marine bacteria Phaeobacter inhibens, that produces the multifunctional compound tropodithietic acid, influences other bacterial strains over time. This study showed that closely related strains are the most affected in the microalgae community. Lastly, we commenced exploring
a future model eukaryotic host system, the bryozoan Conopeum seurati, that will allow for investigations of the spatial distribution and ecological role of TDA-producing bacteria in
nature. This project concludes that developing microbial model systems, based on ecological principles, can aid in examining the influences of secondary metabolites on microbial communities and be used to evaluate the true ecological role(s) of microbial secondary metabolites in nature.