Isolated thallus-associated compounds from the macroalga Fucus vesiculosus mediate bacterial surface colonization in the field similar to that on the natural alga

This study investigated whether surface-associated compounds isolated from the macroalga Fucus vesiculosus had the potential to mediate microbial and/or macrobial epibiosis similar to that on the natural alga. To selectively yield thallus-associated compounds and avoid contamination by intracellular algal compounds, cell lysis was monitored by surface microscopy of algal cells and chemical profiling of algal surface extracts by coupled gas chromatography mass spectroscopy. The optimized extraction resulted in polar and non-polar algal surface extracts. The non-polar surface extract was immobilized in hydrogel, the polar surface extract was homogeneously perfused through the gel to ensure a temporally constant delivery of polar extract components. During a 7 day field trial, bacterial biofilms were formed on control gels and gels featuring polar and/or non-polar extract components. PERMANOVA revealed that bacterial community profiles on controls and on gels featuring polar or non-polar extract were significantly different from the profile on F. vesiculosus, while the profile on the gels bearing both polar and non-polar extracts was not. Moreover, the polar surface extracts inhibited the settlement of barnacle cyprids. Considering the pronounced effects of bacterial biofilms on invertebrate larval settlement, these results suggest that algal surface chemistry affects macrofouling not only directly but also indirectly, via its control of biofilm formation and composition.