User:Frank Persson

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Chemical defence of red algae against bacteria

Just like any aquatic surface, marine benthic macroalgae (seaweeds) are subjected to biofilm formation. This is often disadvantageous for the algae. Epiphytic bacteria can indirectly cause negative effects by providing positive settlement cues for macroscopic fouling organisms and pathogenic bacteria can cause severe tissue damage, even mortality. Despite that seaweeds are constantly exposed to potentially pathogenic bacteria, they often seem to remain free of diseases. Since seaweeds lack an immune system, they must either tolerate microbial attacks, or be defended by other means. It has often been hypothesized that seaweeds are chemically defended against bacteria and several studies have shown that seaweeds produce antibacterial compounds. Most studies have however focused on finding substances for pharmacological and antifouling applications. Consequently, the ecological roles of algal antibacterial compounds are most often unknown. In this project, which is performed in cooperation with Marine Ecology at Tjärnö as part of the research program MARICE (Göteborg University), chemical defence/interactions between red algae within the family Bonnemaisoniaceae and their epiphytic bacteria is investigated. Several members of this algal family produce halogenated secondary metabolites with potential antifouling properties and some species are common members of the benthic flora in Skagerrak. Previous to this project it was shown that one species, Bonnemaisonia hamifera, have comparably few epiphytic bacteria and that substances extracted from the surface of the algae could inhibit bacterial growth. Since then, we have identified the major antibacterial compound of B. hamifera and determined natural concentrations at the surface of the alga. These natural surface concentrations did inhibit bacterial colonisation of coated field panels as well as growth of algal derived isolates of bacteria, with indications of a phylogenetic inhibitory specificity. Tentative results have also indicated that B. hamifera could coat nearby surfaces with the compound at significant concentrations, thereby expanding the spatial ecological role. Furthermore the related algal species Bonnemaisonia asparagoides was found to also possess (so far unidentified) substances at their surface that inhibit bacterial growth at natural surface concentrations.

Presently we try to investigate to what extent the antifouling compounds affect the epiphytic bacteria with regard to activity and community structure (T-RFLP, clone libraries); if the compounds really protect the algae against any bacterial threats or other negative interactions; and what the costs are for maintaining the potential chemical defences. The set up include comparative field studies of algae and artificially coated panels as well as manipulative studies at the lab where the B. hamifera production of the major antifouling compound is regulated.

The project is part of the interdiciplinary research program MARICE [1]

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