Impact of Invasion and Environmental Change upon the Microbiome of an Algal Holobiont

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Holobionts require the functional support of associated microorganisms and the required functions are primarily determined by missing functions of the host. At the same time certain associated microorganisms such as opportunistic pathogens may also feature functions that could be detrimental to the host. A functional holobiont therefore requires a stable equilibrium of functions. Transportation into a new and different environment could obviously disturb this equilibrium, for example if important components of the associated microbial community cannot survive.On the other hand in the new environment non-native hosts may be confronted with microbes that feature new combinations of beneficial and detrimental functions. Such challenges could drive a selection of host individuals that have a special capacity for the formation of a stable equilibrium of functions with the new microepibiont community. These important aspects of holobiont invasion biology are nearly unstudied and will be studied for the first time with a macroalgal host, Gracilaria vermiculophylla, in this project. The species is considered as one of the more problematic marine invasive macroalgae and an urgent necessity to understand the determinants of this success is apparent. Moreover, G. vermiculophylla is currently the only invasive seaweed that fulfills an important precondition for common garden experiments: an established protocol for sampling and transportation on a global scale without loss of host individuals exists. A first objective is to investigate whether (a) any bacterial taxa are consistently associated with this algal host at locations in its native range (Asia) and in its non-native range (Europe and the American East and West coasts) and whether (b) any functions are consistently overrepresented in those associations. If this is the case then the identified taxa or functions could represent a core microbiome that is necessary for long term survival and invasion success of the host. In a second step we will follow the taxonomic and functional reassembly of disturbed microbiomes on host individuals that originate from native and non-native Gracilaria populations and are exposed to identical pools of settlers in common gardens. This approach will allow it to evaluate the interactive effect of settler availability and environment upon the microbiome assembly (objective 2) and to detect any differences in host-microbiome interactions among the different algal populations (objective 3).