title: Seasonal and spatial patterns of microbial diversity along a trophic gradient in the interconnected lakes of the Osterseen Lake District, Bavaria.
abstract: The Osterseen Lake District in Bavaria consists of 19 small interconnected lakes that exhibit a pronounced trophic gradient from eutrophic to oligotrophic. It therefore presents a unique model system to address ecological questions regarding niche adaptation and Baas Becking's long standing hypothesis of "everything is everywhere, but the environment selects." Here, we present the first assessment of the microbial diversity in these lakes. We sampled the lakes in August and December and used 454 pyrosequencing of 16S rRNA amplicons to analyze the microbial diversity. The diversity patterns between lakes and seasons were compared and the bacterial community composition was correlated with key chemical and physical parameters. Distinct patterns of bacterial diversity only emerged at the level of individual OTUs (operational taxonomic units), but not at the level of the major bacterial phyla. This emphasizes the high functional and physiological diversity among bacterial species within a phylum and calls for analysis of biodiversity at the level of OTUs in order to understand fine-scale biogeography. We were able to identify a number of cosmopolitan OTUs as well as specialist OTUs that were restricted to certain lakes or seasons, suggesting adaptation to specific ecological niches.
authors.affiliation: Aquatic Systems Biology Unit, Limnological Research Station Iffeldorf, Department of Ecology and Ecosystem Management, Technical University of Munich Munich, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Zwirglmaier
authors.affiliation: Aquatic Systems Biology Unit, Limnological Research Station Iffeldorf, Department of Ecology and Ecosystem Management, Technical University of Munich Munich, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Keiz
authors.affiliation: Helmholtz Zentrum München, Scientific Computing Research Unit, German Research Center for Environmental Health Neuherberg, Germany.
authors.forename: Marion
authors.initials: M
authors.lastname: Engel
authors.affiliation: Aquatic Systems Biology Unit, Limnological Research Station Iffeldorf, Department of Ecology and Ecosystem Management, Technical University of Munich Munich, Germany.
authors.forename: Juergen
authors.initials: J
authors.lastname: Geist
authors.affiliation: Aquatic Systems Biology Unit, Limnological Research Station Iffeldorf, Department of Ecology and Ecosystem Management, Technical University of Munich Munich, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Raeder
keywords: 454 amplicon sequencing; Osterseen Lake District; bacterial diversity; freshwater lakes; microbial ecology; niche adaptation; trophic gradient