Pseudomonas lipopetide biosurfactants are amphiphilic molecules with a broad range of natural functions. Due to their surface active properties, it has been suggested that Pseudomonas lipopetides potentially play a role in biodegradation of hydrophobic compounds and have essential functions in biofilm formation, however, detailed studies of these roles have not yet been carried out.

The overall aim of this PhD project was therefore to elucidate in more depth the roles played by Pseudomonas lipopetides in pollutant biodegradation and biofilm formation.
This study investigated the effect of the Pseudomonas lipopeptides belonging to different structural groups on important biodegradation parameters, mainly; solubilization and emulsification of hydrophobic pollutants (alkanes and PAHs) and increase of cell surface hydrophobicity of bacterial degraders. Ultimately, it was tested if these parameters led to an increased pollutant biodegradation. It was found that lipopetides were efficient in pollutant solubilization and emulsification, and also affected degrader cell surface hydrophobicity. However, these effects had only transient or no influence on pollutant biodegradation.

The specific roles played by Pseudomonas lipopeptides in biofilm formation were elucidated for the model strain P. fluorescens SBW25, which produces the lipopeptide viscosin. Biofilm formation of this strain was compared to a viscosin deficient mutant in both static batch cultures and in hydrodynamic flow-cell systems coupled to confocal microscopy. As it was found that viscosin played a role in biofilm dispersal, the timing and localization of viscosin biosynthetic gene expression was monitored using a fluorescent bioreporter construction.

Overall the PhD project contributes with novel knowledge on potential application of Pseudomonas lipopetide biosurfactants in pollutant biodegradation and natural roles in biofilm formation. The work presented is a combination of environmental microbiology and exploiting genetic manipulation of pure cultures to achieve insightinto the effects and mechanisms of lipopeptides on microbial processes and physiology.