ABSTRACT
Brown macroalgae are colonized by diverse microorganisms influencing the physiology of their host. However, cell-cell interactions within the surface microbiome (epimicrobiome) are largely unexplored, despite the significance of specific chemical mediators in maintaining host-microbiome homeostasis. In this study, by combining liquid chromatography coupled to mass spectrometry (LC-MS) analysis and bioassays, we demonstrated that the widely diverse fungal epimicrobiota of the brown alga Saccharina latissima can affect quorum sensing (QS), a type of cell-cell interaction, as well as bacterial biofilm formation. We also showed the ability of the bacterial epimicrobiota to form and inhibit biofilm growth, as well as to activate or inhibit QS pathways. Overall, we demonstrate that QS and anti-QS compounds produced by the epimicrobiota are key metabolites in these brown algal epimicrobiota communities and highlight the importance of exploring this epimicrobiome for the discovery of new bioactive compounds, including potentially anti-QS molecules with antifouling properties.
ABSTRACT
Genomic islands (Aeromonas salmonicida genomic islands, AsaGEIs) are found worldwide in many isolates of Aeromonas salmonicida subsp. salmonicida, a fish pathogen. To date, five variants of AsaGEI (1a, 1b, 2a, 2b and 2c) have been described. Here, we investigate a sixth AsaGEI, which was identified in France between 2016 and 2019 in 20 A. salmonicida subsp. salmonicida isolates recovered from sick salmon all at the same location. This new AsaGEI shares the same insertion site in the chromosome as the other AsaGEI2s as they all have a homologous integrase gene. This new AsaGEI was thus named AsaGEI2d, and has five unique genes compared to the other AsaGEIs. The isolates carrying AsaGEI2d also bear the plasmid pAsa7, which was initially found in an isolate from Switzerland. This plasmid provides resistance to chloramphenicol thanks to a cat gene. This study reveals more about the diversity of the AsaGEIs.