Goecke, Franz Ronald (2011) Associations between microbes and macroalgae: Host, epiphyte and environmental factors. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, 149 pp.

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Abstract

During the last 3 years, there was a special enhancement of research focused on association between macroalgae and bacteria. The present work was carried out in order to contribute towards our understanding of those alga-bacteria relationships. Different macroalgae in the same habitat may all exert the same important ecological role as primary producers, but in terms of interactions every single species represents a completely different microenvironment occupied by rich and diverse microbial communities. The present study covered potential effects from the host, season and epibiota in regulating the associated microbial communities. It also covered pathogenic relationships and possible specific associations.
Recently it has been demonstrated by molecular methods that different species of marine macroalgae in the same habitat are associated with different microbial communities. We
confirmed these molecular data by means of a cultivation-based study on two co-occurring macroalgae from the Baltic Sea. Those very unique microenvironments may be formed by the thallus morphology, by microtopography of the surface and by unique metabolic properties (e.g. secondary metabolites and cell wall structures). All these factors were shown to influence the associations with organisms of their immediate surroundings. The present study also confirms algae as a distinct source of bacteria by a phylogenetic study of all newly described bacteria from algal sources available in GenBank.
The association of algae with members of the microbial community may represent an ecological advantage against microbial epibiosis. The development of antimicrobial
metabolites is widespread among alga-associated bacteria, a quality which the macroalgae may use for it´s own benefit. A mutualistic relationship can be postulated, in which the
bacterial community protects the host from biofouling, while the host may provide nutrients and physical protection to the bacteria. The role of the associated bacteria as defense of the host against pathogens is almost completely unknown, starting with the fact that diseases of
algae are mostly neglegted. In this sense, we described a microbial pathogen affecting a macroalga at the Chilean coast. Algae are key components of the aquatic environments, not only habitats for many macroorganisms, but also for millions of microbes waiting to be discovered. Because chemical compounds seem to rule the macroalga-bacteria relationships, host and epibiota represent also a potential rich source of secondary metabolites. Both, macroalgae and microbes are key organisms in marine environments. Nevertheless, we are only starting to
discover the complexity of relationships between algae and bacteria in nature.

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