Effects of climate variability on interactions between cyanobacteria and associated microheterotrophs-consequences for development of toxic cyanobacterial blooms

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Recent studies on seasonal dynamics of phytoplankton in fresh and brackish lakes, in particularly on acyclic cyanobacterial blooms in lakes of Northern Germany, suggest multiple interactions rather than individual mechanisms being responsible for the development of cyanobacterial blooms. Variability of temperature is one key factor leading to marked changes in interactions between cyanobacteria and heterotrophic bacteria in terms of symbiosis, parasitism, commensalisms etc. These changes affect the seasonal dominance pattern and may also lead to a decoupling of previously synchronised food webs. By using pure cultures of common and potentially toxic cyanobacteria (Nodularia spumigena, Anabaena spp., Microcystis aentginosa (flos-aquae) incubated with natural and defined communities of heterotrophic bacteria the proposed project aims to experimentally test the following hypotheses: a) Rising temperatures cause severe changes in interactions between cyanobacteria and heterotrophic bacteria, b) Due to a tight coupling between cyanobacteria and heterotrophic bacteria changes in the community composition of heterotrophic bacteria will impact the development of cyanobacteria and may cause decoupling of presently synchronised food webs (mismatch). Underlying mechanisms concerning the role of specific heterotrophic bacterial communities will be investigated using molecular (phylogeny) as well as classical microbiological (physiology) methods.