Stock, F. (2019). Ghent University. Faculty of Science, Ghent, Belgium. 
[PhD thesis]. 

Quorum sensing mediated interactions between bacteria and diatoms

In plants and in the seaweed Ulva a class of bacterial signaling molecules, N-acyl homoserine lactones (AHLs), induce a range of different responses. These include growth stimulation, alteration of root morphology, induced resistance and chemokinesis. The phenomenon that prokaryotic signaling molecules trigger specific responses in eukaryotes coined the term “cross-kingdom interactions”. Recently, the micro-environments around algal cells have been proposed as places where diatoms might be exposed to a range of bacterial quorum sensing (QS) signaling molecules, such as AHLs and alkyl-quinolones. However, to date very little is known about responses of diatoms to these bacterial signaling compounds and their distribution and concentrations in diatom-dominated habitats. 

In this thesis, we identified AHLs in natural sediment samples and propose a methodological approach from sampling to AHL quantification. Furthermore, physiological studies clarified how growth inhibiting quorum sensing compounds, i.e. alkyl-quinolones and tetramic acids, interfered with diatom photosynthesis. Finally, this thesis is concluded with a transcriptome study to obtain a broader perspective on changes in gene expression induced by two AHL homologs and an AHL-derived bioactive tetramic acid rearrangement product. [Full thesis]